Author: stack
Date: Thu Apr 14 23:06:20 2011
New Revision: 1092545
URL: http://svn.apache.org/viewvc?rev=1092545&view=rev
Log:
HBASE-3785 book.xml - moving WAL into architecture section, plus adding more
description on what it does
Modified:
hbase/trunk/CHANGES.txt
hbase/trunk/src/docbkx/book.xml
Modified: hbase/trunk/CHANGES.txt
URL:
http://svn.apache.org/viewvc/hbase/trunk/CHANGES.txt?rev=1092545&r1=1092544&r2=1092545&view=diff
==============================================================================
--- hbase/trunk/CHANGES.txt (original)
+++ hbase/trunk/CHANGES.txt Thu Apr 14 23:06:20 2011
@@ -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
Modified: hbase/trunk/src/docbkx/book.xml
URL:
http://svn.apache.org/viewvc/hbase/trunk/src/docbkx/book.xml?rev=1092545&r1=1092544&r2=1092545&view=diff
==============================================================================
--- hbase/trunk/src/docbkx/book.xml (original)
+++ hbase/trunk/src/docbkx/book.xml Thu Apr 14 23:06:20 2011
@@ -878,40 +878,40 @@ HTable table2 = new HTable(conf2, "myTab
</section>
- </section>
- </chapter>
-
- <chapter xml:id="wal">
- <title >The WAL</title>
-
- <subtitle>HBase's<link
- xlink:href="http://en.wikipedia.org/wiki/Write-ahead_logging";> Write-Ahead
- Log</link></subtitle>
-
- <para>Each RegionServer adds updates to its Write-ahead Log (WAL)
- first, and then to memory.</para>
-
- <section xml:id="purpose.wal">
- <title>What is the purpose of the HBase WAL</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>
+ </section>
+ <section xml:id="wal">
+ <title >Write Ahead Log (WAL)</title>
+
+ <section xml:id="purpose.wal">
+ <title>Purpose</title>
+
+ <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>
- <subtitle>How edits are recovered from a crashed RegionServer</subtitle>
+ <section xml:id="wal_splitting">
+ <title>WAL Splitting</title>
- <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, "myTab
</section>
</section>
+ </section>
</chapter>
-
+
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude";
href="performance.xml" />
<chapter xml:id="blooms">
