Re: HOT patch - version 15

Tom Lane wrote:
> "Heikki Linnakangas" <heikki@enterprisedb.com> writes:
>> Imagine a page with just one tuple on it:
>
>> 1
>
>> After a bunch of updates, it looks like this
>
>> 1 -> 2 -> 3 -> 4 -> 5
>
>> 1 is the tuple the indexes point to, others are heap only.
>
> But if we were attempting prune at every update, at least some of the
> later updates should have managed to prune.  "2" should certainly be
> gone at this point, unless there's lots of contention for the page,
> in which case pruning at select won't make things better.

Oh I see. Yeah, hopefully you don't end up with long chains too often.
You don't need contention for it, though, a long-running transaction
will cause it. Or a transaction that inserts a tuple and updates it
multiple times in the same transaction.

--
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com