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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-15477) Do not save 'next block header' when we cache hfileblocks
Date Thu, 17 Mar 2016 19:48:33 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15200240#comment-15200240
] 

stack commented on HBASE-15477:
-------------------------------

Commit message. Will post to rb when I do up v2 of this patch.

{code}
When we read from HDFS, we overread to pick up the next blocks header.
Doing this saves a seek as we move through the hfile; we save having to
do an explicit seek just to read the block header every time we need to
read the body.  We used to read in the next header as part of the
current blocks buffer. This buffer was then what got persisted to
blockcache; so we were over-persisting: our block plus the next blocks'
header (33 bytes).

This patch undoes this over-persisting.

Removes support for version 1 blocks (0.2 was added in hbase-0.92.0).
Not needed any more.

There is an open question on whether checksums should be persisted
when caching. The code seems to say no but if cache is SSD backed or
backed by anything that does not do error correction, we'll want
checksums.

Adds loads of documentation.

M hbase-common/src/main/java/org/apache/hadoop/hbase/io/hfile/BlockType.java
  (write) Add writing from a ByteBuff.

M hbase-common/src/main/java/org/apache/hadoop/hbase/nio/ByteBuff.java
  (toString) Add one so ByteBuff looks like ByteBuffer when you click on
  it in IDE

M hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java
  Remove support for version 1 blocks.

  Cleaned up handling of metadata added when we serialize a block to
  caches. Metadata is smaller now.

  When we serialize (used when caching), do not persist the next blocks
  header if present.

  Removed a bunch of methods, a few of which had overlapping
  functionality and others that exposed too much of our internals.
  Also removed a bunch of constructors and unified the constructors we
  had left over making them share a common init method.
  Shutdown access to defines that should only be used internally here.

  Renamed all to do w/ 'EXTRA' and 'extraSerialization' to instead talk
  about metadata saved to caches; was unclear previously what EXTRA was
  about.

  Renamed static final declarations as all uppercase.

  (readBlockDataInternal): Redid. Couldn't make sense of it previously.
  Undid heavy-duty parse of header by constructing HFileBlock. Other
  cleanups. Its 1/3rd the length it used to be. More to do in here.

diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileScanner.java
b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileScanner.java
  Add deprecations of silly methods.

M hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java
  Do allocation-saving serialization in an less-intrusive way.
  TODO: Can we pass HFileBlock a Writer Interface so it can do
  serialization?

M hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/CacheTestUtils.java
  Don't use HFileBlock internals

M hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestChecksum.java
M hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlock.java
M hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlockIndex.java
M hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileEncryption.java
M hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileWriterV3.java
  API reading a block changed. No need to pass in version 1 compressed
  size anymore.

D hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlockCompatibility.java
  Removed. No support for version 1 anymore.
{code}

> Do not save 'next block header' when we cache hfileblocks
> ---------------------------------------------------------
>
>                 Key: HBASE-15477
>                 URL: https://issues.apache.org/jira/browse/HBASE-15477
>             Project: HBase
>          Issue Type: Sub-task
>          Components: BlockCache, Performance
>            Reporter: stack
>            Assignee: stack
>         Attachments: 15477.patch
>
>
>     When we read from HDFS, we overread to pick up the next blocks header.
>     Doing this saves a seek as we move through the hfile; we save having to
>     do an explicit seek just to read the block header every time we need to
>     read the body.  We used to read in the next header as part of the
>     current blocks buffer. This buffer was then what got persisted to
>     blockcache; so we were over-persisting wrtiting out our block plus the
>     next blocks' header (overpersisting 33 bytes). Parse of HFileBlock
>     complicated by this extra tail. Fix.



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