hbase-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12790) Support fairness across parallelized scans
Date Mon, 09 Nov 2015 19:44:11 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14997232#comment-14997232
] 

stack commented on HBASE-12790:
-------------------------------

Thanks for the eloquence [~apurtell] summarizing where we are at and how we got here using
illustration from our community past. I also appreciate and agree with your outline of the
positions involved and for hitting the reset button (should have been done long ago). 

When we reset, can the discussion be more grounded?

For example, "Opening a new HConnection takes three seconds..." I just measured it against
a cluster. Total connection setup takes 20ms... less if I let the JVM warm up. Its 3.5 seconds
to start a cold JVM, hit about 40 regions, then completely shut all down again. Improving
Connection setup is an issue many could benefit from so would be worth doing in general. We
can work on sharing cache/zk over Connections too.

Or, "It's not feasible to pool enough HConnections to support the concurrency we see over
the various types of queries."... Please substantiate your claim with numbers and use case.





> 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)

Mime
View raw message