Peter Geoghegan <p...@heroku.com> writes: > On Thu, Feb 18, 2016 at 4:15 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> Because they've been removed from the right-link/left-link chains.
> That isn't the same thing as being inaccessible by scans, clearly > (just what you call the "leaf scan sequence"). 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. > 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. regards, tom lane -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers