[jira] Resolved: (HBASE-2023) Client sync block can cause 1 thread of a multi-threaded client to block all others

["stack (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-2023?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

stack resolved HBASE-2023.
--------------------------

       Resolution: Fixed
    Fix Version/s: 0.21.0
                   0.20.4
         Assignee: Karthik Ranganathan
     Hadoop Flags: [Reviewed]

Committed branch and trunk.  Thanks for the patch Karthik (I added you as contributor if you don't mind).

> 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
>            Assignee: Karthik Ranganathan
>             Fix For: 0.20.4, 0.21.0
>
>         Attachments: HBASE-2023_0.20.3.patch
>
>
> 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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