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https://issues.apache.org/jira/browse/HBASE-2468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12870321#action_12870321
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stack commented on HBASE-2468:
------------------------------
I'm for default behavior being grabbing more than just the one row -- ten or
something. Regards full-table scan as default, I think it should be an option
(Its a nice option to have).
On code, here's some comments (Congrats Mingjie on first submission):
Change
{code}
+ this.preFetchRegionLimit = 10;
{code}
.. to be
{code}
+ this.preFetchRegionLimit = conf.getInt("hbase.client.prefetch.limit",
10);
{code}
IMO, never hardcode things like this, and IMO, you don't need to put the config
out in the hbse-default.xml.... just do the above. Someone who really needs to
change it can read code and figure its possible. If it becomes a popular
change people make, then we can move it out to hbase-default.xml.
Regards methods that you only call from a unit test, should they be package
protected rather than protected; i.e. narrower access than protected?
Nit. You don't need to explain in unit test javadoc why the fix: e.g.:
{code}
+ * This fix is provided to prevent potential storm of META reads for a
+ * very large table.
{code}
Otherwise, patch looks great.
> Improvements to prewarm META cache on clients
> ---------------------------------------------
>
> Key: HBASE-2468
> URL: https://issues.apache.org/jira/browse/HBASE-2468
> Project: Hadoop HBase
> Issue Type: Improvement
> Components: client
> Reporter: Todd Lipcon
> Assignee: Mingjie Lai
> Fix For: 0.21.0
>
> Attachments: HBASE-2468-trunk.patch
>
>
> A couple different use cases cause storms of reads to META during startup.
> For example, a large MR job will cause each map task to hit meta since it
> starts with an empty cache.
> A couple possible improvements have been proposed:
> - MR jobs could ship a copy of META for the table in the DistributedCache
> - Clients could prewarm cache by doing a large scan of all the meta for the
> table instead of random reads for each miss
> - Each miss could fetch ahead some number of rows in META
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