[
https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14995953#comment-14995953
]
stack commented on HBASE-12790:
-------------------------------
bq. What's the resistance to having a round robin scheduler?
None. See above where I argue this should probably be made the default. The
discussion is about what to round robin over. Please answer the question asked
(allow that there is a ConnectionPool as there is for other DBs so no
setup-time in-line).
Your Maptask illustration doesn't help your case given each Mapper will put up
its own Connection (it is an argument in favor of scheduling across
Connections).
bq. What's the reason to not have this optionally configurable, round-robin
scheduler?
The argument has been made a few times above (i.e. introduces a new
tier/complexity/friction on scheduler when it doesn't seem like we need it,
when it looks like we can do a more simple approach that would work inherently
without apps having to ask for the behavior... etc.)
> 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)
