On Thu, Apr 17, 2014 at 6:50 PM, Greg Stark <st...@mit.edu> wrote: > On Thu, Apr 17, 2014 at 4:48 PM, Peter Geoghegan <p...@heroku.com> wrote: >> Although I will add that not caching highly useful inner pages for the >> medium term, because that index isn't being used at all for 5 minutes >> probably is very bad. Using the 4,828 buffers that it would take to >> store all the inner pages (as in my large primary index example) to go >> store something else is probably penny wise and pound foolish. > > But there could easily be 20 unused indexes for every 1 index that is > being used.
Sure, but then there might not be. Obviously there is a trade-off to be made between recency and frequency. One interesting observation in the LRU-K paper is that for their test case, a pure LFU actually works very well, despite, as the authors acknowledge, being a terrible algorithm in the real world. That's because their test case is so simple, and concerns only one table/index, with a uniform distribution. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
