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https://issues.apache.org/jira/browse/HBASE-14383?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14876130#comment-14876130
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Vladimir Rodionov commented on HBASE-14383:
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{quote}
Hmm, does this policy mean that we may end up not flushing data even with
periodic flusher? The periodic flusher should be like a force flush to be
affective.
{quote}
For small stores flush happens only if they have data which is older than
periodic flush interval. This is how it works today. In theory, if you have
small heap and large number of regions you won't be able to load data fast w/o
being totally blocked periodically. ALl memstores < 16MB and they will be
flushed once an hour.
> Compaction improvements
> -----------------------
>
> Key: HBASE-14383
> URL: https://issues.apache.org/jira/browse/HBASE-14383
> Project: HBase
> Issue Type: Improvement
> Reporter: Vladimir Rodionov
> Assignee: Vladimir Rodionov
> Fix For: 2.0.0
>
>
> Still major issue in many production environments. The general recommendation
> - disabling region splitting and major compactions to reduce unpredictable
> IO/CPU spikes, especially during peak times and running them manually during
> off peak times. Still do not resolve the issues completely.
> h3. Flush storms
> * rolling WAL events across cluster can be highly correlated, hence flushing
> memstores, hence triggering minor compactions, that can be promoted to major
> ones. These events are highly correlated in time if there is a balanced
> write-load on the regions in a table.
> * the same is true for memstore flushing due to periodic memstore flusher
> operation.
> Both above may produce *flush storms* which are as bad as *compaction
> storms*.
> What can be done here. We can spread these events over time by randomizing
> (with jitter) several config options:
> # hbase.regionserver.optionalcacheflushinterval
> # hbase.regionserver.flush.per.changes
> # hbase.regionserver.maxlogs
> h3. ExploringCompactionPolicy max compaction size
> One more optimization can be added to ExploringCompactionPolicy. To limit
> size of a compaction there is a config parameter one could use
> hbase.hstore.compaction.max.size. It would be nice to have two separate
> limits: for peak and off peak hours.
> h3. ExploringCompactionPolicy selection evaluation algorithm
> Too simple? Selection with more files always wins, selection of smaller size
> wins if number of files is the same.
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