I assume this is 8.4 material. ---------------------------------------------------------------------------
Heikki Linnakangas wrote: > Tom Lane wrote: > > "Simon Riggs" <[EMAIL PROTECTED]> writes: > >> As regards the zero_damaged_pages question, I raised that some time ago > >> but we didn't arrive at an explicit answer. All I would say is we can't > >> allow invalid pages in the buffer manager at any time, whatever options > >> we have requested, otherwise other code will fail almost immediately. > > > > Yeah --- the proposed new bufmgr routine should probably explicitly zero > > the content of the buffer. It doesn't really matter in the context of > > WAL recovery, since there can't be any concurrent access to the buffer, > > but it'd make it safe to use in non-WAL contexts (I think there are > > other places where we know we are going to init the page and so a > > physical read is a waste of time). > > To implement that correctly, I think we'd need to take the content lock > to clear the buffer if it's already found in the cache. It doesn't seem > right to me for the buffer manager to do that, in the worst case it > could lead to deadlocks if that function was ever used while holding > another buffer locked. > > What we could have is the semantics of "Return a buffer, with either > correct contents or completely zeroed out". It would act just like > ReadBuffer if the buffer was already in memory, and zero out the page > otherwise. That's a bit strange semantics to have, but is simple to > implement and works for the use-cases we've been talking about. > > Patch implementing that attached. I named the function "ReadOrZeroBuffer". > > -- > Heikki Linnakangas > EnterpriseDB http://www.enterprisedb.com > > ---------------------------(end of broadcast)--------------------------- > TIP 6: explain analyze is your friend -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
