Craig Ringer <craig@xxxxxxxxxxxxxxxxxxxxx> writes: > Tom Lane wrote: >> This is not correct; PG *never* overwrites an existing record (at least >> not in any user-accessible code paths). > That's what I always thought, but I encountered some odd behaviour while > trying to generate table bloat that made me think otherwise. I generated > a large table full of dummy data then repeatedly UPDATEd it. To my > surprise, though, it never grew beyond the size it had at creation time > ... if the transaction running the UPDATE was the only one active. > If there were other transactions active too, the table grew as I'd expect. > Is there another explanation for this that I've missed? In 8.3 that's not unexpected: once you have two entries in a HOT chain then a later update can reclaim the dead one and re-use its space. (HOT can do that without any intervening VACUUM because only within-page changes are needed.) However, that only works when the older one is in fact dead to all observers; otherwise it has to be kept around, so the update chain grows. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
