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Date: Tue, 25 Jun 2013 19:50:20 +0000 (UTC)
From: "rahul gidwani (JIRA)" <jira@apache.org>
To: dev@hbase.apache.org
Message-ID: <JIRA.12654793.1372189765357.172987.1372189820154@arcas>
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Subject: [jira] [Created] (HBASE-8806) Row locks are acquired repeatedly in
 HRegion.doMiniBatchMutation for duplicate rows.
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rahul gidwani created HBASE-8806:
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             Summary: Row locks are acquired repeatedly in HRegion.doMiniBatchMutation for duplicate rows.
                 Key: HBASE-8806
                 URL: https://issues.apache.org/jira/browse/HBASE-8806
             Project: HBase
          Issue Type: Bug
          Components: regionserver
    Affects Versions: 0.94.5
            Reporter: rahul gidwani
             Fix For: 0.98.0, 0.95.0, 0.94.0


If we already have the lock in the doMiniBatchMutation we don't need to re-acquire it. The solution would be to keep a cache of the rowKeys already locked for a miniBatchMutation and If we already have the 
rowKey in the cache, we don't repeatedly try and acquire the lock.  A fix to this problem would be to keep a set of rows we already locked and not try to acquire the lock for these rows.  

We have tested this fix in our production environment and has improved replication performance quite a bit.  We saw a replication batch go from 3+ minutes to less than 10 seconds for batches with duplicate row keys.

static final int ACQUIRE_LOCK_COUNT = 0;

  @Test
  public void testRedundantRowKeys() throws Exception {

    final int batchSize = 100000;
    
    String tableName = getClass().getSimpleName();
    Configuration conf = HBaseConfiguration.create();
    conf.setClass(HConstants.REGION_IMPL, MockHRegion.class, HeapSize.class);
    MockHRegion region = (MockHRegion) TestHRegion.initHRegion(Bytes.toBytes(tableName), tableName, conf, Bytes.toBytes("a"));

    List<Pair<Mutation, Integer>> someBatch = Lists.newArrayList();
    int i = 0;
    while (i < batchSize) {
      if (i % 2 == 0) {
        someBatch.add(new Pair<Mutation, Integer>(new Put(Bytes.toBytes(0)), null));
      } else {
        someBatch.add(new Pair<Mutation, Integer>(new Put(Bytes.toBytes(1)), null));
      }
      i++;
    }
    long startTime = System.currentTimeMillis();
    region.batchMutate(someBatch.toArray(new Pair[0]));
    long endTime = System.currentTimeMillis();
    long duration = endTime - startTime;
    System.out.println("duration: " + duration + " ms");
    assertEquals(2, ACQUIRE_LOCK_COUNT); <--- should only try and acquire the lock twice.
  }

  @Override
  public Integer getLock(Integer lockid, byte[] row, boolean waitForLock) throws IOException {
    ACQUIRE_LOCK_COUNT++;
    return super.getLock(lockid, row, waitForLock);
  }


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