Robert Haas wrote: > > Well, I am not sure how we would turn the _space_ used for CRC on and > > off because you would have to rewrite the entire table/database to turn > > it on, which seems unfortunate. > > Well, presumably you're going to have to do some of that work anyway, > because even if the space is set aside you're still going to have to > read the page in, CRC it, and write it back out. However if the space > is not pre-allocated then you also have to deal with moving tuples to > other pages. But that problem is going to have to be dealt with > somewhere along the line no matter what we do, because if you're > upgrading an 8.3 or 8.4 system to 8.5, you need to add that space > sometime: either before migration (with a pre-upgrade utility), or > after migration (by some sort of page converter/tuple mover), or only > when/if enabling the CRC feature. > > One nice thing about making it the CRC feature's problem to make space > on each page is that people who don't want to use CRCs can still use > those extra 4 bytes/page for data. That might not be worth the code > complexity if we were starting from scratch, but I'm thinking that > most of the code complexity is a given if we want to also support > in-place upgrade.
My guess is we can find somewhere on a 8.4 heap/index page to add four bytes. -- 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
