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https://issues.apache.org/jira/browse/HBASE-8171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13609423#comment-13609423
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Jean-Daniel Cryans commented on HBASE-8171:
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We had a longish discussion about this too here:
https://issues.apache.org/jira/browse/HBASE-6841
My opinion is that pre-fetching is bad for most use cases the way it is
implemented and I prefer to run without it in production.
> Perf issue with multiple client threads trying to prefetch Region Cache from
> META
> ---------------------------------------------------------------------------------
>
> Key: HBASE-8171
> URL: https://issues.apache.org/jira/browse/HBASE-8171
> Project: HBase
> Issue Type: Bug
> Affects Versions: 0.89-fb, 0.94.3, 0.94.5
> Reporter: Amitanand Aiyer
> Assignee: Amitanand Aiyer
>
> HBaseClient maintains a cache of Regions to region locations that gets
> cleared whenever the RS that the client talks to is unresponsive.
> This will result in the Client having to talk to META to fetch the region
> location before doing the get/put.
> https://issues.apache.org/jira/browse/HBASE-2468 introduces the feature to
> prewarm the cache, where the client gets some rows from META to warm the
> cache.
> This is a costly operation. And, it looks like all client threads that block
> on the regionLockObject, will go in and do the cache warmup; although the
> cache might have been already warmed up by an earlier thread.
> When there is a network issue going on, we see lots of Client threads
> blocking in locateRegionInMeta.
> The fix would be to check the cache again; before we do the prefetch after
> grabbing the lock. Currently, the client threads look in the cache at the
> begining of the method. But a lot could have changed while waiting for the
> regionLockObject.
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