Chance Li updated HBASE-20312:
    Attachment: HBASE-20312-master.v4.patch

> 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, 
> ccsmap-branch-1.1.patch, hits.png, jira1.png, jira2.png, jira3.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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