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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-15716) HRegion#RegionScannerImpl scannerReadPoints synchronization costs
Date Tue, 26 Apr 2016 21:32:12 GMT

     [ https://issues.apache.org/jira/browse/HBASE-15716?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

stack updated HBASE-15716:
--------------------------
    Attachment: Screen Shot 2016-04-26 at 2.25.26 PM.png
                remove_cslm.patch

This patch removes the CSLM in favor of a HM since we don't need CSLM especially given we
are synchronizing currently... only, it doesn't help. FR still notes the synchronizes (and
throughput is same as w/ CSLM..)

So, [~lhofhansl]... do we need to synchronize in here? We lock because we want the smallest
read point... the oldest outstanding scanner. Does the lock help here? The lock will ensure
we see newer scanners.... but we don't care about newer scanners.... just the one w/ the oldest
read point. Can we just remove this synchronization and just pivot on the content of the scannerReadPoints
CSLM?

Let me put up a patch.

> HRegion#RegionScannerImpl scannerReadPoints synchronization costs
> -----------------------------------------------------------------
>
>                 Key: HBASE-15716
>                 URL: https://issues.apache.org/jira/browse/HBASE-15716
>             Project: HBase
>          Issue Type: Bug
>          Components: Performance
>            Reporter: stack
>         Attachments: Screen Shot 2016-04-26 at 2.05.45 PM.png, Screen Shot 2016-04-26
at 2.06.14 PM.png, Screen Shot 2016-04-26 at 2.07.06 PM.png, Screen Shot 2016-04-26 at 2.25.26
PM.png, remove_cslm.patch
>
>
> Here is a [~lhofhansl] special.
> When we construct the region scanner, we get our read point and then store it with the
scanner instance in a Region scoped CSLM. This is done under a synchronize on the CSLM.
> This synchronize on a region-scoped Map creating region scanners is the outstanding point
of lock contention according to flight recorder (My work load is workload c, random reads).



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