On Thu, Feb 18, 2016 at 4:53 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Only a physical-order scan, ie vacuum, would visit a dead page > (ignoring transient corner cases like a page getting deleted while an > indexscan is in flight to it). So I think treating it as part of the > fragmentation measure is completely wrong: the point of that measure, > AFAICS, is to model how close an index-order traversal is to linear. > Half-dead pages are also normally very transient --- the only way they > persist is if there's a crash partway through a page deletion. So I think > it's appropriate to assume that future indexscans won't visit those, > either.
Okay. >> there are usage patterns where half-dead pages might accumulate. > > Other than a usage pattern of "randomly SIGKILL backends every few > seconds", I don't see how that would happen. I meant where pages could accumulate without being recycled. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers