Re: mysql_fdw trouble - Mailing list pgsql-general

On 10/29/2015 12:10 PM, Dane Foster wrote:

On Thu, Oct 29, 2015 at 3:01 PM, John R Pierce <pierce@hogranch.com
<mailto:pierce@hogranch.com>> wrote:

    On 10/29/2015 11:20 AM, Dane Foster wrote:

    ​I think you are correct about mysql_fdw "... sending the trim()
    checks for remote execution" because according to the docs:

    "The latest version will push-down the foreign table where clause
    to the foreign server. The where condition on the foreign table
    will be executed on the foreign server hence there will be fewer
    rows to to bring across to PostgreSQL. This is a performance feature."

    the alternative would be to fetch the whole table across the FDW
    interface, then run the where locally, for a large table where
    you're only selecting a few rows, this would be very painful.

    I guess using mysql_fdw is a no-go for my data migration needs.

    or, rewrite that WHERE clause to be mysql compatible.

Easier said than done because the LENG​TH and TRIM functions both exist
in MySQL but I guess under the covers in PostgreSQL btrim is being
invoked when TRIM is called therefore that is what is being "pushed
down" to the MySQL and there is nothing I can do about that.

I guess I could leave out the call to trim, and copy the data into a
temp table on the PostgreSQL side, and blah blah blah. My point being
why should I have to jump through hoops because mysql_fdw is broken?
I'll just go back to writing the migration script as a PHP program
because if mysql_fdw didn't exist that's what I would have to do anyway.

Remember you are using a Beta version of Postgres, so it is not entirely unexpected that things might be broken, especially when working with non-core extensions. In the spirit of testing, that Beta implies, why not help fix mysql_fdw by filing an issue? If you already have, my apologies.

    --
    john r pierce, recycling bits in santa cruz

​Dane​

--
Adrian Klaver
adrian.klaver@aklaver.com