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https://issues.apache.org/jira/browse/HBASE-15648?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15248194#comment-15248194
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Mikhail Antonov commented on HBASE-15648:
-----------------------------------------
If things are in meta cache, that will be handled at the top of
#locateRegionInMeta()
Goes like this:
- first try to get cached location; if found, return
- grab lock for the regionName
- try cached location again in case someone who held the lock retrieved it
for us
- if still no luck, do a meta scan
> Reduce number of concurrent region location lookups when MetaCache entry is
> cleared
> -----------------------------------------------------------------------------------
>
> Key: HBASE-15648
> URL: https://issues.apache.org/jira/browse/HBASE-15648
> Project: HBase
> Issue Type: Sub-task
> Components: Client
> Affects Versions: 1.3.0
> Reporter: Mikhail Antonov
> Assignee: Mikhail Antonov
> Fix For: 1.3.0
>
> Attachments: HBASE-15648-branch-1.3.v1.patch
>
>
> It seems in HConnectionImplementation#locateRegionInMeta if region location
> is removed from the cache, with large number of client threads we could have
> many of them getting cache miss and doing meta scan, which looks unnecessary
> - we could empty mechanism similar to what we have in IdLock in HFileReader
> to fetch the block to cache, do ensure that if one thread is already looking
> up location for region R1, other threads who need it's location wait until
> first thread finishes his work.
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