I know that there haven been many discussions on the slowness of count(*) even when an index is involved because the visibility of the rows has to be checked. In the past I have seen many suggestions about using triggers and tables to keep track of counts and while this works fine in a situation where you know what the report is going to be ahead of time, this is simply not an option when an unknown WHERE clause is to be used (dynamically generated). I ran into a fine example of this when I was searching this mailing list, "Searching in 856,646 pages took 13.48202 seconds. Site search powered by PostgreSQL 8.3." Obviously at some point count(*) came into play here because the site made a list of pages (1 2 3 4 5 6 > next). I very commonly make a list of pages from search results, and the biggest time killer here is the count(*) portion, even worse yet, I sometimes have to hit the database with two SELECT statements, one with OFFSET and LIMIT to get the page of results I need and another to get the amount of total rows so I can estimate how many pages of results are available. The point I am driving at here is that since building a list of pages of results is such a common thing to do, there need to be some specific high speed ways to do this in one query. Maybe an estimate(*) that works like count but gives an answer from the index without checking visibility? I am sure that this would be good enough to make a page list, it is really no big deal if it errors on the positive side, maybe the list of pages has an extra page off the end. I can live with that. What I can't live with is taking 13 seconds to get a page of results from 850,000 rows in a table. -Neil-
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