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From "Chance Li (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-20312) CCSMap: A faster, GC-friendly, less memory Concurrent Map for memstore
Date Tue, 17 Apr 2018 14:17:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-20312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16440902#comment-16440902

Chance Li commented on HBASE-20312:

HBASE-20312-master.v5.patch fix a bug in close method.

> CCSMap: A faster, GC-friendly, less memory Concurrent Map for memstore
> ----------------------------------------------------------------------
>                 Key: HBASE-20312
>                 URL: https://issues.apache.org/jira/browse/HBASE-20312
>             Project: HBase
>          Issue Type: New Feature
>          Components: regionserver
>            Reporter: Xiang Wang
>            Assignee: Chance Li
>            Priority: Major
>             Fix For: 3.0.0
>         Attachments: 1.1.2-ccsmap-number.png, HBASE-20312-1.3.2.patch, HBASE-20312-master.v1.patch,
HBASE-20312-master.v2.patch, HBASE-20312-master.v3.patch, HBASE-20312-master.v4.patch, HBASE-20312-master.v5.patch,
ccsmap-branch-1.1.patch, hits.png, jira1.png, jira2.png, jira3.png, off-heap-test-put-master.png,
> Now hbase use ConcurrentSkipListMap as memstore's data structure.
> Although MemSLAB reduces memory fragment brought by key-value pairs.
> Hundred of millions key-value pairs still make young generation garbage-collection(gc)
stop time long.
> These are 2 gc problems of ConcurrentSkipListMap:
> 1. HBase needs 3 objects to store one key-value on expectation. One Index(skiplist's
average node height is 1), one Node, and one KeyValue. Too many objects are created for memstore.
> 2. Recent inserted KeyValue and its map structure(Index, Node) are assigned on young
generation.The card table (for CMS gc algorithm) or RSet(for G1 gc algorithm) will change
frequently on high writing throughput, which makes YGC slow.
> We devleoped a new skip-list map called CompactdConcurrentSkipListMap(CCSMap for short),
> which provides similary features like ConcurrentSkipListMap but get rid of Objects for
every key-value pairs.
> CCSMap's memory structure is like this picture:
> !jira1.png!
> One CCSMap consists of a certain number of Chunks. One Chunk consists of a certain number
of nodes. One node is corresspding one element. This element's all information and its key-value
is encoded on a continuous memory segment without any objects.
> Features:
> 1. all insert,update,delete operations is lock-free on CCSMap.
> 2. Consume less memory, it brings 40% memory saving for 50Byte key-value.
> 3. Faster on small key-value because of better cacheline usage. 20~30% better read/write
troughput than ConcurrentSkipListMap for 50Byte key-value.
> CCSMap do not support recyle space when deleting element. But it doesn't matter for hbase
because of region flush.
> CCSMap has been running on Alibaba's hbase clusters over 17 months, it cuts down YGC
time significantly. here are 2 graph of before and after.
> !jira2.png!
> !jira3.png!

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