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https://issues.apache.org/jira/browse/OMID-90?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16644684#comment-16644684
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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_r223993765
--- Diff:
tso-server/src/main/java/org/apache/omid/tso/RequestProcessorSkipCT.java ---
@@ -0,0 +1,92 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.omid.tso;
+
+import com.google.inject.Inject;
+import org.apache.omid.metrics.MetricsRegistry;
+import org.jboss.netty.channel.Channel;
+
+import java.io.IOException;
+
+public class RequestProcessorSkipCT extends AbstractRequestProcessor {
+
+
+ private final ReplyProcessor replyProcessor;
+
+ private final LeaseManagement leaseManager;
+ private final Panicker panicker;
+ private final String tsoHostAndPort;
+
+ @Inject
+ RequestProcessorSkipCT(MetricsRegistry metrics,
+ TimestampOracle timestampOracle,
+ ReplyProcessor replyProcessor,
+ Panicker panicker,
+ LeaseManagement leaseManager,
+ TSOServerConfig config,
+ LowWatermarkWriter lowWatermarkWriter,
+ String tsoHostAndPort) throws IOException {
+ super(metrics, timestampOracle, panicker, config,
lowWatermarkWriter);
+ this.replyProcessor = replyProcessor;
+ this.tsoHostAndPort = tsoHostAndPort;
+ requestRing = disruptor.start();
+ this.leaseManager = leaseManager;
+ this.panicker = panicker;
+ }
+
+ private void commitSuicideIfNotMaster() {
+ if (!leaseManager.stillInLeasePeriod()) {
+ panicker.panic("Replica " + tsoHostAndPort + " lost mastership
whilst flushing data. Committing suicide");
+ }
+ }
+
+ @Override
+ public void forwardCommit(long startTimestamp, long commitTimestamp,
Channel c, MonitoringContext monCtx) {
+ commitSuicideIfNotMaster();
--- End diff --
Add a comment that his is required since returning commit results when the
TSO is not the leader might violate snapshot isolation. This is because we have
to guarantee that committing transaction from previous tso has to persist all
its data because a new transaction started by a new tso.
> 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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