On Tue, Jan 14, 2014 at 4:23 PM, James Bottomley <james.bottom...@hansenpartnership.com> wrote: > Yes, that's what I was thinking: it's a cache. About how many files > comprise this cache? Are you thinking it's too difficult for every > process to map the files?
No, I'm thinking that would throw cache coherency out the window. Separate mappings are all well and good until somebody decides to modify the page, but after that point the database processes need to see the modified version of the page (which is, further, hedged about with locks) yet the operating system MUST NOT see the modified version of the page until the write-ahead log entry for the page modification has been flushed to disk. There's really no way to do that without having our own private cache. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
