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https://issues.apache.org/jira/browse/HBASE-5311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13197581#comment-13197581
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Todd Lipcon commented on HBASE-5311:
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Another thing I've considered and mentioned to people, but don't think is
tracked on JIRA, is to do "in-memory flushes". Our memstores are
ConcurrentSkipListMaps, which have the nice property of being lock-free for
contending updates, but the poor property of having bad cache locality and
being less efficient on the read side (beware: unsubstantiated claim).
If we periodically flushed to in-memory "dense" storage, we'd probably get a
bunch of benefits:
- scans should be faster since we could order the KVs in memory according to
their sort order, in a dense array (taking advantage of sequential memory
access being much faster than random)
- reads in general should be faster since there would be less contention on the
datastructure
- we could use less memory by using a more tightly packed data structure for
the immutable data, or even using HFile compression methods there
> Allow inmemory Memstore compactions
> -----------------------------------
>
> Key: HBASE-5311
> URL: https://issues.apache.org/jira/browse/HBASE-5311
> Project: HBase
> Issue Type: Improvement
> Reporter: Lars Hofhansl
>
> Just like we periodically compact the StoreFiles we should also periodically
> compact the MemStore.
> During these compactions we eliminate deleted cells, expired cells, cells to
> removed because of version count, etc, before we even do a memstore flush.
> Besides the optimization that we could get from this, it should also allow us
> to remove the special handling of ICV, Increment, and Append (all of which
> use upsert logic to avoid accumulating excessive cells in the Memstore).
> Not targeting this.
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