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