hi,
i had a stored procedure in ms-sql server. this stored procedure gets a parameter (account-id), dose about 20 queries, fills some temporary tables, and finally, returns a few result-sets. this stored procedure converted to stored function in postgresql (9.1). the result-sets are being returned using refcursors. this stored function is logically, almost identical to the ms-sql stored procedure. a LOT of work had been done to make postgresql getting close to ms-sql speed (preparing temp-tables in advance, using "analyze" in special places inside the stored function in order to hint the optimizer that the temp-tables have very few records, thus eliminating unnecessary and expansive hash-join, and a lot more..). after all that, the stored function is running in a reasonable speed (normally ~60 milliseconds).
now, i run a test that simulates 20 simultaneous clients, asking for "account-id" randomly. once a client get a result, it immediately asks for another one. the test last 5 seconds. i use a connection pool (with Tomcat web-server). the pool is automatically increased to ~20 connections (as expected). the result is postgresql dose ~60 "account-id"s, whereas ms-sql dose ~330 "account-id"s. postgresql shows that each "account-id" took about 400-1000 msec ,which is so much slower than the ~60 msec of a single execution.
in a single execution postgresql may be less the twice slower than ms-sql, but in 20 simultaneous clients, it's about 6 times worse. why is that?
the hardware is one 4-core xeon. 8GB of ram. the database size is just a few GB's. centos-6.2.
do you think the fact that postgresql use a process per connection (instead of multi-threading) is inherently a weakness of postgrsql, regarding scale-up?
would it be better to limit the number of connections to something like 4, so that executions don't interrupt each other?
thanks in advance for any help!
