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From "Thomas Pan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8817) Enhance The Apache HBase Reference Guide
Date Tue, 09 Jul 2013 06:03:49 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8817?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13702960#comment-13702960
] 

Thomas Pan commented on HBASE-8817:
-----------------------------------


Let me start with the simpler one, regarding flushes. Please verify that my understanding
is correct.

2.3.1.1. HBase Default Configuration

hbase.regionserver.global.memstore.upperLimit

Maximum size of all memstores in a region server before new updates are blocked and flushes
are forced. Defaults to 40% of heap. Updates are blocked and region level flushes are forced
until size of all memstores in a region server hits hbase.regionserver.global.memstore.lowerLimit.

hbase.hregion.memstore.flush.size

Memstore will be flushed to disk if size of the memstore exceeds this number of bytes. When
that happens, memstores that belong to the same region will all be flushed. Value is checked
by a thread that runs every hbase.server.thread.wakefrequency.

9.7.6.1. MemStore
The MemStore holds in-memory modifications to the Store. Modifications are KeyValues. When
asked to flush, current memstore is moved to snapshot and is cleared. HBase continues to serve
edits out of new memstore and backing snapshot until flusher reports in that the flush succeeded.
At this point the snapshot is let go. Note that when flush happens, memstores that belong
to the same region will all be flushed out.

                
> 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 9.7.6.1, 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 2.3.1.1 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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