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From "Stanislav Lukyanov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IGNITE-8550) CacheAbstractJdbcStore expects merge to always return 1 but MySQL may also return 2 or 0
Date Tue, 29 Jan 2019 15:14:00 GMT

    [ https://issues.apache.org/jira/browse/IGNITE-8550?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16755105#comment-16755105
] 

Stanislav Lukyanov commented on IGNITE-8550:
--------------------------------------------

[~smoldachev] Big thanks for looking into this! I'm afraid this PR needs some changes though.

First, MySQL spec says that valid values are 0, 1 and 2, not just 1 and 2 - see the Description
of the JIRA. Need to also allow that.

Second, adding a method to a Java interface is an incompatible change. Any implementations
of `JdbcDialect` that may exist out there will stop working with this change.
One way to approach that would be to use a Java 8's `default` method that would return 1,
and only override it for MySQL.

Third, we need tests. Let's add test cases that would do inserts of new rows, updates of existing
rows and set the row to the same value (i.e. check all three cases for which MySQL return
different values). Without the fix some of the MySQL test cases will fail, and with the fix
they will pass.

Finally, let's add a comment to the MySQL implementation that would explain how we can get
different values from the `INSERT`.

If you have questions - feel free to ask, I'll be happy to assist.

> CacheAbstractJdbcStore expects merge to always return 1 but MySQL may also return 2 or
0
> ----------------------------------------------------------------------------------------
>
>                 Key: IGNITE-8550
>                 URL: https://issues.apache.org/jira/browse/IGNITE-8550
>             Project: Ignite
>          Issue Type: Bug
>          Components: cache
>            Reporter: Stanislav Lukyanov
>            Assignee: Moldachev Sergey
>            Priority: Minor
>              Labels: newbie
>             Fix For: 2.8
>
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> CacheAbstractJdbcStore.write attempts to execute a merge update if it is available, and
expects the merge to always return 1 (as the number of updated entries is always 1).
> However, MySQL's `INSERT ... ON DUPLICATE KEY UPDATE` (https://dev.mysql.com/doc/refman/8.0/en/insert-on-duplicate.html)
may return 0 or 2, depending on what was updated:
> {quote}With ON DUPLICATE KEY UPDATE, the affected-rows value per row is 1 if the row
is inserted as a new row, 2 if an existing row is updated, and 0 if an existing row is set
to its current values.{quote}
> Because of that, CacheAbstractJdbcStore may report a false warning.
> Need to consider either removing the warning or special-case the MySQL dialect to allow
to return values other than 1.



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