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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12790) Support fairness across parallelized scans
Date Thu, 05 Nov 2015 06:36:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14991231#comment-14991231

stack commented on HBASE-12790:

bq. We will extend the groupid concept to all the client requests. That includes scan, gets,
MutateRequest, MultiRequest, Bulkloadrequest etc.

Sorry. Wasn't party to the conversation, but this seems at first blush (until I hear more),
like the wrong direction completely. Rather than making Scan "staccato", a notion that I think
you could argue should be the default behavior when scanning (its already sortof 'staccato'
given its going to be preading from hdfs), instead, the codebase is to be littered with this
arbitrary 'groupid' doohickey thingy that, truth be told, is a phoenix thing (yeah, others
could use it but its so exotic, only phoenix will be able to make sense of it).

bq. This will allow every Put, Delete, Increment, Append, Get and Scan to have a grouping

Stinks!! (Not  directed at you [~ram_krish] but whoever all who came up w/ this notion sir).

Why we need groupid at all? Scan already has an identifier kept in lease accounting, etc.
If you want grouping, arbitrate by Connection. If Connection to coarse for a client, have
your client create a new Connection per its notion of 'group', whatever that is.

A roundrobin scheduler that lives in phoenix only and that requires a rolling restart and
dedication of the cluster to phoenix-only workloads is one way to solve this, yeah, but it
seems like you have a generic problem and a generic soln would be less work and generally

> 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.

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