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Posted to issues@iceberg.apache.org by GitBox <gi...@apache.org> on 2022/06/09 22:18:35 UTC
[GitHub] [iceberg] szehon-ho commented on a diff in pull request #4944: Add Puffin, indices and stats file format specification
szehon-ho commented on code in PR #4944:
URL: https://github.com/apache/iceberg/pull/4944#discussion_r894006356
##########
format/puffin-spec.md:
##########
@@ -0,0 +1,144 @@
+---
+url: puffin-spec
+toc: false
+---
+<!--
+ - 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.
+ -->
+
+# Puffin file format
+
+This is a specification for Puffin, a file format designed to store
+information such as indexes and statistics about data managed in an
+Iceberg table that cannot be stored directly within the Iceberg manifest. A
+Puffin file contains arbitrary pieces of information (here called "blobs"),
+along with metadata necessary to interpret them. The blobs supported by Iceberg
+are documented at [Blob types](#blob-types).
+
+## Format specification
+
+A file conforming to the Puffin file format specification should have the structure
+as described below.
+
+### Versions
+
+Currently, there is a single version of the Puffin file format, described below.
+
+### File structure
+
+The Puffin file has the following structure
+
+```
+Magic Blob₁ Blob₂ ... Blobₙ Footer
+```
+
+where
+
+- `Magic` is four bytes 0x50, 0x46, 0x41, 0x31 (short for: Puffin _Fratercula
+ arctica_, version 1),
+- `Blobᵢ` is i-th blob contained in the file, to be interpreted by application
+ according to the footer,
+- `Footer` is defined below.
+
+### Footer structure
+
+Footer has the following structure
+
+```
+Magic FooterPayload FooterPayloadSize Flags Magic
+```
+
+where
+
+- `Magic`: four bytes, same as at the beginning of the file
+- `FooterPayload`: optionally compressed, UTF-8 encoded JSON payload describing the
+ blobs in the file, with the structure described below
+- `FooterPayloadSize`: a length in bytes of the `FooterPayload` (after compression,
+ if compressed), stored as 4 byte integer
+- `Flags`: 4 bytes for boolean flags
+ - byte 0 (first)
+ - bit 0 (lowest bit): whether `FooterPayload` is compressed
+ - all other bits are reserved for future use and should be set to 0 on write
+ - all other bytes are reserved for future use and should be set to 0 on write
+
+A 4 byte integer is always signed, in a two's complement representation, stored
+little-endian.
+
+### Footer Payload
+
+Footer payload bytes is either uncompressed or LZ4-compressed (as a single
+[LZ4 compression frame](https://github.com/lz4/lz4/blob/77d1b93f72628af7bbde0243b4bba9205c3138d9/doc/lz4_Frame_format.md)
+with content size present), UTF-8 encoded JSON payload representing a single
+`FileMetadata` object.
+
+#### FileMetadata
+
+`FileMetadata` has the following fields
+
+
+| Field Name | Field Type | Required | Description |
+| ---------- | --------------------------------------- | -------- | ----------- |
+| blobs | list of BlobMetadata objects | yes |
+| properties | JSON object with string property values | no | storage for arbitrary meta-information, like writer identification/version. See [Common properties](#common-properties) for properties that are recommended to be set by a writer.
+
+#### BlobMetadata
+
+`BlobMetadata` has the following fields
+
+| Field Name | Field Type | Required | Description |
+|-------------------|-----------------------------------------|----------| ----------- |
+| type | JSON string | yes | See [Blob types](#blob-types)
+| fields | list of JSON long | yes | List of field IDs the blob was computed for; the order of items is used to compute sketches stored in the blob.
+| offset | JSON long | yes | The offset in the file where the blob contents start
+| length | JSON long | yes | The length of the blob stored in the file (after compression, if compressed)
+| compression-codec | JSON string | no | See [Compression codecs](#compression-codecs). If omitted, the data is assumed to be uncompressed.
+| properties | JSON object with string property values | no | storage for arbitrary meta-information about the blob
+
+### Blob types
+
+The blobs can be of a type listed below
+
+#### `apache-datasketches-theta-v1` blob type
Review Comment:
So to clarify, alpha-sketch is just one example, and the idea here is it support various statistics/secondary index that is to be defined, right? Example, other sketches, or even bloom filter?
##########
format/puffin-spec.md:
##########
@@ -0,0 +1,144 @@
+---
+url: puffin-spec
+toc: false
+---
+<!--
+ - 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.
+ -->
+
+# Puffin file format
+
+This is a specification for Puffin, a file format designed to store
+information such as indexes and statistics about data managed in an
+Iceberg table that cannot be stored directly within the Iceberg manifest. A
+Puffin file contains arbitrary pieces of information (here called "blobs"),
+along with metadata necessary to interpret them. The blobs supported by Iceberg
+are documented at [Blob types](#blob-types).
+
+## Format specification
+
+A file conforming to the Puffin file format specification should have the structure
+as described below.
+
+### Versions
+
+Currently, there is a single version of the Puffin file format, described below.
+
+### File structure
+
+The Puffin file has the following structure
+
+```
+Magic Blob₁ Blob₂ ... Blobₙ Footer
+```
+
+where
+
+- `Magic` is four bytes 0x50, 0x46, 0x41, 0x31 (short for: Puffin _Fratercula
+ arctica_, version 1),
+- `Blobᵢ` is i-th blob contained in the file, to be interpreted by application
+ according to the footer,
+- `Footer` is defined below.
+
+### Footer structure
+
+Footer has the following structure
+
+```
+Magic FooterPayload FooterPayloadSize Flags Magic
+```
+
+where
+
+- `Magic`: four bytes, same as at the beginning of the file
+- `FooterPayload`: optionally compressed, UTF-8 encoded JSON payload describing the
+ blobs in the file, with the structure described below
+- `FooterPayloadSize`: a length in bytes of the `FooterPayload` (after compression,
+ if compressed), stored as 4 byte integer
+- `Flags`: 4 bytes for boolean flags
+ - byte 0 (first)
+ - bit 0 (lowest bit): whether `FooterPayload` is compressed
+ - all other bits are reserved for future use and should be set to 0 on write
+ - all other bytes are reserved for future use and should be set to 0 on write
+
+A 4 byte integer is always signed, in a two's complement representation, stored
+little-endian.
+
+### Footer Payload
+
+Footer payload bytes is either uncompressed or LZ4-compressed (as a single
+[LZ4 compression frame](https://github.com/lz4/lz4/blob/77d1b93f72628af7bbde0243b4bba9205c3138d9/doc/lz4_Frame_format.md)
+with content size present), UTF-8 encoded JSON payload representing a single
+`FileMetadata` object.
+
+#### FileMetadata
+
+`FileMetadata` has the following fields
+
+
+| Field Name | Field Type | Required | Description |
+| ---------- | --------------------------------------- | -------- | ----------- |
+| blobs | list of BlobMetadata objects | yes |
+| properties | JSON object with string property values | no | storage for arbitrary meta-information, like writer identification/version. See [Common properties](#common-properties) for properties that are recommended to be set by a writer.
+
+#### BlobMetadata
+
+`BlobMetadata` has the following fields
+
+| Field Name | Field Type | Required | Description |
+|-------------------|-----------------------------------------|----------| ----------- |
+| type | JSON string | yes | See [Blob types](#blob-types)
+| fields | list of JSON long | yes | List of field IDs the blob was computed for; the order of items is used to compute sketches stored in the blob.
+| offset | JSON long | yes | The offset in the file where the blob contents start
+| length | JSON long | yes | The length of the blob stored in the file (after compression, if compressed)
+| compression-codec | JSON string | no | See [Compression codecs](#compression-codecs). If omitted, the data is assumed to be uncompressed.
+| properties | JSON object with string property values | no | storage for arbitrary meta-information about the blob
+
+### Blob types
+
+The blobs can be of a type listed below
+
+#### `apache-datasketches-theta-v1` blob type
Review Comment:
So to clarify, alpha-sketch is just one example, and the idea here is it support various statistics/secondary index that is to be defined, right? Example, other sketches, or even bloom filter?
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