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From "Amitanand Aiyer (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-8476) locateRegionInMeta should check the cache before doing the prefetch
Date Wed, 01 May 2013 17:44:16 GMT
Amitanand Aiyer created HBASE-8476:
--------------------------------------

             Summary: locateRegionInMeta should check the cache before doing the prefetch
                 Key: HBASE-8476
                 URL: https://issues.apache.org/jira/browse/HBASE-8476
             Project: HBase
          Issue Type: Bug
            Reporter: Amitanand Aiyer
            Assignee: Amitanand Aiyer
            Priority: Minor
             Fix For: 0.89-fb, 0.95.2


locateRegionInMeta uses a regionLockObject to synchronize all accesses to prefetch the RegionCache.

         synchronized (regionLockObject) {
            // If the parent table is META, we may want to pre-fetch some
            // region info into the global region cache for this table.
            if (Bytes.equals(parentTable, HConstants.META_TABLE_NAME) &&
                (getRegionCachePrefetch(tableName)) )  {
              prefetchRegionCache(tableName, row);
            }

            // Check the cache again for a hit in case some other thread made the
            // same query while we were waiting on the lock. If not supposed to
            // be using the cache, delete any existing cached location so it won't
            // interfere.
            if (useCache) {
              location = getCachedLocation(tableName, row);
              if (location != null) {
                return location;
              }
            } else {
              deleteCachedLocation(tableName, row);
            }

 

However, for this to be effective, we need to check the cache as soon as we grab the lock;
before doing the prefetch. Checking the cache after doing the prefetch does not help the current
thread, in case another thread has done the prefetch.

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