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https://issues.apache.org/jira/browse/HBASE-20312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16443140#comment-16443140
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Mike Drob commented on HBASE-20312:
-----------------------------------
[~chancelq] - did you see my earlier question?
bq. If CCSMap is meant to be independent of HBase and a more generic data
structure, have you considered submitting it to some project like apache
commons-collections or google guava collections and then referencing those
classes from HBase? Or even publishing it as its own project on github?
Further, there is a _lot_ of code here. Can we break this work into phases or
stages or anything like that to make it easier to understand and get some
pieces in without waiting for everything to be perfect?
> 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, HBASE-20312-master.v6.patch,
> HBASE-20312-master.v7.patch, ccsmap-branch-1.1.patch, hits.png, jira1.png,
> jira2.png, jira3.png, off-heap-test-put-master.png,
> on-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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