[jira] [Created] (HBASE-19260) Add lock back to avoid parallel accessing meta to locate region

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

Yu Li created HBASE-19260:
-----------------------------

             Summary: 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: 1.1.12, 2.0.0-alpha-3, 1.2.6, 1.3.1
            Reporter: Yu Li


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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