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https://issues.apache.org/jira/browse/OMID-90?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16644682#comment-16644682
]
ASF GitHub Bot commented on OMID-90:
------------------------------------
Github user ohadshacham commented on a diff in the pull request:
https://github.com/apache/incubator-omid/pull/46#discussion_r223989230
--- Diff:
transaction-client/src/main/java/org/apache/omid/transaction/AbstractTransactionManager.java
---
@@ -350,6 +356,43 @@ private void
markReadOnlyTransaction(AbstractTransaction<? extends CellId> readO
}
+ private void commitLowLatencyTransaction(AbstractTransaction<? extends
CellId> tx)
+ throws RollbackException, TransactionException {
+ try {
+
+ long commitTs = tsoClient.commit(tx.getStartTimestamp(),
tx.getWriteSet(), tx.getConflictFreeWriteSet()).get();
+ boolean committed =
commitTableWriter.atomicAddCommittedTransaction(tx.getStartTimestamp(),commitTs);
+ if (!committed) {
+ // Transaction has been invalidated by other client
+ rollback(tx);
+
commitTableClient.completeTransaction(tx.getStartTimestamp());
+ rolledbackTxsCounter.inc();
+ throw new RollbackException("Transaction " +
tx.getTransactionId() + " got invalidated");
+ }
+ certifyCommitForTx(tx, commitTs);
+ updateShadowCellsAndRemoveCommitTableEntry(tx, postCommitter);
+
+ } catch (ExecutionException e) {
+ if (e.getCause() instanceof AbortException) { // TSO reports
Tx conflicts as AbortExceptions in the future
+ rollback(tx);
+ rolledbackTxsCounter.inc();
+ throw new RollbackException("Conflicts detected in tx
writeset", e.getCause());
+ }
+
+ if (e.getCause() instanceof ServiceUnavailableException ||
e.getCause() instanceof ConnectionException) {
+ errorTxsCounter.inc();
+ rollback(tx); // Rollback proactively cause it's likely
that a new TSOServer is now master
--- End diff --
the leader
> Reducing begin/commit latency by distributing the write to the commit table
> ---------------------------------------------------------------------------
>
> Key: OMID-90
> URL: https://issues.apache.org/jira/browse/OMID-90
> Project: Apache Omid
> Issue Type: Sub-task
> Reporter: Ohad Shacham
> Assignee: Yonatan Gottesman
> Priority: Major
> Attachments: OmidCloud-VLDB.pdf, omid90.patch
>
>
> Today, Omid's commits are done by the transaction manager. In order to
> efficiently write to the commit table, the transaction manager batches these
> writes. This optimization, even thought reduces the write time to HBase,
> significantly increases the begin and commit latency. The commit latency
> increases since a commit operation returns only after its commit timestamp
> was persisted in the commit table. And the begin latency increases since
> begin returns a transaction id that is also used by the transaction to
> identify its snapshot and therefore, begin returns only after all commits
> with commit id smaller than the begin id was persisted in the commit table.
> This is crucial, since a snapshot change during a transaction run may violate
> snapshot isolation.
>
> The idea of this feature is to distribute the commit by moving the write to
> the commit table from the server to the client. The transaction manager does
> conflict analysis and returns a commit timestamp. While the client atomically
> persists this commit in the commit table.
> This significantly reduces the begin and commit latency, since batching is
> not required anymore. A begin operation can immediately returns and a commit
> operation returns after conflict detection.
> This can introduce snapshot isolation violation since a slow client can
> commit and change other transaction's snapsho. Therefore, we use an
> invalidation technique which is similar to the one Omid uses today to
> maintain snapshot isolation in high availability mode.
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