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From "Samarth Jain (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-4051) Prevent out-of-order updates for mutable index updates
Date Fri, 28 Jul 2017 04:53:00 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-4051?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16104454#comment-16104454
] 

Samarth Jain commented on PHOENIX-4051:
---------------------------------------

bq. For an UPSERT VALUES, the timestamp is gotten from the server at commit time. This is
done so that the timestamp is consistent across all rows being written.

I don't think this actually happens in practice. In doMiniBatchMutation HBase tries to acquire
as many locks as it can. For the mutations in the batch for which it is able to acquire row
locks, it sets the same timestamp. For the ones it is not able to, it comes back and tries
to acquire locks again in which case the timestamp ends up being different from the first
attempt. This happens more often when there are concurrent updates to the same rows.

> Prevent out-of-order updates for mutable index updates
> ------------------------------------------------------
>
>                 Key: PHOENIX-4051
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-4051
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: James Taylor
>            Assignee: James Taylor
>         Attachments: PHOENIX-4051_v1.patch
>
>
> Out-of-order processing of data rows during index maintenance causes mutable indexes
to become out of sync with regard to the data table. Here's a simple example to illustrate
the issue:
> # Assume table T(K,V) and index X(V,K).
> # Upsert T(A, 1) at t10. Index updates: Put X(1,A) at t10.
> # Upsert T(A, 3) at t30. Index updates: Delete X(1,A) at t29, Put X(3,A) at t30.
> # Upsert T(A,2) at t20. Index updates: Delete X(1,A) at t19, Put X(2,A) at t20, Delete
X(2,A) at t29
> Ideally, we'd want to remove the Delete X(1,A) at t29 since this isn't correct in terms
of timeline consistency, but we can't do that with HBase without support for deleting/undoing
Delete markers. 
> The above is not what is occurring. Instead, when T(A,2) comes in, the Put X(2,A) will
occur at t20, but the Delete won't occur. This causes more index rows than data rows, essentially
making it invalid.
> A quick fix is to reset the timestamp of the data table mutations to the current time
within the preBatchMutate call, when the row is exclusively locked. This skirts the issue
because then timestamps won't overlap.



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