On Mar 26, 2011, at 4:16 PM, Jan Wieck <JanWieck@Yahoo.com> wrote:
> That was what I meant. Go in steps of 16-64MB backwards and scan from there to the current end in forward direction
tofind a nondeletable block. In between these steps, release and reacquire the exclusive lock so that client
transactionscan get their work done.
Well, VACUUM uses a 16MB ring buffer, so anything that size or smaller should hit shared_buffers most of the time.
I wonder though if this might defeat read-behind on operating systems that do have a working implementation. With our
currentapproach each read will end at the point the previous read started, which might be an algorithm somebody is
usingto detect a backward scan.
...Robert
