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https://issues.apache.org/jira/browse/OMID-73?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16098265#comment-16098265
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ASF GitHub Bot commented on OMID-73:
------------------------------------
Github user ebortnik commented on a diff in the pull request:
https://github.com/apache/incubator-omid/pull/12#discussion_r129017932
--- Diff:
hbase-client/src/main/java/org/apache/omid/transaction/TTable.java ---
@@ -132,7 +133,7 @@ public Result get(Transaction tx, final Get get) throws
IOException {
HBaseTransaction transaction = enforceHBaseTransactionAsParam(tx);
- final long readTimestamp = transaction.getStartTimestamp();
--- End diff --
Please add external comments about read and write timestamps, and how they
relate to visibility levels.
> Add Checkpoints and visibility levels
> -------------------------------------
>
> Key: OMID-73
> URL: https://issues.apache.org/jira/browse/OMID-73
> Project: Apache Omid
> Issue Type: New Feature
> Reporter: Ohad Shacham
> Assignee: Ohad Shacham
>
> A checkpoint is a point in a transaction where every write occurs after the
> checkpoint may not be visible by the transaction.
> The visibility is defined by the following visibility levels:
> SNAPSHOT - returns the last written key by the transaction, in case one
> exists, otherwise, returns the key from the transaction snapshot.
> SNAPSHOT_EXCLUDE_CURRENT - returns the last written key by the transaction
> that was written before the last checkpoint, in case one exists, otherwise,
> returns the key from the transaction snapshot.
> SNAPSHOT_ALL - returns all the versions written by the transaction including
> the one in the transaction snapshot.
> This feature is needed for Phoenix both for upsert operations and for correct
> rollback of the secondary index on transaction abort.
> Explanations for this feature can be seen in [TEPHRA-96].
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