Added to TODO: * Improve performance for queries with many columns
We already have an item for tables with many columsn. --------------------------------------------------------------------------- Tom Lane wrote: > <[EMAIL PROTECTED]> writes: > >> As long as we are playing "who's is biggest", I have one with 900+ > >> attributes (normalized) but there is a big warning - if you have a > >> query that returns hundreds of columns it will be very, very slow. > > > Is the SELECT * the only circumstance? That is, if you specify a small > > number of columns, does the response improve even though the table > > actually has that large number of columns but is only be asked to supply > > a column-limited result set? > > IIRC, the worst problems that Steve's profile exposed were associated > with large numbers of columns in a SELECT result --- there are some > doubly nested loops that take time O(N^2) in the number of columns. > But I would not be surprised if some of those loops get invoked on the > underlying table, too, depending on what your query looks like exactly. > > This is all eminently fixable, it's just a matter of someone finding > some round tuits ... for most people it doesn't seem like a > high-priority problem, since you won't notice it till you get into the > hundreds of columns ... > > regards, tom lane > > ---------------------------(end of broadcast)--------------------------- > TIP 5: Have you checked our extensive FAQ? > > http://www.postgresql.org/docs/faqs/FAQ.html > -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]