>>> Alvaro Herrera <[EMAIL PROTECTED]> wrote: > Kevin Grittner wrote: > >> Note that the 150 disk writes were for the CREATE and the DROP. Does >> that mean that we'd actually shave 84 of 150 writes? > > Hmm, you'd shave more than 42 but not 84, because index entries are not > deleted until a later vacuum. (I'd say about 56 -- 42 plus the 14 heap > deletions). > >> Also, if you're looking to account for all the writes, it's worth >> noting that my test declared a one-column primary key (on an integer >> column) in the CREATE TEMPORARY TABLE statement. > > That probably makes up for the extra few writes that I didn't see in my > quick test. It sounds like you were counting the 8kB pages pushed from the PostgreSQL cache to the OS cache, and I was counting the 1kB blocks pushed from the OS cache to the RAID controller cache. By watching vmstat results after pushing this to a more-or-less steady state, I was probably picking up the results of autovacuum runs, but multiple writes to a single page were often combined by the OS. If we match, it's really just a coincidence. -Kevin
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