evgeny gridasov wrote: > Hi Everybody. > > I am going to replace some 'select count(*) from ... where ...' queries > which run on large tables (10M+ rows) with something like > 'explain select * from ... where ....' and parse planner output after that > to find out its forecast about number of rows the query is going to retrieve. > > Since my users do not need exact row count for large tables, this will > boost performance for my application. I ran some queries with explain and > explain analyze then. If i set statistics number for the table about 200-300 > the planner forecast seems to be working very fine. > > My questions are: > 1. Is there a way to interact with postgresql planner, other than 'explain > ...'? An aggregate query like 'select estimate_count(*) from ...' would > really help =)) > 2. How precise is the planner row count forecast given for a complex query > (select with 3-5 joint tables,aggregates,subselects, etc...)? > > I think that this has been done before. Check the list archives (I believe it may have been Michael Fuhr?)
ah, check this: http://archives.postgresql.org/pgsql-sql/2005-08/msg00046.php -- _______________________________ This e-mail may be privileged and/or confidential, and the sender does not waive any related rights and obligations. Any distribution, use or copying of this e-mail or the information it contains by other than an intended recipient is unauthorized. If you received this e-mail in error, please advise me (by return e-mail or otherwise) immediately. _______________________________ ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
