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https://issues.apache.org/jira/browse/OMID-90?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=16543619#comment-16543619
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Lianghong Xu commented on OMID-90:
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Hi [~ohads] [~ebortnik] I just did an initial evaluation with Omid Low Latency
version with YCSB. However, the result in terms of throughput and latency seems
similar to the original Omid. I guess maybe there is something I'm missing? I
was using the default configs except that I set "lowLatency: true" to be true
in omid-server-configuration.yml. I think that should be enough to turn on the
low latency mode, right?
The YCSB workload we used has a read/write ratio of 80/20 with uniform dist.
Please let us know if you have any suggestions on tuning.
Thanks,
Lianghong
> 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: New Feature
>Reporter: Ohad Shacham
>Assignee: Yonatan Gottesman
>Priority: Major
> Attachments: OmidCloud-VLDB.pdf
>
>
> 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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