[
https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14994538#comment-14994538
]
stack commented on HBASE-12790:
-------------------------------
bq. Scan attributes alone will not do IMHO because the queues cannot do this
round robin for now.
They can round robin over the Scans but you are saying the scheduler needs to
distinguish at a higher level than per Scan? It can't arbitrate on Scanner
lease or a Scanner id attribute? Scheduler needs to make sure that we schedule
scans from different clients... We could just schedule the same client over and
over and shut out all others?
bq. Let me check that more closely in terms of phoenix code also.
Thanks.
bq. ...or provide a scheduler that does.
I agree with this bit. Long scans or a single client hogging server resources
is broke for everyone. Lets fix it for all rather than just for phoenix?
bq. ....how about we do the simple suggestion that Andrew Purtell suggested to
fix up the patch to handle writes too?
Because it pulls in an alien notion of 'groups', a tiering/complication that we
can hopefully do without.
> 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, HBASE-12790_5.patch, HBASE-12790_callwrapper.patch,
> HBASE-12790_trunk_1.patch, PHOENIX_4.5.3-HBase-0.98-2317-SNAPSHOT.zip
>
>
> 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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
