On Tue, Jul 5, 2011 at 12:03 PM, Kevin Grittner <kevin.gritt...@wicourts.gov> wrote: > Robert Haas <robertmh...@gmail.com> wrote: > >> Well, as long as we can verify that OLDSERXID_MAX_PAGE has the >> same value for BLCKSZ=8K before and after this patch, I don't see >> any real downside to applying it. If, hypothetically, it's buggy, >> it's only going to break things for non-default block sizes which >> are, by your description, not correct right now anyway. > > Outside of a code comment, the entire patch consists of replacing > the definition of the OLDSERXID_MAX_PAGE macro. The old definition > is: > > (SLRU_PAGES_PER_SEGMENT * 0x10000 - 1) > > SLRU_PAGES_PER_SEGMENT is define to be 32. So this is: > > (32 * 0x10000) - 1 = 2097151 > > The new definition is the min of the old one and a value based on > BLCKSZ: > > (MaxTransactionId + 1) / OLDSERXID_ENTRIESPERPAGE - 1) > > Where "entries per page" is BLCKSZ / sizeof(uint64). > > For an 8K BLCKSZ this is: > > ((0xffffffff + 1) / 1024) - 1 = 4194303 > > So the macro is guaranteed to have the same value as it currently > does for BLCKSZ of 16KB or lower.
I went ahead and committed this. -- 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
