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https://issues.apache.org/jira/browse/ACCUMULO-1833?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13817329#comment-13817329
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Josh Elser commented on ACCUMULO-1833:
--------------------------------------
True, but I will state that the entire premise of this ticket is that we're
changing the semantics of MTBW. The "common" use case that its API allows is
for highly concurrent access and, as such, the semantics of it have changed.
I'll look into some sort of notification mechanism like you suggested.
> 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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