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From "Thomas Pan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8817) Enhance The Apache HBase Reference Guide
Date Fri, 19 Jul 2013 05:52:57 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8817?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13713357#comment-13713357

Thomas Pan commented on HBASE-8817:

Memstore flush

Memstore flush can be triggered under three conditions listed below. The minimum flush unit
is per region, not at individual memstore level.

1. When a memstore reaches the value specified by hbase.hregion.memstore.flush.size, memstores
that belong to its region will be flushed out to disk.
2. When overall memstore usage reaches the value specified by hbase.regionserver.global.memstore.upperLimit,
memstores from various regions will be flushed out to disk to reduce overall memstore usage
in a Region Server. The flush order is based on the descending order of region memstore usage.
There will be enough regions with their memstore flushed out until the overall memstore usage
drops to or slightly below hbase.regionserver.global.memstore.lowerLimit.
3. When number of HLog per region server reaches the value specified in hbase.regionserver.max.logs,
memstores from various regions will be flushed out to disk to reduce HLog count. The flush
order is based on time with regions having oldest memstores got flushed first until HLog count
drops below hbase.regionserver.max.logs.

> Enhance The Apache HBase Reference Guide
> ----------------------------------------
>                 Key: HBASE-8817
>                 URL: https://issues.apache.org/jira/browse/HBASE-8817
>             Project: HBase
>          Issue Type: Bug
>          Components: documentation
>            Reporter: Thomas Pan
> I am reading the guide here: http://hbase.apache.org/book.html#regions.arch
> I have noticed the following:
> - There is lack of coverage on scan. Note that Lars has a very good presentation from
last year's HBaseCon: http://www.slideshare.net/cloudera/3-learning-h-base-internals-lars-hofhansl-salesforce-final
> - Under section, there is no mentioning of flush per region if a memstore reached
the size threshold (and a possible flush of all memstores if over all memory usage of all
the memstores reached memstore.upperlimit). Note that people need to combine the information
provided in section 9 with section to fully understand the situation.
> - Compaction tuning strategies. Both Nicolas from Facebook and Sergey from Hortonworks
have presented various compaction algorithms. Sometime, once all the necessary code is in
master, we need to have the coverage.
> Let me know how I can help on the matter.

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