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https://issues.apache.org/jira/browse/HBASE-2023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12838145#action_12838145
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Jean-Daniel Cryans commented on HBASE-2023:
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@Karthik
That sounds good, only one client hitting the META/ROOT region at a time while
not blocking others for seconds.
> Client sync block can cause 1 thread of a multi-threaded client to block all
> others
> -----------------------------------------------------------------------------------
>
> Key: HBASE-2023
> URL: https://issues.apache.org/jira/browse/HBASE-2023
> Project: Hadoop HBase
> Issue Type: Bug
> Affects Versions: 0.20.2
> Reporter: ryan rawson
>
> Take a highly multithreaded client, processing a few thousand requests a
> second. If a table goes offline, one thread will get stuck in
> "locateRegionInMeta" which is located inside the following sync block:
> synchronized(userRegionLock){
> return locateRegionInMeta(META_TABLE_NAME, tableName, row,
> useCache);
> }
> So when other threads need to find a region (EVEN IF ITS CACHED!!!) it will
> encounter this sync and wait.
> This can become an issue on a busy thrift server (where I first noticed the
> problem), one region offline can prevent access to all other regions!
> Potential solution: narrow this lock, or perhaps just get rid of it
> completely.
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