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https://issues.apache.org/jira/browse/HBASE-5778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13531371#comment-13531371
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stack commented on HBASE-5778:
------------------------------
On commit fix this comment:
"+ * Get a reader for the WAL. If you are reading from a file that's being
written to
+ * and need to reopen it multiple times, use {@link HLog.Reader#reset()}
instead of this method
+ * then just seek back to the last known good position."
It has too much about the implementation...
This comment on reset is good... maybe use some of it:
+ // Resetting the reader lets us see newly added data if the file is being
written to
+ // We also keep the same compressionContext which was previously populated
for this file
Or the stuff in openReader is good.... too... makes sense
+1 on commit
> Turn on WAL compression by default
> ----------------------------------
>
> Key: HBASE-5778
> URL: https://issues.apache.org/jira/browse/HBASE-5778
> Project: HBase
> Issue Type: Improvement
> Reporter: Jean-Daniel Cryans
> Assignee: Jean-Daniel Cryans
> Priority: Blocker
> Fix For: 0.96.0
>
> Attachments: 5778.addendum, 5778-addendum.txt, HBASE-5778-0.94.patch,
> HBASE-5778-0.94-v2.patch, HBASE-5778-0.94-v3.patch, HBASE-5778-0.94-v4.patch,
> HBASE-5778-0.94-v5.patch, HBASE-5778.patch
>
>
> I ran some tests to verify if WAL compression should be turned on by default.
> For a use case where it's not very useful (values two order of magnitude
> bigger than the keys), the insert time wasn't different and the CPU usage 15%
> higher (150% CPU usage VS 130% when not compressing the WAL).
> When values are smaller than the keys, I saw a 38% improvement for the insert
> run time and CPU usage was 33% higher (600% CPU usage VS 450%). I'm not sure
> WAL compression accounts for all the additional CPU usage, it might just be
> that we're able to insert faster and we spend more time in the MemStore per
> second (because our MemStores are bad when they contain tens of thousands of
> values).
> Those are two extremes, but it shows that for the price of some CPU we can
> save a lot. My machines have 2 quads with HT, so I still had a lot of idle
> CPUs.
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