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https://issues.apache.org/jira/browse/OMID-58?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15895316#comment-15895316
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Francisco Perez-Sorrosal commented on OMID-58:
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Hey [~ohads]. There's no need to go to the TSO as we can do it from the Client
side. I started working on a fix for this in the past but I stopped cause I
realized that it would be better do first some refactoring to improve how we
manage the pre/post hooks for the AbstractTM and remove the
TransactionException from the interface exposed to the users. Anyways, I've put
in here the draft of what I did:
https://github.com/francisco-perez-sorrosal/incubator-omid/commit/2990ea706735a2b7f980c96cd266b174c5ab3133
The round-trip to the database could be avoided if we store the LWM in ZK and
we put a watcher in the client, but this could potentially create more problems.
> Snapshot isolation violation in read only transactions
> ------------------------------------------------------
>
> Key: OMID-58
> URL: https://issues.apache.org/jira/browse/OMID-58
> Project: Apache Omid
> Issue Type: Bug
> Reporter: Ohad Shacham
>
> Read only transactions in snapshot isolation cannot conflict with any other
> transaction. Therefore, the commit process does not contact the TSO and mark
> the transaction as committed.
> This can cause to snapshot isolation violation in cases where the coprocessor
> deletes information from HBase that changes the snapshot of an inflight read
> only transaction t. t in this case will be marked as committed, even thought
> it did not read a consistent snapshot.
> t would be aborted if the commit process would contact the tso because its
> read timestamp is smaller than the low water mark.
> A solution for this would be to contact the TSO, check the low water mark,
> identify in the requestProcessor that the transaction is read only, and
> immediately return a result using the reply processor. This will reduce the
> latency (v.s. the regular flow) of read only transactions, while maintaining
> snapshot isolation.
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