[jira] [Updated] (HBASE-5074) support checksums in HBase block cache

["Phabricator (Updated) (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-5074?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Phabricator updated HBASE-5074:
-------------------------------

    Attachment: D1521.1.patch

dhruba requested code review of "[jira] [HBASE-5074] Support checksums in HBase block cache".
Reviewers: mbautin

  HFile is enhanced to store a checksum for each block. HDFS checksum verification is avoided while reading data into the block cache. On a checksum verification failure, we retry the file system read request with hdfs checksums switched on (thanks Todd).

  I have a benchmark that shows that it reduces iops on the disk by about 40%. In this experiment, the entire memory on the regionserver is allocated to the regionserver's jvm and the OS buffer cache size is negligible. I also measured  negligible (<5%) additional cpu usage while using hbase-level checksums.

  The salient points of this patch:

  1. Each hfile's trailer used to have a 4 byte version number. I enhanced this so that these 4 bytes can be interpreted as a (major version number, minor version). Pre-existing hfiles have a minor version of 0. The new hfile format has a minor version of 1 (thanks Mikhail). The hfile major version remains unchanged at 2. The reason I did not introduce a new major version number is because the code changes needed to store/read checksums do not differ much from existing V2 writers/readers.

  2. Introduced a HFileSystem object which is a encapsulates the FileSystem objects needed to access data from hfiles and hlogs.  HDFS FileSystem objects already had the ability to switch off checksum verifications for reads.

  3. The majority of the code changes are located in hbase.io.hfie package. The retry of a read on an initial checksum failure occurs inside the hbase.io.hfile package itself.  The code changes to hbase.regionserver package are minor.

  4. The format of a hfileblock is the header followed by the data followed by the checksum(s). Each 16 K (configurable) size of data has a 4 byte checksum.  The hfileblock header has two additional fields: a 4 byte value to store the bytesPerChecksum and a 4 byte value to store the size of the user data (excluding the checksum data). This is well explained in the associated javadocs.

  5. I added a test to test backward compatibility. I will be writing more unit tests that triggers checksum verification failures aggressively. I have left a few redundant log messages in the code (just for easier debugging) and will remove them in later stage of this patch. I will also be adding metrics on number of checksum verification failures/success in a later version of this diff.

  6. By default, hbase-level checksums are switched on and hdfs level checksums are switched off for hfile-reads. No changes to Hlog code path here.

TEST PLAN
  The default setting is to switch on hbase checksums for hfile-reads, thus all existing tests actually validate the new code pieces. I will be writing more unit tests for triggering checksum verification failures.

REVISION DETAIL
  https://reviews.facebook.net/D1521

AFFECTED FILES
  src/test/java/org/apache/hadoop/hbase/HBaseTestingUtility.java
  src/test/java/org/apache/hadoop/hbase/HBaseTestCase.java
  src/test/java/org/apache/hadoop/hbase/regionserver/TestSplitTransaction.java
  src/test/java/org/apache/hadoop/hbase/regionserver/wal/TestWALReplay.java
  src/test/java/org/apache/hadoop/hbase/regionserver/TestScanWithBloomError.java
  src/test/java/org/apache/hadoop/hbase/regionserver/TestCompoundBloomFilter.java
  src/test/java/org/apache/hadoop/hbase/regionserver/TestStore.java
  src/test/java/org/apache/hadoop/hbase/regionserver/TestStoreFile.java
  src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlock.java
  src/test/java/org/apache/hadoop/hbase/io/hfile/TestCacheOnWrite.java
  src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileReaderV1.java
  src/test/java/org/apache/hadoop/hbase/io/hfile/CacheTestUtils.java
  src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlockIndex.java
  src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileDataBlockEncoder.java
  src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlockCompatibility.java
  src/test/java/org/apache/hadoop/hbase/io/TestHalfStoreFileReader.java
  src/test/java/org/apache/hadoop/hbase/util/TestMergeTable.java
  src/main/java/org/apache/hadoop/hbase/HConstants.java
  src/main/java/org/apache/hadoop/hbase/util/HFileSystem.java
  src/main/java/org/apache/hadoop/hbase/util/ChecksumByteArrayOutputStream.java
  src/main/java/org/apache/hadoop/hbase/util/CompoundBloomFilter.java
  src/main/java/org/apache/hadoop/hbase/util/ChecksumFactory.java
  src/main/java/org/apache/hadoop/hbase/regionserver/handler/OpenRegionHandler.java
  src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java
  src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/HFilePrettyPrinter.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/HFileDataBlockEncoderImpl.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderV2.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/HFile.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/HFileWriterV2.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/HFileDataBlockEncoder.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/AbstractHFileReader.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/NoOpDataBlockEncoder.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/FixedFileTrailer.java
  src/main/java/org/apache/hadoop/hbase/io/hfile/HFileWriterV1.java

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> support checksums in HBase block cache
> --------------------------------------
>
>                 Key: HBASE-5074
>                 URL: https://issues.apache.org/jira/browse/HBASE-5074
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: D1521.1.patch, D1521.1.patch
>
>
> The current implementation of HDFS stores the data in one block file and the metadata(checksum) in another block file. This means that every read into the HBase block cache actually consumes two disk iops, one to the datafile and one to the checksum file. This is a major problem for scaling HBase, because HBase is usually bottlenecked on the number of random disk iops that the storage-hardware offers.

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