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From "Keith Turner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-1833) MultiTableBatchWriterImpl.getBatchWriter() is not performant for multiple threads
Date Thu, 07 Nov 2013 18:57:19 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-1833?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13816271#comment-13816271
] 

Keith Turner commented on ACCUMULO-1833:
----------------------------------------

[~elserj] a functional test that checks the behavior of getBatchWriter() after renaming and
deleting tables would be really good.  Could also check basics like read and write.  Could
do this in addition to or instead of a random walk test.   You could easily add a node for
MTBW to the concurrent random walk test which operates on 5 tables.  Howerver you will not
get a sense of correctness of the MTBW itself.  That test just tries to make Accumulo fall
over and die.   The shard random walk test uses multiple tables (and index and document table)
and does rename them so it would be a good candidate to look into using the MTBW.

> MultiTableBatchWriterImpl.getBatchWriter() is not performant for multiple threads
> ---------------------------------------------------------------------------------
>
>                 Key: ACCUMULO-1833
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1833
>             Project: Accumulo
>          Issue Type: Improvement
>    Affects Versions: 1.5.0, 1.6.0
>            Reporter: Chris McCubbin
>         Attachments: ACCUMULO-1833-test.patch, ZooKeeperThreadUtilization.png
>
>
> This issue comes from profiling our application. We have a MultiTableBatchWriter created
by normal means. I am attempting to write to it with multiple threads by doing things like
the following:
> {code}
> batchWriter.getBatchWriter(table).addMutations(mutations);
> {code}
> In my test with 4 threads writing to one table, this call is quite inefficient and results
in a large performance degradation over a single BatchWriter.
> I believe the culprit is the fact that the call is synchronized. Also there is the possibility
that the zookeeper call to Tables.getTableState on every call is negatively affecting performance:
> {code}
>   @Override
>   public synchronized BatchWriter getBatchWriter(String tableName) throws AccumuloException,
AccumuloSecurityException, TableNotFoundException {
>     ArgumentChecker.notNull(tableName);
>     String tableId = Tables.getNameToIdMap(instance).get(tableName);
>     if (tableId == null)
>       throw new TableNotFoundException(tableId, tableName, null);
>     
>     if (Tables.getTableState(instance, tableId) == TableState.OFFLINE)
>       throw new TableOfflineException(instance, tableId);
>     
>     BatchWriter tbw = tableWriters.get(tableId);
>     if (tbw == null) {
>       tbw = new TableBatchWriter(tableId);
>       tableWriters.put(tableId, tbw);
>     }
>     return tbw;
>   }
> {code}
> I recommend moving the synchronized block to happen only if the batchwriter is not present,
and also only checking if the table is online at that time:
> {code}
>   @Override
>   public BatchWriter getBatchWriter(String tableName) throws AccumuloException, AccumuloSecurityException,
TableNotFoundException {
>     ArgumentChecker.notNull(tableName);
>     String tableId = Tables.getNameToIdMap(instance).get(tableName);
>     if (tableId == null)
>       throw new TableNotFoundException(tableId, tableName, null);
>     BatchWriter tbw = tableWriters.get(tableId);
>     if (tbw == null) {
>       if (Tables.getTableState(instance, tableId) == TableState.OFFLINE)
>           throw new TableOfflineException(instance, tableId);
>       tbw = new TableBatchWriter(tableId);
>       synchronized(tableWriters){
>           //only create a new table writer if we haven't been beaten to it.
>           if (tableWriters.get(tableId) == null)      
>               tableWriters.put(tableId, tbw);
>       }
>     }
>     return tbw;
>   }
> {code}



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