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https://issues.apache.org/jira/browse/HBASE-17361?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15800396#comment-15800396
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Yu Li commented on HBASE-17361:
-------------------------------
Thanks [~enis] for chiming in. Linking HBASE-17372 and this one together for
consensus.
> Make HTable thread safe
> -----------------------
>
> Key: HBASE-17361
> URL: https://issues.apache.org/jira/browse/HBASE-17361
> Project: HBase
> Issue Type: Improvement
> Reporter: Yu Li
> Assignee: Yu Li
> Attachments: HBASE-17361.patch, HBASE-17361.patch
>
>
> Currently HTable is marked as NOT thread safe, and this JIRA target at
> improving this to take better usage of the thread-safe BufferedMutator.
> Some findings/work done:
> If we try to do put to the same HTable instance in parallel, there'll be
> problem, since now we have {{HTable#getBufferedMutator}} like
> {code}
> BufferedMutator getBufferedMutator() throws IOException {
> if (mutator == null) {
> this.mutator = (BufferedMutatorImpl) connection.getBufferedMutator(
> new BufferedMutatorParams(tableName)
> .pool(pool)
> .writeBufferSize(connConfiguration.getWriteBufferSize())
> .maxKeyValueSize(connConfiguration.getMaxKeyValueSize())
> );
> }
> mutator.setRpcTimeout(writeRpcTimeout);
> mutator.setOperationTimeout(operationTimeout);
> return mutator;
> }
> {code}
> And {{HTable#flushCommits}}:
> {code}
> void flushCommits() throws IOException {
> if (mutator == null) {
> // nothing to flush if there's no mutator; don't bother creating one.
> return;
> }
> getBufferedMutator().flush();
> }
> {code}
> For {{HTable#put}}
> {code}
> public void put(final Put put) throws IOException {
> getBufferedMutator().mutate(put);
> flushCommits();
> }
> {code}
> If we launch multiple threads to put in parallel, below sequence might happen
> because {{HTable#getBufferedMutator}} is not thread safe:
> {noformat}
> 1. ThreadA runs to getBufferedMutator and finds mutator==null
> 2. ThreadB runs to getBufferedMutator and finds mutator==null
> 3. ThreadA initialize mutator to instanceA, then calls mutator#mutate,
> adding one put (putA) into {{writeAsyncBuffer}}
> 4. ThreadB initialize mutator to instanceB
> 5. ThreadA runs to flushCommits, now mutator is instanceB, it calls
> instanceB's flush method, putA is lost
> {noformat}
> After fixing this, we will find quite some contention on
> {{BufferedMutatorImpl#flush}}, so more efforts required to make HTable thread
> safe but with good performance meanwhile.
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