On 10/29/2015 12:10 PM, Dane Foster wrote:
On Thu, Oct 29, 2015 at 3:01 PM, John R Pierce <pierce@xxxxxxxxxxxx
<mailto:pierce@xxxxxxxxxxxx>> 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 LENGTH 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@xxxxxxxxxxx
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