On Fri, Dec 17, 2010 at 3:03 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Heikki Linnakangas <heikki.linnakan...@enterprisedb.com> writes: >> On 17.12.2010 21:32, Robert Haas wrote: >>> I guess the question is whether it's right to conflate "table is >>> unlogged" with "LSN is fake". It's not immediately obvious to me that >>> those concepts are isomorphic, although though the reverse isn't >>> obvious to me either. > >> The buffer manager only needs to know if it has to flush the WAL before >> writing the page to disk. The flag just means that the buffer manager >> never needs to do that for this buffer. You're still free to store a >> real LSN there if you want to, it just won't cause any WAL flushes. > > Yeah. I think that BM_UNLOGGED might be a poor choice for the flag name, > just because it overstates what the bufmgr needs to assume. It might be > better to reverse the flag sense, and have a new flag that *is* set if > the page contains an LSN that we have to check against WAL.
I was actually thinking of adding BM_UNLOGGED even before this discussion, because that would allow unlogged buffers to be excluded from non-shutdown checkpoints. We could add two flags with different semantics that take on, under present rules, the same value, but I'd be disinclined to burn the extra bit without a concrete need. -- 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
