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HBASE-11681 Update and move doc about disabling the WAL (Misty Stanley-Jones)

This commit is contained in:
Jonathan M Hsieh 2014-08-06 14:20:43 -07:00
parent 25e6baee42
commit 4ab6971395
2 changed files with 25 additions and 9 deletions
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15
src/main/docbkx/book.xml
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@ -2671,6 +2671,21 @@ ctime = Sat Jun 23 11:13:40 PDT 2012
</section>
</section>
</section>
<section xml:id="wal.disable">
<title>Disabling the WAL</title>
<para>It is possible to disable the WAL, to improve performace in certain specific
situations. However, disabling the WAL puts your data at risk. The only situation where
this is recommended is during a bulk load. This is because, in the event of a problem,
the bulk load can be re-run with no risk of data loss.</para>
<para>The WAL is disabled by calling the HBase client field
<code>Mutation.writeToWAL(false)</code>. Use the
<code>Mutation.setDurability(Durability.SKIP_WAL)</code> and Mutation.getDurability()
methods to set and get the field's value. There is no way to disable the WAL for only a
specific table.</para>
<warning>
<para>If you disable the WAL for anything other than bulk loads, your data is at
risk.</para></warning>
</section>
</section>
</section> <!-- regionserver -->

19
src/main/docbkx/performance.xml
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@ -564,16 +564,17 @@ admin.createTable(table, splits);
<section
xml:id="perf.hbase.client.putwal">
<title>HBase Client: Turn off WAL on Puts</title>
<para>A frequently discussed option for increasing throughput on <classname>Put</classname>s
is to call <code>writeToWAL(false)</code>. Turning this off means that the RegionServer will
<emphasis>not</emphasis> write the <classname>Put</classname> to the Write Ahead Log, only
into the memstore, HOWEVER the consequence is that if there is a RegionServer failure
<emphasis>there will be data loss</emphasis>. If <code>writeToWAL(false)</code> is used,
do so with extreme caution. You may find in actuality that it makes little difference if
your load is well distributed across the cluster. </para>
<para>A frequent request is to disable the WAL to increase performance of Puts. This is only
appropriate for bulk loads, as it puts your data at risk by removing the protection of the
WAL in the event of a region server crash. Bulk loads can be re-run in the event of a crash,
with little risk of data loss.</para>
<warning>
<para>If you disable the WAL for anything other than bulk loads, your data is at
risk.</para></warning>
<para>In general, it is best to use WAL for Puts, and where loading throughput is a concern to
use <link
linkend="perf.batch.loading">bulk loading</link> techniques instead. </para>
use <link linkend="perf.batch.loading">bulk loading</link> techniques instead. For normal
Puts, you are not likely to see a performance improvement which would outweigh the risk. To
disable the WAL, see <xref linkend="wal.disable"/>.</para>
</section>
<section
xml:id="perf.hbase.client.regiongroup">