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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13408) HBase In-Memory Memstore Compaction
Date Tue, 24 Nov 2015 20:51:11 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13408?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15025366#comment-15025366
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stack commented on HBASE-13408:
-------------------------------

[~eshcar] Thanks. I missed that. There is at least one case where there is a clear benefit
(I can help w/ the latency spike). Hopefully we can have it so this feature is near always
beneficial and if not that, that it is an enabler of other features that will show general
benefit (We are on that path I believe).

> HBase In-Memory Memstore Compaction
> -----------------------------------
>
>                 Key: HBASE-13408
>                 URL: https://issues.apache.org/jira/browse/HBASE-13408
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: Eshcar Hillel
>            Assignee: Eshcar Hillel
>             Fix For: 2.0.0
>
>         Attachments: HBASE-13408-trunk-v01.patch, HBASE-13408-trunk-v02.patch, HBASE-13408-trunk-v03.patch,
HBASE-13408-trunk-v04.patch, HBASE-13408-trunk-v05.patch, HBASE-13408-trunk-v06.patch, HBASE-13408-trunk-v07.patch,
HBASE-13408-trunk-v08.patch, HBASE-13408-trunk-v09.patch, HBASE-13408-trunk-v10.patch, HBaseIn-MemoryMemstoreCompactionDesignDocument-ver02.pdf,
HBaseIn-MemoryMemstoreCompactionDesignDocument-ver03.pdf, HBaseIn-MemoryMemstoreCompactionDesignDocument-ver04.pdf,
HBaseIn-MemoryMemstoreCompactionDesignDocument.pdf, InMemoryMemstoreCompactionEvaluationResults.pdf,
InMemoryMemstoreCompactionMasterEvaluationResults.pdf, InMemoryMemstoreCompactionScansEvaluationResults.pdf,
StoreSegmentandStoreSegmentScannerClassHierarchies.pdf
>
>
> A store unit holds a column family in a region, where the memstore is its in-memory component.
The memstore absorbs all updates to the store; from time to time these updates are flushed
to a file on disk, where they are compacted. Unlike disk components, the memstore is not compacted
until it is written to the filesystem and optionally to block-cache. This may result in underutilization
of the memory due to duplicate entries per row, for example, when hot data is continuously
updated. 
> Generally, the faster the data is accumulated in memory, more flushes are triggered,
the data sinks to disk more frequently, slowing down retrieval of data, even if very recent.
> In high-churn workloads, compacting the memstore can help maintain the data in memory,
and thereby speed up data retrieval. 
> We suggest a new compacted memstore with the following principles:
> 1.	The data is kept in memory for as long as possible
> 2.	Memstore data is either compacted or in process of being compacted 
> 3.	Allow a panic mode, which may interrupt an in-progress compaction and force a flush
of part of the memstore.
> We suggest applying this optimization only to in-memory column families.
> A design document is attached.
> This feature was previously discussed in HBASE-5311.



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