Re: [PR] Remove patching for doc blocks. [lucene]

["gf2121 (via GitHub)" <gi...@apache.org>]

gf2121 commented on code in PR #12741:
URL: https://github.com/apache/lucene/pull/12741#discussion_r1378509674


##########
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99PostingsFormat.java:
##########
@@ -0,0 +1,518 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene99;
+
+import java.io.IOException;
+import org.apache.lucene.codecs.BlockTermState;
+import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.codecs.FieldsConsumer;
+import org.apache.lucene.codecs.FieldsProducer;
+import org.apache.lucene.codecs.MultiLevelSkipListWriter;
+import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.codecs.PostingsReaderBase;
+import org.apache.lucene.codecs.PostingsWriterBase;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsReader;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsWriter;
+import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.SegmentReadState;
+import org.apache.lucene.index.SegmentWriteState;
+import org.apache.lucene.index.TermState;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.IOUtils;
+import org.apache.lucene.util.packed.PackedInts;
+
+/**
+ * Lucene 5.0 postings format, which encodes postings in packed integer blocks for fast decode.

Review Comment:
   ```suggestion
    * Lucene 9.9 postings format, which encodes postings in packed integer blocks for fast decode.
   ```



##########
lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene90/Lucene90PostingsFormat.java:
##########
@@ -38,6 +37,8 @@
 /**
  * Lucene 5.0 postings format, which encodes postings in packed integer blocks for fast decode.

Review Comment:
   ```suggestion
    * Lucene 9.0 postings format, which encodes postings in packed integer blocks for fast decode.
   ```



##########
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99SkipReader.java:
##########
@@ -0,0 +1,206 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene99;
+
+import java.io.IOException;
+import java.util.Arrays;
+import org.apache.lucene.codecs.MultiLevelSkipListReader;
+import org.apache.lucene.store.IndexInput;
+
+/**
+ * Implements the skip list reader for block postings format that stores positions and payloads.
+ *
+ * <p>Although this skipper uses MultiLevelSkipListReader as an interface, its definition of skip
+ * position will be a little different.
+ *
+ * <p>For example, when skipInterval = blockSize = 3, df = 2*skipInterval = 6,
+ *
+ * <pre>
+ * 0 1 2 3 4 5
+ * d d d d d d    (posting list)
+ *     ^     ^    (skip point in MultiLeveSkipWriter)
+ *       ^        (skip point in Lucene90SkipWriter)
+ * </pre>
+ *
+ * <p>In this case, MultiLevelSkipListReader will use the last document as a skip point, while
+ * Lucene90SkipReader should assume no skip point will comes.
+ *
+ * <p>If we use the interface directly in Lucene90SkipReader, it may silly try to read another skip
+ * data after the only skip point is loaded.
+ *
+ * <p>To illustrate this, we can call skipTo(d[5]), since skip point d[3] has smaller docId, and
+ * numSkipped+blockSize== df, the MultiLevelSkipListReader will assume the skip list isn't exhausted
+ * yet, and try to load a non-existed skip point
+ *
+ * <p>Therefore, we'll trim df before passing it to the interface. see trim(int)
+ */
+public class Lucene99SkipReader extends MultiLevelSkipListReader {
+  private long[] docPointer;
+  private long[] posPointer;
+  private long[] payPointer;
+  private int[] posBufferUpto;
+  private int[] payloadByteUpto;
+
+  private long lastPosPointer;
+  private long lastPayPointer;
+  private int lastPayloadByteUpto;
+  private long lastDocPointer;
+  private int lastPosBufferUpto;
+
+  public Lucene99SkipReader(
+      IndexInput skipStream,
+      int maxSkipLevels,
+      boolean hasPos,
+      boolean hasOffsets,
+      boolean hasPayloads) {
+    super(skipStream, maxSkipLevels, ForUtil.BLOCK_SIZE, 8);
+    docPointer = new long[maxSkipLevels];
+    if (hasPos) {
+      posPointer = new long[maxSkipLevels];
+      posBufferUpto = new int[maxSkipLevels];
+      if (hasPayloads) {
+        payloadByteUpto = new int[maxSkipLevels];
+      } else {
+        payloadByteUpto = null;
+      }
+      if (hasOffsets || hasPayloads) {
+        payPointer = new long[maxSkipLevels];
+      } else {
+        payPointer = null;
+      }
+    } else {
+      posPointer = null;
+    }
+  }
+
+  /**
+   * Trim original docFreq to tell skipReader read proper number of skip points.
+   *
+   * <p>Since our definition in Lucene90Skip* is a little different from MultiLevelSkip* This

Review Comment:
   ```suggestion
      * <p>Since our definition in Lucene99Skip* is a little different from MultiLevelSkip* This
   ```



##########
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99SkipReader.java:
##########
@@ -0,0 +1,206 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene99;
+
+import java.io.IOException;
+import java.util.Arrays;
+import org.apache.lucene.codecs.MultiLevelSkipListReader;
+import org.apache.lucene.store.IndexInput;
+
+/**
+ * Implements the skip list reader for block postings format that stores positions and payloads.
+ *
+ * <p>Although this skipper uses MultiLevelSkipListReader as an interface, its definition of skip
+ * position will be a little different.
+ *
+ * <p>For example, when skipInterval = blockSize = 3, df = 2*skipInterval = 6,
+ *
+ * <pre>
+ * 0 1 2 3 4 5
+ * d d d d d d    (posting list)
+ *     ^     ^    (skip point in MultiLeveSkipWriter)
+ *       ^        (skip point in Lucene90SkipWriter)
+ * </pre>
+ *
+ * <p>In this case, MultiLevelSkipListReader will use the last document as a skip point, while
+ * Lucene90SkipReader should assume no skip point will comes.
+ *
+ * <p>If we use the interface directly in Lucene90SkipReader, it may silly try to read another skip

Review Comment:
   ```suggestion
    * <p>If we use the interface directly in Lucene99SkipReader, it may silly try to read another skip
   ```



##########
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99SkipReader.java:
##########
@@ -0,0 +1,206 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene99;
+
+import java.io.IOException;
+import java.util.Arrays;
+import org.apache.lucene.codecs.MultiLevelSkipListReader;
+import org.apache.lucene.store.IndexInput;
+
+/**
+ * Implements the skip list reader for block postings format that stores positions and payloads.
+ *
+ * <p>Although this skipper uses MultiLevelSkipListReader as an interface, its definition of skip
+ * position will be a little different.
+ *
+ * <p>For example, when skipInterval = blockSize = 3, df = 2*skipInterval = 6,
+ *
+ * <pre>
+ * 0 1 2 3 4 5
+ * d d d d d d    (posting list)
+ *     ^     ^    (skip point in MultiLeveSkipWriter)
+ *       ^        (skip point in Lucene90SkipWriter)

Review Comment:
   ```suggestion
    *       ^        (skip point in Lucene99SkipWriter)
   ```



##########
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99SkipReader.java:
##########
@@ -0,0 +1,206 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene99;
+
+import java.io.IOException;
+import java.util.Arrays;
+import org.apache.lucene.codecs.MultiLevelSkipListReader;
+import org.apache.lucene.store.IndexInput;
+
+/**
+ * Implements the skip list reader for block postings format that stores positions and payloads.
+ *
+ * <p>Although this skipper uses MultiLevelSkipListReader as an interface, its definition of skip
+ * position will be a little different.
+ *
+ * <p>For example, when skipInterval = blockSize = 3, df = 2*skipInterval = 6,
+ *
+ * <pre>
+ * 0 1 2 3 4 5
+ * d d d d d d    (posting list)
+ *     ^     ^    (skip point in MultiLeveSkipWriter)
+ *       ^        (skip point in Lucene90SkipWriter)
+ * </pre>
+ *
+ * <p>In this case, MultiLevelSkipListReader will use the last document as a skip point, while
+ * Lucene90SkipReader should assume no skip point will comes.

Review Comment:
   ```suggestion
    * Lucene99SkipReader should assume no skip point will comes.
   ```



##########
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99PostingsFormat.java:
##########
@@ -0,0 +1,518 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene99;
+
+import java.io.IOException;
+import org.apache.lucene.codecs.BlockTermState;
+import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.codecs.FieldsConsumer;
+import org.apache.lucene.codecs.FieldsProducer;
+import org.apache.lucene.codecs.MultiLevelSkipListWriter;
+import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.codecs.PostingsReaderBase;
+import org.apache.lucene.codecs.PostingsWriterBase;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsReader;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsWriter;
+import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.SegmentReadState;
+import org.apache.lucene.index.SegmentWriteState;
+import org.apache.lucene.index.TermState;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.IOUtils;
+import org.apache.lucene.util.packed.PackedInts;
+
+/**
+ * Lucene 5.0 postings format, which encodes postings in packed integer blocks for fast decode.
+ *
+ * <p>Basic idea:
+ *
+ * <ul>
+ *   <li><b>Packed Blocks and VInt Blocks</b>:
+ *       <p>In packed blocks, integers are encoded with the same bit width ({@link PackedInts packed
+ *       format}): the block size (i.e. number of integers inside block) is fixed (currently 128).
+ *       Additionally blocks that are all the same value are encoded in an optimized way.
+ *       <p>In VInt blocks, integers are encoded as {@link DataOutput#writeVInt VInt}: the block
+ *       size is variable.
+ *   <li><b>Block structure</b>:
+ *       <p>When the postings are long enough, Lucene99PostingsFormat will try to encode most
+ *       integer data as a packed block.
+ *       <p>Take a term with 259 documents as an example, the first 256 document ids are encoded as
+ *       two packed blocks, while the remaining 3 are encoded as one VInt block.
+ *       <p>Different kinds of data are always encoded separately into different packed blocks, but
+ *       may possibly be interleaved into the same VInt block.
+ *       <p>This strategy is applied to pairs: &lt;document number, frequency&gt;, &lt;position,
+ *       payload length&gt;, &lt;position, offset start, offset length&gt;, and &lt;position,
+ *       payload length, offsetstart, offset length&gt;.
+ *   <li><b>Skipdata settings</b>:
+ *       <p>The structure of skip table is quite similar to previous version of Lucene. Skip
+ *       interval is the same as block size, and each skip entry points to the beginning of each
+ *       block. However, for the first block, skip data is omitted.
+ *   <li><b>Positions, Payloads, and Offsets</b>:
+ *       <p>A position is an integer indicating where the term occurs within one document. A payload
+ *       is a blob of metadata associated with current position. An offset is a pair of integers
+ *       indicating the tokenized start/end offsets for given term in current position: it is
+ *       essentially a specialized payload.
+ *       <p>When payloads and offsets are not omitted, numPositions==numPayloads==numOffsets
+ *       (assuming a null payload contributes one count). As mentioned in block structure, it is
+ *       possible to encode these three either combined or separately.
+ *       <p>In all cases, payloads and offsets are stored together. When encoded as a packed block,
+ *       position data is separated out as .pos, while payloads and offsets are encoded in .pay
+ *       (payload metadata will also be stored directly in .pay). When encoded as VInt blocks, all
+ *       these three are stored interleaved into the .pos (so is payload metadata).
+ *       <p>With this strategy, the majority of payload and offset data will be outside .pos file.
+ *       So for queries that require only position data, running on a full index with payloads and
+ *       offsets, this reduces disk pre-fetches.
+ * </ul>
+ *
+ * <p>Files and detailed format:
+ *
+ * <ul>
+ *   <li><code>.tim</code>: <a href="#Termdictionary">Term Dictionary</a>
+ *   <li><code>.tip</code>: <a href="#Termindex">Term Index</a>
+ *   <li><code>.doc</code>: <a href="#Frequencies">Frequencies and Skip Data</a>
+ *   <li><code>.pos</code>: <a href="#Positions">Positions</a>
+ *   <li><code>.pay</code>: <a href="#Payloads">Payloads and Offsets</a>
+ * </ul>
+ *
+ * <a id="Termdictionary"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Dictionary</b>
+ *       <p>The .tim file contains the list of terms in each field along with per-term statistics
+ *       (such as docfreq) and pointers to the frequencies, positions, payload and skip data in the
+ *       .doc, .pos, and .pay files. See {@link Lucene90BlockTreeTermsWriter} for more details on
+ *       the format.
+ *       <p>NOTE: The term dictionary can plug into different postings implementations: the postings
+ *       writer/reader are actually responsible for encoding and decoding the PostingsHeader and
+ *       TermMetadata sections described here:
+ *       <ul>
+ *         <li>PostingsHeader --&gt; Header, PackedBlockSize
+ *         <li>TermMetadata --&gt; (DocFPDelta|SingletonDocID), PosFPDelta?, PosVIntBlockFPDelta?,
+ *             PayFPDelta?, SkipFPDelta?
+ *         <li>Header, --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>PackedBlockSize, SingletonDocID --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>DocFPDelta, PosFPDelta, PayFPDelta, PosVIntBlockFPDelta, SkipFPDelta --&gt; {@link
+ *             DataOutput#writeVLong VLong}
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>Header is a {@link CodecUtil#writeIndexHeader IndexHeader} storing the version
+ *             information for the postings.
+ *         <li>PackedBlockSize is the fixed block size for packed blocks. In packed block, bit width
+ *             is determined by the largest integer. Smaller block size result in smaller variance
+ *             among width of integers hence smaller indexes. Larger block size result in more
+ *             efficient bulk i/o hence better acceleration. This value should always be a multiple
+ *             of 64, currently fixed as 128 as a tradeoff. It is also the skip interval used to
+ *             accelerate {@link org.apache.lucene.index.PostingsEnum#advance(int)}.
+ *         <li>DocFPDelta determines the position of this term's TermFreqs within the .doc file. In
+ *             particular, it is the difference of file offset between this term's data and previous
+ *             term's data (or zero, for the first term in the block).On disk it is stored as the
+ *             difference from previous value in sequence.
+ *         <li>PosFPDelta determines the position of this term's TermPositions within the .pos file.
+ *             While PayFPDelta determines the position of this term's &lt;TermPayloads,
+ *             TermOffsets?&gt; within the .pay file. Similar to DocFPDelta, it is the difference
+ *             between two file positions (or neglected, for fields that omit payloads and offsets).
+ *         <li>PosVIntBlockFPDelta determines the position of this term's last TermPosition in last
+ *             pos packed block within the .pos file. It is synonym for PayVIntBlockFPDelta or
+ *             OffsetVIntBlockFPDelta. This is actually used to indicate whether it is necessary to
+ *             load following payloads and offsets from .pos instead of .pay. Every time a new block
+ *             of positions are to be loaded, the PostingsReader will use this value to check
+ *             whether current block is packed format or VInt. When packed format, payloads and
+ *             offsets are fetched from .pay, otherwise from .pos. (this value is neglected when
+ *             total number of positions i.e. totalTermFreq is less or equal to PackedBlockSize).
+ *         <li>SkipFPDelta determines the position of this term's SkipData within the .doc file. In
+ *             particular, it is the length of the TermFreq data. SkipDelta is only stored if
+ *             DocFreq is not smaller than SkipMinimum (i.e. 128 in Lucene99PostingsFormat).
+ *         <li>SingletonDocID is an optimization when a term only appears in one document. In this
+ *             case, instead of writing a file pointer to the .doc file (DocFPDelta), and then a
+ *             VIntBlock at that location, the single document ID is written to the term dictionary.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Termindex"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Index</b>
+ *       <p>The .tip file contains an index into the term dictionary, so that it can be accessed
+ *       randomly. See {@link Lucene90BlockTreeTermsWriter} for more details on the format.
+ * </dl>
+ *
+ * <a id="Frequencies"></a>
+ *
+ * <dl>
+ *   <dd><b>Frequencies and Skip Data</b>
+ *       <p>The .doc file contains the lists of documents which contain each term, along with the
+ *       frequency of the term in that document (except when frequencies are omitted: {@link
+ *       IndexOptions#DOCS}). It also saves skip data to the beginning of each packed or VInt block,
+ *       when the length of document list is larger than packed block size.
+ *       <ul>
+ *         <li>docFile(.doc) --&gt; Header, &lt;TermFreqs, SkipData?&gt;<sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermFreqs --&gt; &lt;PackedBlock&gt; <sup>PackedDocBlockNum</sup>, VIntBlock?
+ *         <li>PackedBlock --&gt; PackedDocDeltaBlock, PackedFreqBlock?
+ *         <li>VIntBlock --&gt; &lt;DocDelta[,
+ *             Freq?]&gt;<sup>DocFreq-PackedBlockSize*PackedDocBlockNum</sup>
+ *         <li>SkipData --&gt; &lt;&lt;SkipLevelLength, SkipLevel&gt; <sup>NumSkipLevels-1</sup>,
+ *             SkipLevel&gt;, SkipDatum?
+ *         <li>SkipLevel --&gt; &lt;SkipDatum&gt; <sup>TrimmedDocFreq/(PackedBlockSize^(Level +
+ *             1))</sup>
+ *         <li>SkipDatum --&gt; DocSkip, DocFPSkip, &lt;PosFPSkip, PosBlockOffset, PayLength?,
+ *             PayFPSkip?&gt;?, ImpactLength, &lt;CompetitiveFreqDelta, CompetitiveNormDelta?&gt;
+ *             <sup>ImpactCount</sup>, SkipChildLevelPointer?
+ *         <li>PackedDocDeltaBlock, PackedFreqBlock --&gt; {@link PackedInts PackedInts}
+ *         <li>DocDelta, Freq, DocSkip, DocFPSkip, PosFPSkip, PosBlockOffset, PayByteUpto,
+ *             PayFPSkip, ImpactLength, CompetitiveFreqDelta --&gt; {@link DataOutput#writeVInt
+ *             VInt}
+ *         <li>CompetitiveNormDelta --&gt; {@link DataOutput#writeZLong ZLong}
+ *         <li>SkipChildLevelPointer --&gt; {@link DataOutput#writeVLong VLong}
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>PackedDocDeltaBlock is theoretically generated from two steps:
+ *             <ol>
+ *               <li>Calculate the difference between each document number and previous one, and get
+ *                   a d-gaps list (for the first document, use absolute value);
+ *               <li>For those d-gaps from first one to
+ *                   PackedDocBlockNum*PackedBlockSize<sup>th</sup>, separately encode as packed
+ *                   blocks.
+ *             </ol>
+ *             If frequencies are not omitted, PackedFreqBlock will be generated without d-gap step.
+ *         <li>VIntBlock stores remaining d-gaps (along with frequencies when possible) with a
+ *             format that encodes DocDelta and Freq:
+ *             <p>DocDelta: if frequencies are indexed, this determines both the document number and
+ *             the frequency. In particular, DocDelta/2 is the difference between this document
+ *             number and the previous document number (or zero when this is the first document in a
+ *             TermFreqs). When DocDelta is odd, the frequency is one. When DocDelta is even, the
+ *             frequency is read as another VInt. If frequencies are omitted, DocDelta contains the
+ *             gap (not multiplied by 2) between document numbers and no frequency information is
+ *             stored.
+ *             <p>For example, the TermFreqs for a term which occurs once in document seven and
+ *             three times in document eleven, with frequencies indexed, would be the following
+ *             sequence of VInts:
+ *             <p>15, 8, 3
+ *             <p>If frequencies were omitted ({@link IndexOptions#DOCS}) it would be this sequence
+ *             of VInts instead:
+ *             <p>7,4
+ *         <li>PackedDocBlockNum is the number of packed blocks for current term's docids or
+ *             frequencies. In particular, PackedDocBlockNum = floor(DocFreq/PackedBlockSize)
+ *         <li>TrimmedDocFreq = DocFreq % PackedBlockSize == 0 ? DocFreq - 1 : DocFreq. We use this
+ *             trick since the definition of skip entry is a little different from base interface.
+ *             In {@link MultiLevelSkipListWriter}, skip data is assumed to be saved for
+ *             skipInterval<sup>th</sup>, 2*skipInterval<sup>th</sup> ... posting in the list.
+ *             However, in Lucene99PostingsFormat, the skip data is saved for
+ *             skipInterval+1<sup>th</sup>, 2*skipInterval+1<sup>th</sup> ... posting
+ *             (skipInterval==PackedBlockSize in this case). When DocFreq is multiple of
+ *             PackedBlockSize, MultiLevelSkipListWriter will expect one more skip data than
+ *             Lucene90SkipWriter.
+ *         <li>SkipDatum is the metadata of one skip entry. For the first block (no matter packed or
+ *             VInt), it is omitted.
+ *         <li>DocSkip records the document number of every PackedBlockSize<sup>th</sup> document
+ *             number in the postings (i.e. last document number in each packed block). On disk it
+ *             is stored as the difference from previous value in the sequence.
+ *         <li>DocFPSkip records the file offsets of each block (excluding )posting at
+ *             PackedBlockSize+1<sup>th</sup>, 2*PackedBlockSize+1<sup>th</sup> ... , in DocFile.
+ *             The file offsets are relative to the start of current term's TermFreqs. On disk it is
+ *             also stored as the difference from previous SkipDatum in the sequence.
+ *         <li>Since positions and payloads are also block encoded, the skip should skip to related
+ *             block first, then fetch the values according to in-block offset. PosFPSkip and
+ *             PayFPSkip record the file offsets of related block in .pos and .pay, respectively.
+ *             While PosBlockOffset indicates which value to fetch inside the related block
+ *             (PayBlockOffset is unnecessary since it is always equal to PosBlockOffset). Same as
+ *             DocFPSkip, the file offsets are relative to the start of current term's TermFreqs,
+ *             and stored as a difference sequence.
+ *         <li>PayByteUpto indicates the start offset of the current payload. It is equivalent to
+ *             the sum of the payload lengths in the current block up to PosBlockOffset
+ *         <li>ImpactLength is the total length of CompetitiveFreqDelta and CompetitiveNormDelta
+ *             pairs. CompetitiveFreqDelta and CompetitiveNormDelta are used to safely skip score
+ *             calculation for uncompetitive documents; See {@link
+ *             org.apache.lucene.codecs.CompetitiveImpactAccumulator} for more details.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Positions"></a>
+ *
+ * <dl>
+ *   <dd><b>Positions</b>
+ *       <p>The .pos file contains the lists of positions that each term occurs at within documents.
+ *       It also sometimes stores part of payloads and offsets for speedup.
+ *       <ul>
+ *         <li>PosFile(.pos) --&gt; Header, &lt;TermPositions&gt; <sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermPositions --&gt; &lt;PackedPosDeltaBlock&gt; <sup>PackedPosBlockNum</sup>,
+ *             VIntBlock?
+ *         <li>VIntBlock --&gt; &lt;PositionDelta[, PayloadLength?], PayloadData?, OffsetDelta?,
+ *             OffsetLength?&gt;<sup>PosVIntCount</sup>
+ *         <li>PackedPosDeltaBlock --&gt; {@link PackedInts PackedInts}
+ *         <li>PositionDelta, OffsetDelta, OffsetLength --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>PayloadData --&gt; {@link DataOutput#writeByte byte}<sup>PayLength</sup>
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>TermPositions are order by term (terms are implicit, from the term dictionary), and
+ *             position values for each term document pair are incremental, and ordered by document
+ *             number.
+ *         <li>PackedPosBlockNum is the number of packed blocks for current term's positions,
+ *             payloads or offsets. In particular, PackedPosBlockNum =
+ *             floor(totalTermFreq/PackedBlockSize)
+ *         <li>PosVIntCount is the number of positions encoded as VInt format. In particular,
+ *             PosVIntCount = totalTermFreq - PackedPosBlockNum*PackedBlockSize
+ *         <li>The procedure how PackedPosDeltaBlock is generated is the same as PackedDocDeltaBlock
+ *             in chapter <a href="#Frequencies">Frequencies and Skip Data</a>.
+ *         <li>PositionDelta is, if payloads are disabled for the term's field, the difference
+ *             between the position of the current occurrence in the document and the previous
+ *             occurrence (or zero, if this is the first occurrence in this document). If payloads
+ *             are enabled for the term's field, then PositionDelta/2 is the difference between the
+ *             current and the previous position. If payloads are enabled and PositionDelta is odd,
+ *             then PayloadLength is stored, indicating the length of the payload at the current
+ *             term position.
+ *         <li>For example, the TermPositions for a term which occurs as the fourth term in one
+ *             document, and as the fifth and ninth term in a subsequent document, would be the
+ *             following sequence of VInts (payloads disabled):
+ *             <p>4, 5, 4
+ *         <li>PayloadData is metadata associated with the current term position. If PayloadLength
+ *             is stored at the current position, then it indicates the length of this payload. If
+ *             PayloadLength is not stored, then this payload has the same length as the payload at
+ *             the previous position.
+ *         <li>OffsetDelta/2 is the difference between this position's startOffset from the previous
+ *             occurrence (or zero, if this is the first occurrence in this document). If
+ *             OffsetDelta is odd, then the length (endOffset-startOffset) differs from the previous
+ *             occurrence and an OffsetLength follows. Offset data is only written for {@link
+ *             IndexOptions#DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS}.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Payloads"></a>
+ *
+ * <dl>
+ *   <dd><b>Payloads and Offsets</b>
+ *       <p>The .pay file will store payloads and offsets associated with certain term-document
+ *       positions. Some payloads and offsets will be separated out into .pos file, for performance
+ *       reasons.
+ *       <ul>
+ *         <li>PayFile(.pay): --&gt; Header, &lt;TermPayloads?, TermOffsets?&gt;
+ *             <sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermPayloads --&gt; &lt;PackedPayLengthBlock, SumPayLength, PayData&gt;
+ *             <sup>PackedPayBlockNum</sup>
+ *         <li>TermOffsets --&gt; &lt;PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock&gt;
+ *             <sup>PackedPayBlockNum</sup>
+ *         <li>PackedPayLengthBlock, PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock --&gt;
+ *             {@link PackedInts PackedInts}
+ *         <li>SumPayLength --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>PayData --&gt; {@link DataOutput#writeByte byte}<sup>SumPayLength</sup>
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>The order of TermPayloads/TermOffsets will be the same as TermPositions, note that
+ *             part of payload/offsets are stored in .pos.
+ *         <li>The procedure how PackedPayLengthBlock and PackedOffsetLengthBlock are generated is
+ *             the same as PackedFreqBlock in chapter <a href="#Frequencies">Frequencies and Skip
+ *             Data</a>. While PackedStartDeltaBlock follows a same procedure as
+ *             PackedDocDeltaBlock.
+ *         <li>PackedPayBlockNum is always equal to PackedPosBlockNum, for the same term. It is also
+ *             synonym for PackedOffsetBlockNum.
+ *         <li>SumPayLength is the total length of payloads written within one block, should be the
+ *             sum of PayLengths in one packed block.
+ *         <li>PayLength in PackedPayLengthBlock is the length of each payload associated with the
+ *             current position.
+ *       </ul>
+ * </dl>
+ *
+ * @lucene.experimental
+ */
+public final class Lucene99PostingsFormat extends PostingsFormat {
+
+  /**
+   * Filename extension for document number, frequencies, and skip data. See chapter: <a
+   * href="#Frequencies">Frequencies and Skip Data</a>
+   */
+  public static final String DOC_EXTENSION = "doc";
+
+  /** Filename extension for positions. See chapter: <a href="#Positions">Positions</a> */
+  public static final String POS_EXTENSION = "pos";
+
+  /**
+   * Filename extension for payloads and offsets. See chapter: <a href="#Payloads">Payloads and
+   * Offsets</a>
+   */
+  public static final String PAY_EXTENSION = "pay";
+
+  /** Size of blocks. */
+  public static final int BLOCK_SIZE = ForUtil.BLOCK_SIZE;
+
+  /**
+   * Expert: The maximum number of skip levels. Smaller values result in slightly smaller indexes,
+   * but slower skipping in big posting lists.
+   */
+  static final int MAX_SKIP_LEVELS = 10;
+
+  static final String TERMS_CODEC = "Lucene90PostingsWriterTerms";
+  static final String DOC_CODEC = "Lucene90PostingsWriterDoc";

Review Comment:
   ```suggestion
     static final String DOC_CODEC = "Lucene99PostingsWriterDoc";
   ```



##########
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99PostingsFormat.java:
##########
@@ -0,0 +1,518 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene99;
+
+import java.io.IOException;
+import org.apache.lucene.codecs.BlockTermState;
+import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.codecs.FieldsConsumer;
+import org.apache.lucene.codecs.FieldsProducer;
+import org.apache.lucene.codecs.MultiLevelSkipListWriter;
+import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.codecs.PostingsReaderBase;
+import org.apache.lucene.codecs.PostingsWriterBase;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsReader;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsWriter;
+import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.SegmentReadState;
+import org.apache.lucene.index.SegmentWriteState;
+import org.apache.lucene.index.TermState;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.IOUtils;
+import org.apache.lucene.util.packed.PackedInts;
+
+/**
+ * Lucene 5.0 postings format, which encodes postings in packed integer blocks for fast decode.
+ *
+ * <p>Basic idea:
+ *
+ * <ul>
+ *   <li><b>Packed Blocks and VInt Blocks</b>:
+ *       <p>In packed blocks, integers are encoded with the same bit width ({@link PackedInts packed
+ *       format}): the block size (i.e. number of integers inside block) is fixed (currently 128).
+ *       Additionally blocks that are all the same value are encoded in an optimized way.
+ *       <p>In VInt blocks, integers are encoded as {@link DataOutput#writeVInt VInt}: the block
+ *       size is variable.
+ *   <li><b>Block structure</b>:
+ *       <p>When the postings are long enough, Lucene99PostingsFormat will try to encode most
+ *       integer data as a packed block.
+ *       <p>Take a term with 259 documents as an example, the first 256 document ids are encoded as
+ *       two packed blocks, while the remaining 3 are encoded as one VInt block.
+ *       <p>Different kinds of data are always encoded separately into different packed blocks, but
+ *       may possibly be interleaved into the same VInt block.
+ *       <p>This strategy is applied to pairs: &lt;document number, frequency&gt;, &lt;position,
+ *       payload length&gt;, &lt;position, offset start, offset length&gt;, and &lt;position,
+ *       payload length, offsetstart, offset length&gt;.
+ *   <li><b>Skipdata settings</b>:
+ *       <p>The structure of skip table is quite similar to previous version of Lucene. Skip
+ *       interval is the same as block size, and each skip entry points to the beginning of each
+ *       block. However, for the first block, skip data is omitted.
+ *   <li><b>Positions, Payloads, and Offsets</b>:
+ *       <p>A position is an integer indicating where the term occurs within one document. A payload
+ *       is a blob of metadata associated with current position. An offset is a pair of integers
+ *       indicating the tokenized start/end offsets for given term in current position: it is
+ *       essentially a specialized payload.
+ *       <p>When payloads and offsets are not omitted, numPositions==numPayloads==numOffsets
+ *       (assuming a null payload contributes one count). As mentioned in block structure, it is
+ *       possible to encode these three either combined or separately.
+ *       <p>In all cases, payloads and offsets are stored together. When encoded as a packed block,
+ *       position data is separated out as .pos, while payloads and offsets are encoded in .pay
+ *       (payload metadata will also be stored directly in .pay). When encoded as VInt blocks, all
+ *       these three are stored interleaved into the .pos (so is payload metadata).
+ *       <p>With this strategy, the majority of payload and offset data will be outside .pos file.
+ *       So for queries that require only position data, running on a full index with payloads and
+ *       offsets, this reduces disk pre-fetches.
+ * </ul>
+ *
+ * <p>Files and detailed format:
+ *
+ * <ul>
+ *   <li><code>.tim</code>: <a href="#Termdictionary">Term Dictionary</a>
+ *   <li><code>.tip</code>: <a href="#Termindex">Term Index</a>
+ *   <li><code>.doc</code>: <a href="#Frequencies">Frequencies and Skip Data</a>
+ *   <li><code>.pos</code>: <a href="#Positions">Positions</a>
+ *   <li><code>.pay</code>: <a href="#Payloads">Payloads and Offsets</a>
+ * </ul>
+ *
+ * <a id="Termdictionary"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Dictionary</b>
+ *       <p>The .tim file contains the list of terms in each field along with per-term statistics
+ *       (such as docfreq) and pointers to the frequencies, positions, payload and skip data in the
+ *       .doc, .pos, and .pay files. See {@link Lucene90BlockTreeTermsWriter} for more details on
+ *       the format.
+ *       <p>NOTE: The term dictionary can plug into different postings implementations: the postings
+ *       writer/reader are actually responsible for encoding and decoding the PostingsHeader and
+ *       TermMetadata sections described here:
+ *       <ul>
+ *         <li>PostingsHeader --&gt; Header, PackedBlockSize
+ *         <li>TermMetadata --&gt; (DocFPDelta|SingletonDocID), PosFPDelta?, PosVIntBlockFPDelta?,
+ *             PayFPDelta?, SkipFPDelta?
+ *         <li>Header, --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>PackedBlockSize, SingletonDocID --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>DocFPDelta, PosFPDelta, PayFPDelta, PosVIntBlockFPDelta, SkipFPDelta --&gt; {@link
+ *             DataOutput#writeVLong VLong}
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>Header is a {@link CodecUtil#writeIndexHeader IndexHeader} storing the version
+ *             information for the postings.
+ *         <li>PackedBlockSize is the fixed block size for packed blocks. In packed block, bit width
+ *             is determined by the largest integer. Smaller block size result in smaller variance
+ *             among width of integers hence smaller indexes. Larger block size result in more
+ *             efficient bulk i/o hence better acceleration. This value should always be a multiple
+ *             of 64, currently fixed as 128 as a tradeoff. It is also the skip interval used to
+ *             accelerate {@link org.apache.lucene.index.PostingsEnum#advance(int)}.
+ *         <li>DocFPDelta determines the position of this term's TermFreqs within the .doc file. In
+ *             particular, it is the difference of file offset between this term's data and previous
+ *             term's data (or zero, for the first term in the block).On disk it is stored as the
+ *             difference from previous value in sequence.
+ *         <li>PosFPDelta determines the position of this term's TermPositions within the .pos file.
+ *             While PayFPDelta determines the position of this term's &lt;TermPayloads,
+ *             TermOffsets?&gt; within the .pay file. Similar to DocFPDelta, it is the difference
+ *             between two file positions (or neglected, for fields that omit payloads and offsets).
+ *         <li>PosVIntBlockFPDelta determines the position of this term's last TermPosition in last
+ *             pos packed block within the .pos file. It is synonym for PayVIntBlockFPDelta or
+ *             OffsetVIntBlockFPDelta. This is actually used to indicate whether it is necessary to
+ *             load following payloads and offsets from .pos instead of .pay. Every time a new block
+ *             of positions are to be loaded, the PostingsReader will use this value to check
+ *             whether current block is packed format or VInt. When packed format, payloads and
+ *             offsets are fetched from .pay, otherwise from .pos. (this value is neglected when
+ *             total number of positions i.e. totalTermFreq is less or equal to PackedBlockSize).
+ *         <li>SkipFPDelta determines the position of this term's SkipData within the .doc file. In
+ *             particular, it is the length of the TermFreq data. SkipDelta is only stored if
+ *             DocFreq is not smaller than SkipMinimum (i.e. 128 in Lucene99PostingsFormat).
+ *         <li>SingletonDocID is an optimization when a term only appears in one document. In this
+ *             case, instead of writing a file pointer to the .doc file (DocFPDelta), and then a
+ *             VIntBlock at that location, the single document ID is written to the term dictionary.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Termindex"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Index</b>
+ *       <p>The .tip file contains an index into the term dictionary, so that it can be accessed
+ *       randomly. See {@link Lucene90BlockTreeTermsWriter} for more details on the format.
+ * </dl>
+ *
+ * <a id="Frequencies"></a>
+ *
+ * <dl>
+ *   <dd><b>Frequencies and Skip Data</b>
+ *       <p>The .doc file contains the lists of documents which contain each term, along with the
+ *       frequency of the term in that document (except when frequencies are omitted: {@link
+ *       IndexOptions#DOCS}). It also saves skip data to the beginning of each packed or VInt block,
+ *       when the length of document list is larger than packed block size.
+ *       <ul>
+ *         <li>docFile(.doc) --&gt; Header, &lt;TermFreqs, SkipData?&gt;<sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermFreqs --&gt; &lt;PackedBlock&gt; <sup>PackedDocBlockNum</sup>, VIntBlock?
+ *         <li>PackedBlock --&gt; PackedDocDeltaBlock, PackedFreqBlock?
+ *         <li>VIntBlock --&gt; &lt;DocDelta[,
+ *             Freq?]&gt;<sup>DocFreq-PackedBlockSize*PackedDocBlockNum</sup>
+ *         <li>SkipData --&gt; &lt;&lt;SkipLevelLength, SkipLevel&gt; <sup>NumSkipLevels-1</sup>,
+ *             SkipLevel&gt;, SkipDatum?
+ *         <li>SkipLevel --&gt; &lt;SkipDatum&gt; <sup>TrimmedDocFreq/(PackedBlockSize^(Level +
+ *             1))</sup>
+ *         <li>SkipDatum --&gt; DocSkip, DocFPSkip, &lt;PosFPSkip, PosBlockOffset, PayLength?,
+ *             PayFPSkip?&gt;?, ImpactLength, &lt;CompetitiveFreqDelta, CompetitiveNormDelta?&gt;
+ *             <sup>ImpactCount</sup>, SkipChildLevelPointer?
+ *         <li>PackedDocDeltaBlock, PackedFreqBlock --&gt; {@link PackedInts PackedInts}
+ *         <li>DocDelta, Freq, DocSkip, DocFPSkip, PosFPSkip, PosBlockOffset, PayByteUpto,
+ *             PayFPSkip, ImpactLength, CompetitiveFreqDelta --&gt; {@link DataOutput#writeVInt
+ *             VInt}
+ *         <li>CompetitiveNormDelta --&gt; {@link DataOutput#writeZLong ZLong}
+ *         <li>SkipChildLevelPointer --&gt; {@link DataOutput#writeVLong VLong}
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>PackedDocDeltaBlock is theoretically generated from two steps:
+ *             <ol>
+ *               <li>Calculate the difference between each document number and previous one, and get
+ *                   a d-gaps list (for the first document, use absolute value);
+ *               <li>For those d-gaps from first one to
+ *                   PackedDocBlockNum*PackedBlockSize<sup>th</sup>, separately encode as packed
+ *                   blocks.
+ *             </ol>
+ *             If frequencies are not omitted, PackedFreqBlock will be generated without d-gap step.
+ *         <li>VIntBlock stores remaining d-gaps (along with frequencies when possible) with a
+ *             format that encodes DocDelta and Freq:
+ *             <p>DocDelta: if frequencies are indexed, this determines both the document number and
+ *             the frequency. In particular, DocDelta/2 is the difference between this document
+ *             number and the previous document number (or zero when this is the first document in a
+ *             TermFreqs). When DocDelta is odd, the frequency is one. When DocDelta is even, the
+ *             frequency is read as another VInt. If frequencies are omitted, DocDelta contains the
+ *             gap (not multiplied by 2) between document numbers and no frequency information is
+ *             stored.
+ *             <p>For example, the TermFreqs for a term which occurs once in document seven and
+ *             three times in document eleven, with frequencies indexed, would be the following
+ *             sequence of VInts:
+ *             <p>15, 8, 3
+ *             <p>If frequencies were omitted ({@link IndexOptions#DOCS}) it would be this sequence
+ *             of VInts instead:
+ *             <p>7,4
+ *         <li>PackedDocBlockNum is the number of packed blocks for current term's docids or
+ *             frequencies. In particular, PackedDocBlockNum = floor(DocFreq/PackedBlockSize)
+ *         <li>TrimmedDocFreq = DocFreq % PackedBlockSize == 0 ? DocFreq - 1 : DocFreq. We use this
+ *             trick since the definition of skip entry is a little different from base interface.
+ *             In {@link MultiLevelSkipListWriter}, skip data is assumed to be saved for
+ *             skipInterval<sup>th</sup>, 2*skipInterval<sup>th</sup> ... posting in the list.
+ *             However, in Lucene99PostingsFormat, the skip data is saved for
+ *             skipInterval+1<sup>th</sup>, 2*skipInterval+1<sup>th</sup> ... posting
+ *             (skipInterval==PackedBlockSize in this case). When DocFreq is multiple of
+ *             PackedBlockSize, MultiLevelSkipListWriter will expect one more skip data than
+ *             Lucene90SkipWriter.
+ *         <li>SkipDatum is the metadata of one skip entry. For the first block (no matter packed or
+ *             VInt), it is omitted.
+ *         <li>DocSkip records the document number of every PackedBlockSize<sup>th</sup> document
+ *             number in the postings (i.e. last document number in each packed block). On disk it
+ *             is stored as the difference from previous value in the sequence.
+ *         <li>DocFPSkip records the file offsets of each block (excluding )posting at
+ *             PackedBlockSize+1<sup>th</sup>, 2*PackedBlockSize+1<sup>th</sup> ... , in DocFile.
+ *             The file offsets are relative to the start of current term's TermFreqs. On disk it is
+ *             also stored as the difference from previous SkipDatum in the sequence.
+ *         <li>Since positions and payloads are also block encoded, the skip should skip to related
+ *             block first, then fetch the values according to in-block offset. PosFPSkip and
+ *             PayFPSkip record the file offsets of related block in .pos and .pay, respectively.
+ *             While PosBlockOffset indicates which value to fetch inside the related block
+ *             (PayBlockOffset is unnecessary since it is always equal to PosBlockOffset). Same as
+ *             DocFPSkip, the file offsets are relative to the start of current term's TermFreqs,
+ *             and stored as a difference sequence.
+ *         <li>PayByteUpto indicates the start offset of the current payload. It is equivalent to
+ *             the sum of the payload lengths in the current block up to PosBlockOffset
+ *         <li>ImpactLength is the total length of CompetitiveFreqDelta and CompetitiveNormDelta
+ *             pairs. CompetitiveFreqDelta and CompetitiveNormDelta are used to safely skip score
+ *             calculation for uncompetitive documents; See {@link
+ *             org.apache.lucene.codecs.CompetitiveImpactAccumulator} for more details.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Positions"></a>
+ *
+ * <dl>
+ *   <dd><b>Positions</b>
+ *       <p>The .pos file contains the lists of positions that each term occurs at within documents.
+ *       It also sometimes stores part of payloads and offsets for speedup.
+ *       <ul>
+ *         <li>PosFile(.pos) --&gt; Header, &lt;TermPositions&gt; <sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermPositions --&gt; &lt;PackedPosDeltaBlock&gt; <sup>PackedPosBlockNum</sup>,
+ *             VIntBlock?
+ *         <li>VIntBlock --&gt; &lt;PositionDelta[, PayloadLength?], PayloadData?, OffsetDelta?,
+ *             OffsetLength?&gt;<sup>PosVIntCount</sup>
+ *         <li>PackedPosDeltaBlock --&gt; {@link PackedInts PackedInts}
+ *         <li>PositionDelta, OffsetDelta, OffsetLength --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>PayloadData --&gt; {@link DataOutput#writeByte byte}<sup>PayLength</sup>
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>TermPositions are order by term (terms are implicit, from the term dictionary), and
+ *             position values for each term document pair are incremental, and ordered by document
+ *             number.
+ *         <li>PackedPosBlockNum is the number of packed blocks for current term's positions,
+ *             payloads or offsets. In particular, PackedPosBlockNum =
+ *             floor(totalTermFreq/PackedBlockSize)
+ *         <li>PosVIntCount is the number of positions encoded as VInt format. In particular,
+ *             PosVIntCount = totalTermFreq - PackedPosBlockNum*PackedBlockSize
+ *         <li>The procedure how PackedPosDeltaBlock is generated is the same as PackedDocDeltaBlock
+ *             in chapter <a href="#Frequencies">Frequencies and Skip Data</a>.
+ *         <li>PositionDelta is, if payloads are disabled for the term's field, the difference
+ *             between the position of the current occurrence in the document and the previous
+ *             occurrence (or zero, if this is the first occurrence in this document). If payloads
+ *             are enabled for the term's field, then PositionDelta/2 is the difference between the
+ *             current and the previous position. If payloads are enabled and PositionDelta is odd,
+ *             then PayloadLength is stored, indicating the length of the payload at the current
+ *             term position.
+ *         <li>For example, the TermPositions for a term which occurs as the fourth term in one
+ *             document, and as the fifth and ninth term in a subsequent document, would be the
+ *             following sequence of VInts (payloads disabled):
+ *             <p>4, 5, 4
+ *         <li>PayloadData is metadata associated with the current term position. If PayloadLength
+ *             is stored at the current position, then it indicates the length of this payload. If
+ *             PayloadLength is not stored, then this payload has the same length as the payload at
+ *             the previous position.
+ *         <li>OffsetDelta/2 is the difference between this position's startOffset from the previous
+ *             occurrence (or zero, if this is the first occurrence in this document). If
+ *             OffsetDelta is odd, then the length (endOffset-startOffset) differs from the previous
+ *             occurrence and an OffsetLength follows. Offset data is only written for {@link
+ *             IndexOptions#DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS}.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Payloads"></a>
+ *
+ * <dl>
+ *   <dd><b>Payloads and Offsets</b>
+ *       <p>The .pay file will store payloads and offsets associated with certain term-document
+ *       positions. Some payloads and offsets will be separated out into .pos file, for performance
+ *       reasons.
+ *       <ul>
+ *         <li>PayFile(.pay): --&gt; Header, &lt;TermPayloads?, TermOffsets?&gt;
+ *             <sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermPayloads --&gt; &lt;PackedPayLengthBlock, SumPayLength, PayData&gt;
+ *             <sup>PackedPayBlockNum</sup>
+ *         <li>TermOffsets --&gt; &lt;PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock&gt;
+ *             <sup>PackedPayBlockNum</sup>
+ *         <li>PackedPayLengthBlock, PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock --&gt;
+ *             {@link PackedInts PackedInts}
+ *         <li>SumPayLength --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>PayData --&gt; {@link DataOutput#writeByte byte}<sup>SumPayLength</sup>
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>The order of TermPayloads/TermOffsets will be the same as TermPositions, note that
+ *             part of payload/offsets are stored in .pos.
+ *         <li>The procedure how PackedPayLengthBlock and PackedOffsetLengthBlock are generated is
+ *             the same as PackedFreqBlock in chapter <a href="#Frequencies">Frequencies and Skip
+ *             Data</a>. While PackedStartDeltaBlock follows a same procedure as
+ *             PackedDocDeltaBlock.
+ *         <li>PackedPayBlockNum is always equal to PackedPosBlockNum, for the same term. It is also
+ *             synonym for PackedOffsetBlockNum.
+ *         <li>SumPayLength is the total length of payloads written within one block, should be the
+ *             sum of PayLengths in one packed block.
+ *         <li>PayLength in PackedPayLengthBlock is the length of each payload associated with the
+ *             current position.
+ *       </ul>
+ * </dl>
+ *
+ * @lucene.experimental
+ */
+public final class Lucene99PostingsFormat extends PostingsFormat {
+
+  /**
+   * Filename extension for document number, frequencies, and skip data. See chapter: <a
+   * href="#Frequencies">Frequencies and Skip Data</a>
+   */
+  public static final String DOC_EXTENSION = "doc";
+
+  /** Filename extension for positions. See chapter: <a href="#Positions">Positions</a> */
+  public static final String POS_EXTENSION = "pos";
+
+  /**
+   * Filename extension for payloads and offsets. See chapter: <a href="#Payloads">Payloads and
+   * Offsets</a>
+   */
+  public static final String PAY_EXTENSION = "pay";
+
+  /** Size of blocks. */
+  public static final int BLOCK_SIZE = ForUtil.BLOCK_SIZE;
+
+  /**
+   * Expert: The maximum number of skip levels. Smaller values result in slightly smaller indexes,
+   * but slower skipping in big posting lists.
+   */
+  static final int MAX_SKIP_LEVELS = 10;
+
+  static final String TERMS_CODEC = "Lucene90PostingsWriterTerms";
+  static final String DOC_CODEC = "Lucene90PostingsWriterDoc";
+  static final String POS_CODEC = "Lucene90PostingsWriterPos";

Review Comment:
   ```suggestion
     static final String POS_CODEC = "Lucene99PostingsWriterPos";
   ```



##########
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99PostingsFormat.java:
##########
@@ -0,0 +1,518 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene99;
+
+import java.io.IOException;
+import org.apache.lucene.codecs.BlockTermState;
+import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.codecs.FieldsConsumer;
+import org.apache.lucene.codecs.FieldsProducer;
+import org.apache.lucene.codecs.MultiLevelSkipListWriter;
+import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.codecs.PostingsReaderBase;
+import org.apache.lucene.codecs.PostingsWriterBase;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsReader;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsWriter;
+import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.SegmentReadState;
+import org.apache.lucene.index.SegmentWriteState;
+import org.apache.lucene.index.TermState;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.IOUtils;
+import org.apache.lucene.util.packed.PackedInts;
+
+/**
+ * Lucene 5.0 postings format, which encodes postings in packed integer blocks for fast decode.
+ *
+ * <p>Basic idea:
+ *
+ * <ul>
+ *   <li><b>Packed Blocks and VInt Blocks</b>:
+ *       <p>In packed blocks, integers are encoded with the same bit width ({@link PackedInts packed
+ *       format}): the block size (i.e. number of integers inside block) is fixed (currently 128).
+ *       Additionally blocks that are all the same value are encoded in an optimized way.
+ *       <p>In VInt blocks, integers are encoded as {@link DataOutput#writeVInt VInt}: the block
+ *       size is variable.
+ *   <li><b>Block structure</b>:
+ *       <p>When the postings are long enough, Lucene99PostingsFormat will try to encode most
+ *       integer data as a packed block.
+ *       <p>Take a term with 259 documents as an example, the first 256 document ids are encoded as
+ *       two packed blocks, while the remaining 3 are encoded as one VInt block.
+ *       <p>Different kinds of data are always encoded separately into different packed blocks, but
+ *       may possibly be interleaved into the same VInt block.
+ *       <p>This strategy is applied to pairs: &lt;document number, frequency&gt;, &lt;position,
+ *       payload length&gt;, &lt;position, offset start, offset length&gt;, and &lt;position,
+ *       payload length, offsetstart, offset length&gt;.
+ *   <li><b>Skipdata settings</b>:
+ *       <p>The structure of skip table is quite similar to previous version of Lucene. Skip
+ *       interval is the same as block size, and each skip entry points to the beginning of each
+ *       block. However, for the first block, skip data is omitted.
+ *   <li><b>Positions, Payloads, and Offsets</b>:
+ *       <p>A position is an integer indicating where the term occurs within one document. A payload
+ *       is a blob of metadata associated with current position. An offset is a pair of integers
+ *       indicating the tokenized start/end offsets for given term in current position: it is
+ *       essentially a specialized payload.
+ *       <p>When payloads and offsets are not omitted, numPositions==numPayloads==numOffsets
+ *       (assuming a null payload contributes one count). As mentioned in block structure, it is
+ *       possible to encode these three either combined or separately.
+ *       <p>In all cases, payloads and offsets are stored together. When encoded as a packed block,
+ *       position data is separated out as .pos, while payloads and offsets are encoded in .pay
+ *       (payload metadata will also be stored directly in .pay). When encoded as VInt blocks, all
+ *       these three are stored interleaved into the .pos (so is payload metadata).
+ *       <p>With this strategy, the majority of payload and offset data will be outside .pos file.
+ *       So for queries that require only position data, running on a full index with payloads and
+ *       offsets, this reduces disk pre-fetches.
+ * </ul>
+ *
+ * <p>Files and detailed format:
+ *
+ * <ul>
+ *   <li><code>.tim</code>: <a href="#Termdictionary">Term Dictionary</a>
+ *   <li><code>.tip</code>: <a href="#Termindex">Term Index</a>
+ *   <li><code>.doc</code>: <a href="#Frequencies">Frequencies and Skip Data</a>
+ *   <li><code>.pos</code>: <a href="#Positions">Positions</a>
+ *   <li><code>.pay</code>: <a href="#Payloads">Payloads and Offsets</a>
+ * </ul>
+ *
+ * <a id="Termdictionary"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Dictionary</b>
+ *       <p>The .tim file contains the list of terms in each field along with per-term statistics
+ *       (such as docfreq) and pointers to the frequencies, positions, payload and skip data in the
+ *       .doc, .pos, and .pay files. See {@link Lucene90BlockTreeTermsWriter} for more details on
+ *       the format.
+ *       <p>NOTE: The term dictionary can plug into different postings implementations: the postings
+ *       writer/reader are actually responsible for encoding and decoding the PostingsHeader and
+ *       TermMetadata sections described here:
+ *       <ul>
+ *         <li>PostingsHeader --&gt; Header, PackedBlockSize
+ *         <li>TermMetadata --&gt; (DocFPDelta|SingletonDocID), PosFPDelta?, PosVIntBlockFPDelta?,
+ *             PayFPDelta?, SkipFPDelta?
+ *         <li>Header, --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>PackedBlockSize, SingletonDocID --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>DocFPDelta, PosFPDelta, PayFPDelta, PosVIntBlockFPDelta, SkipFPDelta --&gt; {@link
+ *             DataOutput#writeVLong VLong}
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>Header is a {@link CodecUtil#writeIndexHeader IndexHeader} storing the version
+ *             information for the postings.
+ *         <li>PackedBlockSize is the fixed block size for packed blocks. In packed block, bit width
+ *             is determined by the largest integer. Smaller block size result in smaller variance
+ *             among width of integers hence smaller indexes. Larger block size result in more
+ *             efficient bulk i/o hence better acceleration. This value should always be a multiple
+ *             of 64, currently fixed as 128 as a tradeoff. It is also the skip interval used to
+ *             accelerate {@link org.apache.lucene.index.PostingsEnum#advance(int)}.
+ *         <li>DocFPDelta determines the position of this term's TermFreqs within the .doc file. In
+ *             particular, it is the difference of file offset between this term's data and previous
+ *             term's data (or zero, for the first term in the block).On disk it is stored as the
+ *             difference from previous value in sequence.
+ *         <li>PosFPDelta determines the position of this term's TermPositions within the .pos file.
+ *             While PayFPDelta determines the position of this term's &lt;TermPayloads,
+ *             TermOffsets?&gt; within the .pay file. Similar to DocFPDelta, it is the difference
+ *             between two file positions (or neglected, for fields that omit payloads and offsets).
+ *         <li>PosVIntBlockFPDelta determines the position of this term's last TermPosition in last
+ *             pos packed block within the .pos file. It is synonym for PayVIntBlockFPDelta or
+ *             OffsetVIntBlockFPDelta. This is actually used to indicate whether it is necessary to
+ *             load following payloads and offsets from .pos instead of .pay. Every time a new block
+ *             of positions are to be loaded, the PostingsReader will use this value to check
+ *             whether current block is packed format or VInt. When packed format, payloads and
+ *             offsets are fetched from .pay, otherwise from .pos. (this value is neglected when
+ *             total number of positions i.e. totalTermFreq is less or equal to PackedBlockSize).
+ *         <li>SkipFPDelta determines the position of this term's SkipData within the .doc file. In
+ *             particular, it is the length of the TermFreq data. SkipDelta is only stored if
+ *             DocFreq is not smaller than SkipMinimum (i.e. 128 in Lucene99PostingsFormat).
+ *         <li>SingletonDocID is an optimization when a term only appears in one document. In this
+ *             case, instead of writing a file pointer to the .doc file (DocFPDelta), and then a
+ *             VIntBlock at that location, the single document ID is written to the term dictionary.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Termindex"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Index</b>
+ *       <p>The .tip file contains an index into the term dictionary, so that it can be accessed
+ *       randomly. See {@link Lucene90BlockTreeTermsWriter} for more details on the format.
+ * </dl>
+ *
+ * <a id="Frequencies"></a>
+ *
+ * <dl>
+ *   <dd><b>Frequencies and Skip Data</b>
+ *       <p>The .doc file contains the lists of documents which contain each term, along with the
+ *       frequency of the term in that document (except when frequencies are omitted: {@link
+ *       IndexOptions#DOCS}). It also saves skip data to the beginning of each packed or VInt block,
+ *       when the length of document list is larger than packed block size.
+ *       <ul>
+ *         <li>docFile(.doc) --&gt; Header, &lt;TermFreqs, SkipData?&gt;<sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermFreqs --&gt; &lt;PackedBlock&gt; <sup>PackedDocBlockNum</sup>, VIntBlock?
+ *         <li>PackedBlock --&gt; PackedDocDeltaBlock, PackedFreqBlock?
+ *         <li>VIntBlock --&gt; &lt;DocDelta[,
+ *             Freq?]&gt;<sup>DocFreq-PackedBlockSize*PackedDocBlockNum</sup>
+ *         <li>SkipData --&gt; &lt;&lt;SkipLevelLength, SkipLevel&gt; <sup>NumSkipLevels-1</sup>,
+ *             SkipLevel&gt;, SkipDatum?
+ *         <li>SkipLevel --&gt; &lt;SkipDatum&gt; <sup>TrimmedDocFreq/(PackedBlockSize^(Level +
+ *             1))</sup>
+ *         <li>SkipDatum --&gt; DocSkip, DocFPSkip, &lt;PosFPSkip, PosBlockOffset, PayLength?,
+ *             PayFPSkip?&gt;?, ImpactLength, &lt;CompetitiveFreqDelta, CompetitiveNormDelta?&gt;
+ *             <sup>ImpactCount</sup>, SkipChildLevelPointer?
+ *         <li>PackedDocDeltaBlock, PackedFreqBlock --&gt; {@link PackedInts PackedInts}
+ *         <li>DocDelta, Freq, DocSkip, DocFPSkip, PosFPSkip, PosBlockOffset, PayByteUpto,
+ *             PayFPSkip, ImpactLength, CompetitiveFreqDelta --&gt; {@link DataOutput#writeVInt
+ *             VInt}
+ *         <li>CompetitiveNormDelta --&gt; {@link DataOutput#writeZLong ZLong}
+ *         <li>SkipChildLevelPointer --&gt; {@link DataOutput#writeVLong VLong}
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>PackedDocDeltaBlock is theoretically generated from two steps:
+ *             <ol>
+ *               <li>Calculate the difference between each document number and previous one, and get
+ *                   a d-gaps list (for the first document, use absolute value);
+ *               <li>For those d-gaps from first one to
+ *                   PackedDocBlockNum*PackedBlockSize<sup>th</sup>, separately encode as packed
+ *                   blocks.
+ *             </ol>
+ *             If frequencies are not omitted, PackedFreqBlock will be generated without d-gap step.
+ *         <li>VIntBlock stores remaining d-gaps (along with frequencies when possible) with a
+ *             format that encodes DocDelta and Freq:
+ *             <p>DocDelta: if frequencies are indexed, this determines both the document number and
+ *             the frequency. In particular, DocDelta/2 is the difference between this document
+ *             number and the previous document number (or zero when this is the first document in a
+ *             TermFreqs). When DocDelta is odd, the frequency is one. When DocDelta is even, the
+ *             frequency is read as another VInt. If frequencies are omitted, DocDelta contains the
+ *             gap (not multiplied by 2) between document numbers and no frequency information is
+ *             stored.
+ *             <p>For example, the TermFreqs for a term which occurs once in document seven and
+ *             three times in document eleven, with frequencies indexed, would be the following
+ *             sequence of VInts:
+ *             <p>15, 8, 3
+ *             <p>If frequencies were omitted ({@link IndexOptions#DOCS}) it would be this sequence
+ *             of VInts instead:
+ *             <p>7,4
+ *         <li>PackedDocBlockNum is the number of packed blocks for current term's docids or
+ *             frequencies. In particular, PackedDocBlockNum = floor(DocFreq/PackedBlockSize)
+ *         <li>TrimmedDocFreq = DocFreq % PackedBlockSize == 0 ? DocFreq - 1 : DocFreq. We use this
+ *             trick since the definition of skip entry is a little different from base interface.
+ *             In {@link MultiLevelSkipListWriter}, skip data is assumed to be saved for
+ *             skipInterval<sup>th</sup>, 2*skipInterval<sup>th</sup> ... posting in the list.
+ *             However, in Lucene99PostingsFormat, the skip data is saved for
+ *             skipInterval+1<sup>th</sup>, 2*skipInterval+1<sup>th</sup> ... posting
+ *             (skipInterval==PackedBlockSize in this case). When DocFreq is multiple of
+ *             PackedBlockSize, MultiLevelSkipListWriter will expect one more skip data than
+ *             Lucene90SkipWriter.

Review Comment:
   ```suggestion
    *             Lucene99SkipWriter.
   ```



##########
lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99PostingsFormat.java:
##########
@@ -0,0 +1,518 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene99;
+
+import java.io.IOException;
+import org.apache.lucene.codecs.BlockTermState;
+import org.apache.lucene.codecs.CodecUtil;
+import org.apache.lucene.codecs.FieldsConsumer;
+import org.apache.lucene.codecs.FieldsProducer;
+import org.apache.lucene.codecs.MultiLevelSkipListWriter;
+import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.codecs.PostingsReaderBase;
+import org.apache.lucene.codecs.PostingsWriterBase;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsReader;
+import org.apache.lucene.codecs.lucene90.blocktree.Lucene90BlockTreeTermsWriter;
+import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.SegmentReadState;
+import org.apache.lucene.index.SegmentWriteState;
+import org.apache.lucene.index.TermState;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.IOUtils;
+import org.apache.lucene.util.packed.PackedInts;
+
+/**
+ * Lucene 5.0 postings format, which encodes postings in packed integer blocks for fast decode.
+ *
+ * <p>Basic idea:
+ *
+ * <ul>
+ *   <li><b>Packed Blocks and VInt Blocks</b>:
+ *       <p>In packed blocks, integers are encoded with the same bit width ({@link PackedInts packed
+ *       format}): the block size (i.e. number of integers inside block) is fixed (currently 128).
+ *       Additionally blocks that are all the same value are encoded in an optimized way.
+ *       <p>In VInt blocks, integers are encoded as {@link DataOutput#writeVInt VInt}: the block
+ *       size is variable.
+ *   <li><b>Block structure</b>:
+ *       <p>When the postings are long enough, Lucene99PostingsFormat will try to encode most
+ *       integer data as a packed block.
+ *       <p>Take a term with 259 documents as an example, the first 256 document ids are encoded as
+ *       two packed blocks, while the remaining 3 are encoded as one VInt block.
+ *       <p>Different kinds of data are always encoded separately into different packed blocks, but
+ *       may possibly be interleaved into the same VInt block.
+ *       <p>This strategy is applied to pairs: &lt;document number, frequency&gt;, &lt;position,
+ *       payload length&gt;, &lt;position, offset start, offset length&gt;, and &lt;position,
+ *       payload length, offsetstart, offset length&gt;.
+ *   <li><b>Skipdata settings</b>:
+ *       <p>The structure of skip table is quite similar to previous version of Lucene. Skip
+ *       interval is the same as block size, and each skip entry points to the beginning of each
+ *       block. However, for the first block, skip data is omitted.
+ *   <li><b>Positions, Payloads, and Offsets</b>:
+ *       <p>A position is an integer indicating where the term occurs within one document. A payload
+ *       is a blob of metadata associated with current position. An offset is a pair of integers
+ *       indicating the tokenized start/end offsets for given term in current position: it is
+ *       essentially a specialized payload.
+ *       <p>When payloads and offsets are not omitted, numPositions==numPayloads==numOffsets
+ *       (assuming a null payload contributes one count). As mentioned in block structure, it is
+ *       possible to encode these three either combined or separately.
+ *       <p>In all cases, payloads and offsets are stored together. When encoded as a packed block,
+ *       position data is separated out as .pos, while payloads and offsets are encoded in .pay
+ *       (payload metadata will also be stored directly in .pay). When encoded as VInt blocks, all
+ *       these three are stored interleaved into the .pos (so is payload metadata).
+ *       <p>With this strategy, the majority of payload and offset data will be outside .pos file.
+ *       So for queries that require only position data, running on a full index with payloads and
+ *       offsets, this reduces disk pre-fetches.
+ * </ul>
+ *
+ * <p>Files and detailed format:
+ *
+ * <ul>
+ *   <li><code>.tim</code>: <a href="#Termdictionary">Term Dictionary</a>
+ *   <li><code>.tip</code>: <a href="#Termindex">Term Index</a>
+ *   <li><code>.doc</code>: <a href="#Frequencies">Frequencies and Skip Data</a>
+ *   <li><code>.pos</code>: <a href="#Positions">Positions</a>
+ *   <li><code>.pay</code>: <a href="#Payloads">Payloads and Offsets</a>
+ * </ul>
+ *
+ * <a id="Termdictionary"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Dictionary</b>
+ *       <p>The .tim file contains the list of terms in each field along with per-term statistics
+ *       (such as docfreq) and pointers to the frequencies, positions, payload and skip data in the
+ *       .doc, .pos, and .pay files. See {@link Lucene90BlockTreeTermsWriter} for more details on
+ *       the format.
+ *       <p>NOTE: The term dictionary can plug into different postings implementations: the postings
+ *       writer/reader are actually responsible for encoding and decoding the PostingsHeader and
+ *       TermMetadata sections described here:
+ *       <ul>
+ *         <li>PostingsHeader --&gt; Header, PackedBlockSize
+ *         <li>TermMetadata --&gt; (DocFPDelta|SingletonDocID), PosFPDelta?, PosVIntBlockFPDelta?,
+ *             PayFPDelta?, SkipFPDelta?
+ *         <li>Header, --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>PackedBlockSize, SingletonDocID --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>DocFPDelta, PosFPDelta, PayFPDelta, PosVIntBlockFPDelta, SkipFPDelta --&gt; {@link
+ *             DataOutput#writeVLong VLong}
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>Header is a {@link CodecUtil#writeIndexHeader IndexHeader} storing the version
+ *             information for the postings.
+ *         <li>PackedBlockSize is the fixed block size for packed blocks. In packed block, bit width
+ *             is determined by the largest integer. Smaller block size result in smaller variance
+ *             among width of integers hence smaller indexes. Larger block size result in more
+ *             efficient bulk i/o hence better acceleration. This value should always be a multiple
+ *             of 64, currently fixed as 128 as a tradeoff. It is also the skip interval used to
+ *             accelerate {@link org.apache.lucene.index.PostingsEnum#advance(int)}.
+ *         <li>DocFPDelta determines the position of this term's TermFreqs within the .doc file. In
+ *             particular, it is the difference of file offset between this term's data and previous
+ *             term's data (or zero, for the first term in the block).On disk it is stored as the
+ *             difference from previous value in sequence.
+ *         <li>PosFPDelta determines the position of this term's TermPositions within the .pos file.
+ *             While PayFPDelta determines the position of this term's &lt;TermPayloads,
+ *             TermOffsets?&gt; within the .pay file. Similar to DocFPDelta, it is the difference
+ *             between two file positions (or neglected, for fields that omit payloads and offsets).
+ *         <li>PosVIntBlockFPDelta determines the position of this term's last TermPosition in last
+ *             pos packed block within the .pos file. It is synonym for PayVIntBlockFPDelta or
+ *             OffsetVIntBlockFPDelta. This is actually used to indicate whether it is necessary to
+ *             load following payloads and offsets from .pos instead of .pay. Every time a new block
+ *             of positions are to be loaded, the PostingsReader will use this value to check
+ *             whether current block is packed format or VInt. When packed format, payloads and
+ *             offsets are fetched from .pay, otherwise from .pos. (this value is neglected when
+ *             total number of positions i.e. totalTermFreq is less or equal to PackedBlockSize).
+ *         <li>SkipFPDelta determines the position of this term's SkipData within the .doc file. In
+ *             particular, it is the length of the TermFreq data. SkipDelta is only stored if
+ *             DocFreq is not smaller than SkipMinimum (i.e. 128 in Lucene99PostingsFormat).
+ *         <li>SingletonDocID is an optimization when a term only appears in one document. In this
+ *             case, instead of writing a file pointer to the .doc file (DocFPDelta), and then a
+ *             VIntBlock at that location, the single document ID is written to the term dictionary.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Termindex"></a>
+ *
+ * <dl>
+ *   <dd><b>Term Index</b>
+ *       <p>The .tip file contains an index into the term dictionary, so that it can be accessed
+ *       randomly. See {@link Lucene90BlockTreeTermsWriter} for more details on the format.
+ * </dl>
+ *
+ * <a id="Frequencies"></a>
+ *
+ * <dl>
+ *   <dd><b>Frequencies and Skip Data</b>
+ *       <p>The .doc file contains the lists of documents which contain each term, along with the
+ *       frequency of the term in that document (except when frequencies are omitted: {@link
+ *       IndexOptions#DOCS}). It also saves skip data to the beginning of each packed or VInt block,
+ *       when the length of document list is larger than packed block size.
+ *       <ul>
+ *         <li>docFile(.doc) --&gt; Header, &lt;TermFreqs, SkipData?&gt;<sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermFreqs --&gt; &lt;PackedBlock&gt; <sup>PackedDocBlockNum</sup>, VIntBlock?
+ *         <li>PackedBlock --&gt; PackedDocDeltaBlock, PackedFreqBlock?
+ *         <li>VIntBlock --&gt; &lt;DocDelta[,
+ *             Freq?]&gt;<sup>DocFreq-PackedBlockSize*PackedDocBlockNum</sup>
+ *         <li>SkipData --&gt; &lt;&lt;SkipLevelLength, SkipLevel&gt; <sup>NumSkipLevels-1</sup>,
+ *             SkipLevel&gt;, SkipDatum?
+ *         <li>SkipLevel --&gt; &lt;SkipDatum&gt; <sup>TrimmedDocFreq/(PackedBlockSize^(Level +
+ *             1))</sup>
+ *         <li>SkipDatum --&gt; DocSkip, DocFPSkip, &lt;PosFPSkip, PosBlockOffset, PayLength?,
+ *             PayFPSkip?&gt;?, ImpactLength, &lt;CompetitiveFreqDelta, CompetitiveNormDelta?&gt;
+ *             <sup>ImpactCount</sup>, SkipChildLevelPointer?
+ *         <li>PackedDocDeltaBlock, PackedFreqBlock --&gt; {@link PackedInts PackedInts}
+ *         <li>DocDelta, Freq, DocSkip, DocFPSkip, PosFPSkip, PosBlockOffset, PayByteUpto,
+ *             PayFPSkip, ImpactLength, CompetitiveFreqDelta --&gt; {@link DataOutput#writeVInt
+ *             VInt}
+ *         <li>CompetitiveNormDelta --&gt; {@link DataOutput#writeZLong ZLong}
+ *         <li>SkipChildLevelPointer --&gt; {@link DataOutput#writeVLong VLong}
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>PackedDocDeltaBlock is theoretically generated from two steps:
+ *             <ol>
+ *               <li>Calculate the difference between each document number and previous one, and get
+ *                   a d-gaps list (for the first document, use absolute value);
+ *               <li>For those d-gaps from first one to
+ *                   PackedDocBlockNum*PackedBlockSize<sup>th</sup>, separately encode as packed
+ *                   blocks.
+ *             </ol>
+ *             If frequencies are not omitted, PackedFreqBlock will be generated without d-gap step.
+ *         <li>VIntBlock stores remaining d-gaps (along with frequencies when possible) with a
+ *             format that encodes DocDelta and Freq:
+ *             <p>DocDelta: if frequencies are indexed, this determines both the document number and
+ *             the frequency. In particular, DocDelta/2 is the difference between this document
+ *             number and the previous document number (or zero when this is the first document in a
+ *             TermFreqs). When DocDelta is odd, the frequency is one. When DocDelta is even, the
+ *             frequency is read as another VInt. If frequencies are omitted, DocDelta contains the
+ *             gap (not multiplied by 2) between document numbers and no frequency information is
+ *             stored.
+ *             <p>For example, the TermFreqs for a term which occurs once in document seven and
+ *             three times in document eleven, with frequencies indexed, would be the following
+ *             sequence of VInts:
+ *             <p>15, 8, 3
+ *             <p>If frequencies were omitted ({@link IndexOptions#DOCS}) it would be this sequence
+ *             of VInts instead:
+ *             <p>7,4
+ *         <li>PackedDocBlockNum is the number of packed blocks for current term's docids or
+ *             frequencies. In particular, PackedDocBlockNum = floor(DocFreq/PackedBlockSize)
+ *         <li>TrimmedDocFreq = DocFreq % PackedBlockSize == 0 ? DocFreq - 1 : DocFreq. We use this
+ *             trick since the definition of skip entry is a little different from base interface.
+ *             In {@link MultiLevelSkipListWriter}, skip data is assumed to be saved for
+ *             skipInterval<sup>th</sup>, 2*skipInterval<sup>th</sup> ... posting in the list.
+ *             However, in Lucene99PostingsFormat, the skip data is saved for
+ *             skipInterval+1<sup>th</sup>, 2*skipInterval+1<sup>th</sup> ... posting
+ *             (skipInterval==PackedBlockSize in this case). When DocFreq is multiple of
+ *             PackedBlockSize, MultiLevelSkipListWriter will expect one more skip data than
+ *             Lucene90SkipWriter.
+ *         <li>SkipDatum is the metadata of one skip entry. For the first block (no matter packed or
+ *             VInt), it is omitted.
+ *         <li>DocSkip records the document number of every PackedBlockSize<sup>th</sup> document
+ *             number in the postings (i.e. last document number in each packed block). On disk it
+ *             is stored as the difference from previous value in the sequence.
+ *         <li>DocFPSkip records the file offsets of each block (excluding )posting at
+ *             PackedBlockSize+1<sup>th</sup>, 2*PackedBlockSize+1<sup>th</sup> ... , in DocFile.
+ *             The file offsets are relative to the start of current term's TermFreqs. On disk it is
+ *             also stored as the difference from previous SkipDatum in the sequence.
+ *         <li>Since positions and payloads are also block encoded, the skip should skip to related
+ *             block first, then fetch the values according to in-block offset. PosFPSkip and
+ *             PayFPSkip record the file offsets of related block in .pos and .pay, respectively.
+ *             While PosBlockOffset indicates which value to fetch inside the related block
+ *             (PayBlockOffset is unnecessary since it is always equal to PosBlockOffset). Same as
+ *             DocFPSkip, the file offsets are relative to the start of current term's TermFreqs,
+ *             and stored as a difference sequence.
+ *         <li>PayByteUpto indicates the start offset of the current payload. It is equivalent to
+ *             the sum of the payload lengths in the current block up to PosBlockOffset
+ *         <li>ImpactLength is the total length of CompetitiveFreqDelta and CompetitiveNormDelta
+ *             pairs. CompetitiveFreqDelta and CompetitiveNormDelta are used to safely skip score
+ *             calculation for uncompetitive documents; See {@link
+ *             org.apache.lucene.codecs.CompetitiveImpactAccumulator} for more details.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Positions"></a>
+ *
+ * <dl>
+ *   <dd><b>Positions</b>
+ *       <p>The .pos file contains the lists of positions that each term occurs at within documents.
+ *       It also sometimes stores part of payloads and offsets for speedup.
+ *       <ul>
+ *         <li>PosFile(.pos) --&gt; Header, &lt;TermPositions&gt; <sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermPositions --&gt; &lt;PackedPosDeltaBlock&gt; <sup>PackedPosBlockNum</sup>,
+ *             VIntBlock?
+ *         <li>VIntBlock --&gt; &lt;PositionDelta[, PayloadLength?], PayloadData?, OffsetDelta?,
+ *             OffsetLength?&gt;<sup>PosVIntCount</sup>
+ *         <li>PackedPosDeltaBlock --&gt; {@link PackedInts PackedInts}
+ *         <li>PositionDelta, OffsetDelta, OffsetLength --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>PayloadData --&gt; {@link DataOutput#writeByte byte}<sup>PayLength</sup>
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>TermPositions are order by term (terms are implicit, from the term dictionary), and
+ *             position values for each term document pair are incremental, and ordered by document
+ *             number.
+ *         <li>PackedPosBlockNum is the number of packed blocks for current term's positions,
+ *             payloads or offsets. In particular, PackedPosBlockNum =
+ *             floor(totalTermFreq/PackedBlockSize)
+ *         <li>PosVIntCount is the number of positions encoded as VInt format. In particular,
+ *             PosVIntCount = totalTermFreq - PackedPosBlockNum*PackedBlockSize
+ *         <li>The procedure how PackedPosDeltaBlock is generated is the same as PackedDocDeltaBlock
+ *             in chapter <a href="#Frequencies">Frequencies and Skip Data</a>.
+ *         <li>PositionDelta is, if payloads are disabled for the term's field, the difference
+ *             between the position of the current occurrence in the document and the previous
+ *             occurrence (or zero, if this is the first occurrence in this document). If payloads
+ *             are enabled for the term's field, then PositionDelta/2 is the difference between the
+ *             current and the previous position. If payloads are enabled and PositionDelta is odd,
+ *             then PayloadLength is stored, indicating the length of the payload at the current
+ *             term position.
+ *         <li>For example, the TermPositions for a term which occurs as the fourth term in one
+ *             document, and as the fifth and ninth term in a subsequent document, would be the
+ *             following sequence of VInts (payloads disabled):
+ *             <p>4, 5, 4
+ *         <li>PayloadData is metadata associated with the current term position. If PayloadLength
+ *             is stored at the current position, then it indicates the length of this payload. If
+ *             PayloadLength is not stored, then this payload has the same length as the payload at
+ *             the previous position.
+ *         <li>OffsetDelta/2 is the difference between this position's startOffset from the previous
+ *             occurrence (or zero, if this is the first occurrence in this document). If
+ *             OffsetDelta is odd, then the length (endOffset-startOffset) differs from the previous
+ *             occurrence and an OffsetLength follows. Offset data is only written for {@link
+ *             IndexOptions#DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS}.
+ *       </ul>
+ * </dl>
+ *
+ * <a id="Payloads"></a>
+ *
+ * <dl>
+ *   <dd><b>Payloads and Offsets</b>
+ *       <p>The .pay file will store payloads and offsets associated with certain term-document
+ *       positions. Some payloads and offsets will be separated out into .pos file, for performance
+ *       reasons.
+ *       <ul>
+ *         <li>PayFile(.pay): --&gt; Header, &lt;TermPayloads?, TermOffsets?&gt;
+ *             <sup>TermCount</sup>, Footer
+ *         <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
+ *         <li>TermPayloads --&gt; &lt;PackedPayLengthBlock, SumPayLength, PayData&gt;
+ *             <sup>PackedPayBlockNum</sup>
+ *         <li>TermOffsets --&gt; &lt;PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock&gt;
+ *             <sup>PackedPayBlockNum</sup>
+ *         <li>PackedPayLengthBlock, PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock --&gt;
+ *             {@link PackedInts PackedInts}
+ *         <li>SumPayLength --&gt; {@link DataOutput#writeVInt VInt}
+ *         <li>PayData --&gt; {@link DataOutput#writeByte byte}<sup>SumPayLength</sup>
+ *         <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
+ *       </ul>
+ *       <p>Notes:
+ *       <ul>
+ *         <li>The order of TermPayloads/TermOffsets will be the same as TermPositions, note that
+ *             part of payload/offsets are stored in .pos.
+ *         <li>The procedure how PackedPayLengthBlock and PackedOffsetLengthBlock are generated is
+ *             the same as PackedFreqBlock in chapter <a href="#Frequencies">Frequencies and Skip
+ *             Data</a>. While PackedStartDeltaBlock follows a same procedure as
+ *             PackedDocDeltaBlock.
+ *         <li>PackedPayBlockNum is always equal to PackedPosBlockNum, for the same term. It is also
+ *             synonym for PackedOffsetBlockNum.
+ *         <li>SumPayLength is the total length of payloads written within one block, should be the
+ *             sum of PayLengths in one packed block.
+ *         <li>PayLength in PackedPayLengthBlock is the length of each payload associated with the
+ *             current position.
+ *       </ul>
+ * </dl>
+ *
+ * @lucene.experimental
+ */
+public final class Lucene99PostingsFormat extends PostingsFormat {
+
+  /**
+   * Filename extension for document number, frequencies, and skip data. See chapter: <a
+   * href="#Frequencies">Frequencies and Skip Data</a>
+   */
+  public static final String DOC_EXTENSION = "doc";
+
+  /** Filename extension for positions. See chapter: <a href="#Positions">Positions</a> */
+  public static final String POS_EXTENSION = "pos";
+
+  /**
+   * Filename extension for payloads and offsets. See chapter: <a href="#Payloads">Payloads and
+   * Offsets</a>
+   */
+  public static final String PAY_EXTENSION = "pay";
+
+  /** Size of blocks. */
+  public static final int BLOCK_SIZE = ForUtil.BLOCK_SIZE;
+
+  /**
+   * Expert: The maximum number of skip levels. Smaller values result in slightly smaller indexes,
+   * but slower skipping in big posting lists.
+   */
+  static final int MAX_SKIP_LEVELS = 10;
+
+  static final String TERMS_CODEC = "Lucene90PostingsWriterTerms";
+  static final String DOC_CODEC = "Lucene90PostingsWriterDoc";
+  static final String POS_CODEC = "Lucene90PostingsWriterPos";
+  static final String PAY_CODEC = "Lucene90PostingsWriterPay";

Review Comment:
   ```suggestion
     static final String PAY_CODEC = "Lucene99PostingsWriterPay";
   ```



-- 
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

To unsubscribe, e-mail: issues-unsubscribe@lucene.apache.org

For queries about this service, please contact Infrastructure at:
users@infra.apache.org


---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscribe@lucene.apache.org
For additional commands, e-mail: issues-help@lucene.apache.org