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https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14381446#comment-14381446
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ramkrishna.s.vasudevan commented on HBASE-12790:
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bq.So is 'grouping' a pure phoenix construct or is 'grouping' just a client
identifier?
I would say it is a client identifier. It may not be phoenix specific.
bq.Or does a single phoenix client run multiple groups?
Single phoenix client - I am not getting your point here. When you say client
you mean every Phoenix client will generate a fixed group Id?
Every query can be split into parallel scans. And each query can set a unique
Scan Id. I think Phoenix does it with a random ID. (Correct me if am wrong here
[~giacomotaylor].)
bq.I ask because this scheduling of rpc in the server is a hot spot when I
profile
We could do a profile to say how much it is. I think the Phoenix team would
already have some profiling information on this area.
> Support fairness across parallelized scans
> ------------------------------------------
>
> Key: HBASE-12790
> URL: https://issues.apache.org/jira/browse/HBASE-12790
> Project: HBase
> Issue Type: New Feature
> Reporter: James Taylor
> Assignee: ramkrishna.s.vasudevan
> Labels: Phoenix
> Attachments: AbstractRoundRobinQueue.java, HBASE-12790.patch,
> HBASE-12790_1.patch
>
>
> Some HBase clients parallelize the execution of a scan to reduce latency in
> getting back results. This can lead to starvation with a loaded cluster and
> interleaved scans, since the RPC queue will be ordered and processed on a
> FIFO basis. For example, if there are two clients, A & B that submit largish
> scans at the same time. Say each scan is broken down into 100 scans by the
> client (broken down into equal depth chunks along the row key), and the 100
> scans of client A are queued first, followed immediately by the 100 scans of
> client B. In this case, client B will be starved out of getting any results
> back until the scans for client A complete.
> One solution to this is to use the attached AbstractRoundRobinQueue instead
> of the standard FIFO queue. The queue to be used could be (maybe it already
> is) configurable based on a new config parameter. Using this queue would
> require the client to have the same identifier for all of the 100 parallel
> scans that represent a single logical scan from the clients point of view.
> With this information, the round robin queue would pick off a task from the
> queue in a round robin fashion (instead of a strictly FIFO manner) to prevent
> starvation over interleaved parallelized scans.
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