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From "Eric Newton (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-3423) speed up WAL roll-overs
Date Tue, 16 Dec 2014 00:33:13 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-3423?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14247495#comment-14247495
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Eric Newton commented on ACCUMULO-3423:
---------------------------------------

 # Master could also clean up old tserver log markers, but it might be safer to let the GC
do it.


> speed up WAL roll-overs
> -----------------------
>
>                 Key: ACCUMULO-3423
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-3423
>             Project: Accumulo
>          Issue Type: Bug
>          Components: master, tserver
>            Reporter: Eric Newton
>
> After reading the proposal on HBASE-10278, I realized there are many ways to make the
Accumulo WAL roll-over faster.
> # Open two WALogs, but use only one until it reaches the WALog roll-over size
> # Rollover consists only of swapping the writers
> # WALog roll consists of the final close, which can happen in parallel
> # Don't mark the tablets with log entries: they are already marked with the tserver
> # The tserver can make notes about the logs-in-use in the metadata table(s) as part of
opening the log.
> # The master can copy the log entries to tablets while unassigning them,  piggybacking
on the unassigment mutation.
> # Tablet servers can remove their current log entries from the metadata tables when they
have no tablets using them.
> There are two issues: 
> # tablets will have an empty file in recovery, nearly all the time, but the recovery
code already handles that case.  
> # presently, a tablet doesn't have a marker for a log it did not use. Many more tablets
will attempt to recover when it is unnecessary.
> This would also address ACCUMULO-2889.



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