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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9467) write can be totally blocked temporarily by a write-heavy region
Date Tue, 10 Sep 2013 23:31:52 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9467?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13763699#comment-13763699
] 

Todd Lipcon commented on HBASE-9467:
------------------------------------

Sorry, hit submit too quickly... I meant to add that this approach is much better because
it also helps with the problem of multiple different priority clients hitting the same region
-- for example, a low priority MR job doing bulk puts into a region at the same time as a
latency sensitive web app is doing single row requests. If you could set the watermarks for
the low priority clients differently than high-priority clients, then rejecting the low priority
ones and making them retry on the client side will leave room (both handler-wise and capacity
wise) for the high priority ones to get in without sitting in lengthy RPC queues.
                
> write can be totally blocked temporarily by a write-heavy region
> ----------------------------------------------------------------
>
>                 Key: HBASE-9467
>                 URL: https://issues.apache.org/jira/browse/HBASE-9467
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Feng Honghua
>            Priority: Minor
>
> Write to a region can be blocked temporarily if the memstore of that region reaches the
threshold(hbase.hregion.memstore.block.multiplier * hbase.hregion.flush.size) until the memstore
of that region is flushed.
> For a write-heavy region, if its write requests saturates all the handler threads of
that RS when write blocking for that region occurs, requests of other regions/tables to that
RS also can't be served due to no available handler threads...until the pending writes of
that write-heavy region are served after the flush is done. Hence during this time period,
from the RS perspective it can't serve any request from any table/region just due to a single
write-heavy region.
> This sounds not very reasonable, right? Maybe write requests from a region can only be
served by a sub-set of the handler threads, and then write blocking of any single region can't
lead to the scenario mentioned above?
> Comment?

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