2015-10-20 8:55 GMT+02:00 Thomas Kellerer <spam_ea...@gmx.net>: > Jonathan Rogers schrieb am 17.10.2015 um 04:14: > >>> Yes, I have been looking at both plans and can see where they diverge. > >>> How could I go about figuring out why Postgres fails to see the large > >>> difference in plan execution time? I use exactly the same parameters > >>> every time I execute the prepared statement, so how would Postgres come > >>> to think that those are not the norm? > >> > >> PostgreSQL does not consider the actual query execution time, it only > >> compares its estimates for there general and the custom plan. > >> Also, it does not keep track of the parameter values you supply, > >> only of the average custom plan query cost estimate. > > > > OK, that makes more sense then. It's somewhat tedious for the purpose of > > testing to execute a prepared statement six times to see the plan which > > needs to be optimized. Unfortunately, there doesn't seem to be any way > > to force use of a generic plan in SQL based on Pavel Stehule's reply. > > > If you are using JDBC the threshold can be changed: > > https://jdbc.postgresql.org/documentation/94/server-prepare.html > > https://jdbc.postgresql.org/documentation/publicapi/org/postgresql/PGStatement.html#setPrepareThreshold%28int%29 > > As I don't think JDBC is using anything "exotic" I would be surprised if > this > can't be changed with other programming environments also. >
This is some different - you can switch between server side prepared statements and client side prepared statements in JDBC. It doesn't change the behave of server side prepared statements in Postgres. Pavel > > Thomas > > > > -- > Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance >
