diff --git a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionManager.java b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionManager.java index ff30ef45c9f..d6d6491f9cc 100644 --- a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionManager.java +++ b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionManager.java @@ -560,6 +560,9 @@ class ConnectionManager { // package protected for the tests ClusterStatusListener clusterStatusListener; + + private final Object metaRegionLock = new Object(); + // We have a single lock for master & zk to prevent deadlocks. Having // one lock for ZK and one lock for master is not possible: // When creating a connection to master, we need a connection to ZK to get @@ -1085,13 +1088,44 @@ class ConnectionManager { } if (tableName.equals(TableName.META_TABLE_NAME)) { - return this.registry.getMetaRegionLocation(); + return locateMeta(tableName, useCache, replicaId); } else { // Region not in the cache - have to go to the meta RS return locateRegionInMeta(tableName, row, useCache, retry, replicaId); } } + private RegionLocations locateMeta(final TableName tableName, + boolean useCache, int replicaId) throws IOException { + // HBASE-10785: We cache the location of the META itself, so that we are not overloading + // zookeeper with one request for every region lookup. We cache the META with empty row + // key in MetaCache. + byte[] metaCacheKey = HConstants.EMPTY_START_ROW; // use byte[0] as the row for meta + RegionLocations locations = null; + if (useCache) { + locations = getCachedLocation(tableName, metaCacheKey); + if (locations != null) { + return locations; + } + } + + // only one thread should do the lookup. + synchronized (metaRegionLock) { + // Check the cache again for a hit in case some other thread made the + // same query while we were waiting on the lock. + locations = getCachedLocation(tableName, metaCacheKey); + if (locations != null) { + return locations; + } + // Look up from zookeeper + locations = this.registry.getMetaRegionLocation(); + if (locations != null) { + cacheLocation(tableName, locations); + } + } + return locations; + } + /* * Search the hbase:meta table for the HRegionLocation * info that contains the table and row we're seeking.