Simon Riggs wrote: > On Fri, 2009-12-04 at 07:12 -0500, Bruce Momjian wrote: > > > I think the hint bit has to be added to the item pointer, by using the > > offset bits that are already zero, according to Greg Stark. That > > solution leads to easy programming, no expanding hint bit array, and it > > is backward compatible so doesn't cause problems for pg_migrator. > > Seems like a reasonable way forward. > > As I pointed out here > http://archives.postgresql.org/pgsql-hackers/2009-12/msg00056.php > we only need to use 3 bits not 4, but it does limit tuple length to 4096 > for all block sizes. (Two different options there for doing that). > > An added advantage of this approach is that the cachelines for the item > pointer array will already be in CPU cache, so there is no additional > access time when we set the hint bits when they are moved to their new > position. > > I should also point out that removing 4 bits from the tuple header would > allow us to get rid of t_infomask2, reducing tuple length by a further 2 > bytes.
Wow, that is a nice win. Does alignment allow us to actually use that space? -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
