Re: properly detecting cases where handler can silently overwrite rows

Hello all,

Does anyone have any thoughts on this?

Thanks
-Zardosht

On Tue, Feb 26, 2013 at 4:47 PM, Zardosht Kasheff <[email protected]> wrote:
> Hello all,
>
> For a bunch of statements, "replace into", "replace into ... select",
> "load data... replace", we sometimes do not follow the protocol of
> return an error if we see a duplicate key so that a subsequent update
> can overwrite the row. Instead, we have handler::write_row silently
> overwrite the data and report success.
>
> The trouble we have is properly detecting when we are indeed allowed
> to silently overwrite the row. What we have been doing is checking
> (thd->lex->duplicates == DUP_REPLACE).
>
> We recently found what seems like a corner case where this does not
> work. During replication on a slave, if slave_exec_mode is set to
> IDEMPOTENT, then thd->lex->duplicates is set to DUP_REPLACE, but the
> operation is not just a silent overwrite. The operation works like an
> insert on duplicate key update, where the updated row is dependent on
> the existing row and the inserted row.
>
> My questions:
>  - why is DUP_REPLACE being set in this case in replication?
>  - What is the proper way to determine when we can safely silently
> overwrite an existing row. We already check for having a binary log in
> row format and for triggers. It seems checking thd->lex->DUP_REPLACE
> is not sufficient.
>
> Thanks
> -Zardosht

-- 
MySQL Internals Mailing List
For list archives: http://lists.mysql.com/internals
To unsubscribe:    http://lists.mysql.com/internals