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From "Allan Yang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17924) Consider sorting the row order when processing multi() ops before taking rowlocks
Date Sun, 21 May 2017 07:17:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16018713#comment-16018713
] 

Allan Yang commented on HBASE-17924:
------------------------------------

{quote}
Thanks for pointing me here from HBASE-18074 Allan Yang. Did you find any perf benefit sorting?

{quote}
No, we haven't run some performance data for the patch yet, I will provide some if I have
time to do so. But the patch should help with situation which parallel threads are executing
multi with disordered keys(some kyes are the same). 
{quote}
The sort costs but knowing that mutations coming in are sorted, perhaps in doMiniBatch I could
have a single lock cover all mutations on the same row that follow (but this would involve
a bunch of row compares).
{quote}
Now, row lock is a ReadWrite lock. It is a reentrantlock. I don't know which is more costing,
lock the same row or compare the rows, avoiding lock the same row twice. If locking the locked
reentrantlock is more costing than compare the rows in bytes, then I think your idea is doable。


> Consider sorting the row order when processing multi() ops before taking rowlocks
> ---------------------------------------------------------------------------------
>
>                 Key: HBASE-17924
>                 URL: https://issues.apache.org/jira/browse/HBASE-17924
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 2.0.0, 1.1.8
>            Reporter: Andrew Purtell
>            Assignee: Allan Yang
>             Fix For: 2.0.0, 1.4.0
>
>         Attachments: HBASE-17924.patch, HBASE-17924.v0.patch, HBASE-17924.v2.patch, HBASE-17924.v3.patch,
HBASE-17924.v4.patch, HBASE-17924.v5.patch
>
>
> When processing a batch mutation, we take row locks in whatever order the mutations were
added to the multi op by the client.
>  
> {noformat}
> RSRpcServices#multi -> RSRpcServices#mutateRows -> HRegion#mutateRow -> HRegion#mutateRowsWithLocks
-> HRegion#processRowsWithLocks
> {noformat}
> Or
> {noformat}
> RSRpcServices#multi -> RSRpcServices#doNonAtomicRegionMutation ->
>       HRegion#get 
>     | HRegion#append 
>     | HRegion#increment 
>     | HRegionServer#doBatchOp -> HRegion#batchMutate -> HRegion#doMiniBatchMutation
> {noformat}
>  
> multi() is fed by client APIs that accept a RowMutations object containing actions for
multiple rows. The container for ops inside RowMutations is an ArrayList, which doesn't change
the ordering of objects added to it. The protobuf implementation of the messages for multi
ops do not reorder the list of actions. When processing multi ops we iterate over the actions
in the order rehydrated from protobuf.
> We should discuss sorting the order of ops by row key when processing multi() ops before
taking row locks. Does this make lock ordering more predictable for server side operations?
Yes, but potentially surprising for the client, right? Is there any legitimate reason we should
take locks out of row key sorted order because the client has structured the request as such?



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