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From "Nicolas Liochon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9873) Some improvements in hlog and hlog split
Date Wed, 06 Nov 2013 12:18:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9873?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13814843#comment-13814843

Nicolas Liochon commented on HBASE-9873:

bq. Yes, this config does help. But I think small optionalcacheflushinterval will bring small
hfiles, which sacrifices read latency and brings more compacts
Well, if the writes are "very little and periodical", it should not be an issue, no?. If we're
speaking about table heavily written, the regions should be flushed by the standard flush.

bq. Great. I can help to test and review it if needed.
Thanks a lot, I will send you the patch when it's ready.

> Some improvements in hlog and hlog split
> ----------------------------------------
>                 Key: HBASE-9873
>                 URL: https://issues.apache.org/jira/browse/HBASE-9873
>             Project: HBase
>          Issue Type: Improvement
>          Components: MTTR, wal
>            Reporter: Liu Shaohui
>            Priority: Critical
>              Labels: failover, hlog
> Some improvements in hlog and hlog split
> 1) Try to clean old hlog after each memstore flush to avoid unnecessary hlogs split in
failover.  Now hlogs cleaning only be run in rolling hlog writer. 
> 2) Add a background hlog compaction thread to compaction the hlog: remove the hlog entries
whose data have been flushed to hfile. The scenario is that in a share cluster, write requests
of a table may very little and periodical,  a lots of hlogs can not be cleaned for entries
of this table in those hlogs.
> 3) Rely on the smallest of all biggest hfile's seqId of previous served regions to ignore
some entries.  Facebook have implemented this in HBASE-6508 and we backport it to hbase 0.94
in HBASE-9568.
> 4) Support running multiple hlog splitters on a single RS and on master(latter can boost
split efficiency for tiny cluster)
> 5) Enable multiple splitters on 'big' hlog file by splitting(logically) hlog to slices(configurable
size, eg hdfs trunk size 64M)
> support concurrent multiple split tasks on a single hlog file slice 
> 6) Do not cancel the timeout split task until one task reports it succeeds (avoids scenario
where split for a hlog file fails due to no one task can succeed within the timeout period
), and and reschedule a same split task to reduce split time ( to avoid some straggler in
hlog split)
> 7) Consider the hlog data locality when schedule the hlog split task.  Schedule the hlog
to a splitter which is near to hlog data.
> 8) Support multi hlog writers and switching to another hlog writer when long write latency
to current hlog due to possible temporary network spike? 
> This is a draft which lists the improvements about hlog we try to implement in the near
future. Comments and discussions are welcomed.

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