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https://issues.apache.org/jira/browse/OMID-90?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16644679#comment-16644679
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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_r223973121
--- Diff:
hbase-client/src/main/java/org/apache/omid/transaction/SnapshotFilterImpl.java
---
@@ -181,22 +179,44 @@ public CommitTimestamp locateCellCommitTimestamp(long
cellStartTimestamp, long e
// 2) Then check the commit table
// If the data was written at a previous epoch, check whether
the transaction was invalidated
- Optional<CommitTimestamp> commitTimeStamp =
commitTableClient.getCommitTimestamp(cellStartTimestamp).get();
- if (commitTimeStamp.isPresent()) {
- return commitTimeStamp.get();
+ boolean invalidatedByOther = false;
+ Optional<CommitTimestamp> commitTimestampFromCT =
commitTableClient.getCommitTimestamp(cellStartTimestamp).get();
+ if (commitTimestampFromCT.isPresent()) {
+ if (isLowLatency && !commitTimestampFromCT.get().isValid())
+ invalidatedByOther = true;
+ else
+ return commitTimestampFromCT.get();
}
// 3) Read from shadow cell
- commitTimeStamp =
readCommitTimestampFromShadowCell(cellStartTimestamp, locator);
+ Optional<CommitTimestamp> commitTimeStamp =
readCommitTimestampFromShadowCell(cellStartTimestamp, locator);
if (commitTimeStamp.isPresent()) {
return commitTimeStamp.get();
}
+ // In case of LL, if found invalid ct cell, still must check
sc in stage 3 then return
--- End diff --
Please add this comment: "This check is not needed in a non low latency
mode, since during post commit, the client keeps the entry in the commit table
when persisting the commit was done after the TSO lost its lease."
> 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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