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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HBASE-19260) Add lock back to avoid parallel accessing meta to locate region
Date Wed, 15 Nov 2017 17:11:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-19260?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16253812#comment-16253812
] 

stack edited comment on HBASE-19260 at 11/15/17 5:10 PM:
---------------------------------------------------------

+1

I'd imagine this responsible for a bunch of loading on the RS hosting hbase:meta...


was (Author: stack):
+1



> Add lock back to avoid parallel accessing meta to locate region
> ---------------------------------------------------------------
>
>                 Key: HBASE-19260
>                 URL: https://issues.apache.org/jira/browse/HBASE-19260
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 1.3.1, 1.2.6, 2.0.0-alpha-3, 1.1.12
>            Reporter: Yu Li
>            Assignee: Yu Li
>         Attachments: HBASE-19260.patch, HBASE-19260.v2.patch
>
>
> In branch-0.98 we have below codes to avoid accessing meta in parallel in {{HConnectionManager}}:
> {code}
>           Result regionInfoRow;
>           // This block guards against two threads trying to load the meta
>           // region at the same time. The first will load the meta region and
>           // the second will use the value that the first one found.
>           if (useCache) {
>             if (TableName.META_TABLE_NAME.equals(parentTable) && usePrefetch
&&
>                 getRegionCachePrefetch(tableName)) {
>               synchronized (regionLockObject) {
>                 // Check the cache again for a hit in case some other thread made the
>                 // same query while we were waiting on the lock.
>                 ...
>               }
>             }
>           ...
> {code}
> while in HBASE-10018 we removed such logic along with region-location-prefetching. 
> We regard this as an unexpected behavior change and observed below phenomenon in our
product env:
> 1. Unnecessary connection setup to meta when multiple threads locating region in a client
process
> 2. Priority handler of the RS holding meta region exhausted, application keep retrying
and cause a vicious circle
> To resolve this problem, we propose to add the {{userRegionLock}} back and keep the behavior
in accordance with 0.98



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