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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14918) In-Memory MemStore Flush and Compaction
Date Thu, 28 Jan 2016 13:20:39 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15121402#comment-15121402
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Anoop Sam John commented on HBASE-14918:
----------------------------------------

Ya I said it already, with the new Memstore impls it might be really possible for the move.
 My only point was that the copy to MSLAB is not a memstore impl thing at all..Or else it
has to be a duty of all of the memstore impls.   And I strongly think that for the new memstore
impl, this movement may be problematic. (I mean the flush to cellblock one).   Once the flush
to cellblock area happens, we dont need this allocator and can have a new one. (It is like
normal flush)..   And this in memory flush happens within memstore impl.. So we might not
be able to handle these if allocator is moved out..     That patch I attached just for ref.

Commit of task-1 has nothing to do with this movement.

> In-Memory MemStore Flush and Compaction
> ---------------------------------------
>
>                 Key: HBASE-14918
>                 URL: https://issues.apache.org/jira/browse/HBASE-14918
>             Project: HBase
>          Issue Type: Umbrella
>    Affects Versions: 2.0.0
>            Reporter: Eshcar Hillel
>            Assignee: Eshcar Hillel
>             Fix For: 0.98.18
>
>         Attachments: CellBlocksSegmentDesign.pdf, MSLABMove.patch
>
>
> A memstore serves as the in-memory component of a store unit, absorbing all updates to
the store. From time to time these updates are flushed to a file on disk, where they are compacted
(by eliminating redundancies) and compressed (i.e., written in a compressed format to reduce
their storage size).
> We aim to speed up data access, and therefore suggest to apply in-memory memstore flush.
That is to flush the active in-memory segment into an intermediate buffer where it can be
accessed by the application. Data in the buffer is subject to compaction and can be stored
in any format that allows it to take up smaller space in RAM. The less space the buffer consumes
the longer it can reside in memory before data is flushed to disk, resulting in better performance.
> Specifically, the optimization is beneficial for workloads with medium-to-high key churn
which incur many redundant cells, like persistent messaging. 
> We suggest to structure the solution as 4 subtasks (respectively, patches). 
> (1) Infrastructure - refactoring of the MemStore hierarchy, introducing segment (StoreSegment)
as first-class citizen, and decoupling memstore scanner from the memstore implementation;
> (2) Adding StoreServices facility at the region level to allow memstores update region
counters and access region level synchronization mechanism;
> (3) Implementation of a new memstore (CompactingMemstore) with non-optimized immutable
segment representation, and 
> (4) Memory optimization including compressed format representation and off heap allocations.
> This Jira continues the discussion in HBASE-13408.
> Design documents, evaluation results and previous patches can be found in HBASE-13408.




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