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HBASE-3785 book.xml - moving WAL into architecture section, plus adding more description on what it does 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1092545 13f79535-47bb-0310-9956-ffa450edef68
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Michael Stack 2011-04-14 23:06:20 +00:00
parent 0f4835a0b6
commit 8e9918a88a
2 changed files with 33 additions and 30 deletions
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2
CHANGES.txt
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@ -163,6 +163,8 @@ Release 0.91.0 - Unreleased
HBASE-3753 Book.xml - architecture, adding more Store info (Doug Meil)
HBASE-3784 book.xml - adding small subsection in architecture/client on
filters (Doug Meil)
HBASE-3785 book.xml - moving WAL into architecture section, plus adding
more description on what it does (Doug Meil)
TASKS
HBASE-3559 Move report of split to master OFF the heartbeat channel

61
src/docbkx/book.xml
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@ -878,40 +878,40 @@ HTable table2 = new HTable(conf2, "myTable");</programlisting>
</section>
</section>
</chapter>
<chapter xml:id="wal">
<title >The WAL</title>
</section>
<section xml:id="wal">
<title >Write Ahead Log (WAL)</title>
<subtitle>HBase's<link
xlink:href="http://en.wikipedia.org/wiki/Write-ahead_logging"> Write-Ahead
Log</link></subtitle>
<section xml:id="purpose.wal">
<title>Purpose</title>
<para>Each RegionServer adds updates to its Write-ahead Log (WAL)
first, and then to memory.</para>
<para>Each RegionServer adds updates (Puts, Deletes) to its write-ahead log (WAL)
first, and then to the <link linkend="store.memstore">MemStore</link> for the affected <link linkend="store">Store</link>.
This ensures that HBase has durable writes. Without WAL, there is the possibility of data loss in the case of a RegionServer failure
before each MemStore is flushed and new StoreFiles are written. <link xlink:href="http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/regionserver/wal/HLog.html">HLog</link>
is the HBase WAL implementation, and there is one HLog instance per RegionServer.
</para>The WAL is in HDFS in <filename>/hbase/.logs/</filename> with subdirectories per region.
<para>
For more general information about the concept of write ahead logs, see the Wikipedia
<link xlink:href="http://en.wikipedia.org/wiki/Write-ahead_logging">Write-Ahead Log</link> article.
</para>
</section>
<section xml:id="wal_flush">
<title>WAL Flushing</title>
<para>TODO (describe).
</para>
</section>
<section xml:id="purpose.wal">
<title>What is the purpose of the HBase WAL</title>
<section xml:id="wal_splitting">
<title>WAL Splitting</title>
<para>
See the Wikipedia
<link xlink:href="http://en.wikipedia.org/wiki/Write-ahead_logging">Write-Ahead
Log</link> article.
</para>
</section>
<section xml:id="wal_splitting">
<title>WAL splitting</title>
<subtitle>How edits are recovered from a crashed RegionServer</subtitle>
<para>When a RegionServer crashes, it will lose its ephemeral lease in
ZooKeeper...TODO</para>
<section>
<title><varname>hbase.hlog.split.skip.errors</varname></title>
<section><title>How edits are recovered from a crashed RegionServer</title>
<para>When a RegionServer crashes, it will lose its ephemeral lease in
ZooKeeper...TODO</para>
</section>
<section>
<title><varname>hbase.hlog.split.skip.errors</varname></title>
<para>When set to <constant>true</constant>, the default, any error
encountered splitting will be logged, the problematic WAL will be
@ -944,8 +944,9 @@ HTable table2 = new HTable(conf2, "myTable");</programlisting>
</section>
</section>
</section>
</chapter>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="performance.xml" />
<chapter xml:id="blooms">