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https://issues.apache.org/jira/browse/HBASE-17924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16018986#comment-16018986
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Andrew Purtell commented on HBASE-17924:
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We acquire row locks in order. Sorting the row order first means we find
conflicts faster (the first common row in sort order). The performance gain may
be hard to determine but there is also a semantics improvement. No matter what
clients are doing row lock acquisition will be in a well known order. This
latter point was our motivation over in the Phoenix project for suggesting this
change.
> 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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