Tom Lane escribió: > Crash safety. The basic process in vacuum full is: > > * detect that there is room in a lower-numbered page to move the > physically last tuple to. > > * put a copy of the last tuple there. Mark the last tuple itself > as deleted by the VACUUM. Hmm, I've seen people doing piecemeal table shrinking with no exclusive locking by looking up the live tuples in the last page, doing no-op UPDATEs until they moves those tuples to an earlier page with free space, and then hoping that plain VACUUM will detect that this page is empty and truncating it. I wonder if we could write some (semi-) automatic way of doing this. The benefit is that the page ends up truncated to a reasonable of pages, reducing bloat, without requiring the table to be exclusive-locked. The main problem with this approach is that it is fairly painful to deal with CTID values. The operator support for them is pretty poor. -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support
