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

["Joydeep Sen Sarma (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-2023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12788157#action_12788157 ] 

Joydeep Sen Sarma commented on HBASE-2023:
------------------------------------------

i am looking at some pauses while loading data in and trying to figure out if this is applicable. we have multiple machines loading data - each multithreaded - each thread writing to a different range. all get paused at the same times once in a while. there's no cpu/io going on the region servers when this happens. (next time i reproduce - i will get a jstack dump on the regionservers).

can this happen on region splits? (I sure wasn't going any table offline/online during the test).

> 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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