| From: | Florian Pflug <fgp(dot)phlo(dot)org(at)gmail(dot)com> |
|---|---|
| To: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Gregory Stark <stark(at)enterprisedb(dot)com>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org> |
| Subject: | Re: HOT patch - version 15 |
| Date: | 2007-09-08 17:22:20 |
| Message-ID: | 46E2DA4C.3080101@gmail.com |
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| Lists: | pgsql-patches |
Heikki Linnakangas wrote:
> Tom Lane wrote:
>> Compared to what it currently takes to check the same tuple (a separate
>> index entry fetch and traversal to the heap page), this is already an
>> enormous performance improvement.
>
> Though keep in mind that we kill index tuples as soon as they're deemed
> to be dead. Nevertheless, I'm not very worried about the cost of
> following the chain either. But that's something we can quite easily
> measure if we want to.
I'm confused now. I though that pruning would be enough to shorten HOT-Chains -
because the root line pointer afterwards points directly to the first live
tuple. But we can *prune* (without actually defragmenting) without holding
a VACUUM-strength lock, right? Or did I get that wrong?
greetings, Florian Pflug
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