Re: planner/optimizer question

Gary,

> In this example the statistics don't matter. The plans used were the same
for
> MSSQL and Postgres. I was trying to eliminate the difference in plans
> between the two, which obviously does make a difference, sometimes in
> MSSQL favour and sometimes the other way round. Both systems, having
> decided to do the same index scan, took noticably different times. The
> Postgres database was fully vacuumed and analysed anyway.

It's also quite possble the MSSQL simply has more efficient index scanning
implementation that we do.    They've certainly had incentive; their storage
system sucks big time for random lookups and they need those fast indexes.
(just try to build a 1GB adjacency list tree on SQL Server.   I dare ya).

Certainly the fact that MSSQL is essentially a single-user database makes
things easier for them.    They don't have to maintain multiple copies of the
index tuples in memory.    I think that may be our main performance loss.

--
-Josh Berkus
 Aglio Database Solutions
 San Francisco