Re: HOT pgbench results

Heikki Linnakangas wrote: <blockquote cite="mid:46B8844C.2050506@enterprisedb.com" type="cite"><pre wrap="">Tom Lane
wrote:</pre><blockquote type="cite"><pre wrap="">Heikki Linnakangas <a class="moz-txt-link-rfc2396E"
href="mailto:heikki@enterprisedb.com"><heikki@enterprisedb.com></a>writes:   </pre><blockquote type="cite"><pre
wrap="">HOTgreatly reduces the number of vacuums needed. That's good, that's
 
where the gains in throughput in longer I/O bound runs comes from.     </pre></blockquote><pre wrap="">But surely
failingto auto-analyze after a HOT update is a bad thing.   </pre></blockquote><pre wrap="">
 
Hmm, I suppose. I don't think we've spend any time thinking about how to
factor in HOT updates into the autovacuum and autoanalyze formulas yet.

I'd argue that HOT updates are not as significant as cold ones from
statistics point of view, though, because they don't change indexed
columns. HOT-updated fields are not likely used as primary search quals. </pre></blockquote> Even for fields that are
usedin primary searches, HOT updates avoid changing the disk block layout, and as reading from the disk is usually the
mostexpensive operation, the decisions shouldn't change much before and after a HOT update compared to before and after
aregular update.<br /><br /> Cheers,<br /> mark<br /><br /><pre class="moz-signature" cols="72">-- 
 
Mark Mielke <a class="moz-txt-link-rfc2396E" href="mailto:mark@mielke.cc"><mark@mielke.cc></a>
</pre>