On Sun, 2010-04-25 at 12:43 -0400, Tom Lane wrote: > Simon Riggs <si...@2ndquadrant.com> writes: > > [ v2 patch ] > > BTW, while I'm looking at this, why bother with the separate > KnownAssignedXidsValid[] array? Wouldn't it be cheaper > (certainly so in storage, probably so in access/update times) > to have just the KnownAssignedXids[] array and store > InvalidTransactionId in unused entries?
Well, that was exactly my first design. Heikki came up with the additional array and I think it is an inspired suggestion, because it allows the search() to use a simple binary search. I attempted to write the binary-search-with-holes and it was going to be very ugly code, so I went for another algorithm which was also quite cool, but not as cool as Heikki's idea - which I was going to give credit for. The array adds 520*max_connections bytes of shared memory, but seems a good tradeoff for the additional performance it allows. I guess we could use a bit array, but that's slower to access. The bit array would be 9*max_connections bytes of shared memory, so a 40kB saving. -- Simon Riggs www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
