I supposed it was an answer to my mail but not sure... please keep CC'ed people, it is easier to follow threads (at least for me) 2010/11/12 Vitalii Tymchyshyn <tivv00@xxxxxxxxx>: > I'd say there are two Qs here: > > 1) Modify costs based on information on how much of the table is in cache. > It would be great if this can be done, but I'd prefer to have it as admin > knobs (because of plan stability). May be both admin and automatic ways can > be followed with some parallel (disableable) process modify knobs on admin > behalf. In this case different strategies to automatically modify knobs can > be applied. OS cache is usualy stable enough to keep your plans stable too, I think. > > 2) Modify costs for part of table retrieval. Then you need to define "part". > Current ways are partitioning and partial indexes. Some similar to partial > index thing may be created, that has only "where" clause and no data. But > has statistics and knobs (and may be personal bufferspace if they are > introduced). I don't like to gather data about "last X percents" or like, > because it works only in clustering and it's hard for optimizer to decide if > it will be enough to scan only this percents for given query. Modifying random_page_cost and sequential_page_cost thanks to statistics about cached blocks can be improved if we know the distribution. It does not mean : we know we have last 15% in cache, and we are goign to request those 15%. > > Best regards, Vitalii Tymchyshyn > > -- > Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance > -- Cédric Villemain 2ndQuadrant http://2ndQuadrant.fr/ ; PostgreSQL : Expertise, Formation et Support -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
