Re: Measuring relation free space

On 11/06/2011 11:55 PM, Mark Kirkwood wrote: <blockquote cite="mid:4EB764D4.8040702@catalyst.net.nz" type="cite"><font
size="-1"><fontface="Helvetica">I am guessing (at this point very much guessing) that pg_freespace map may return its
datafaster, as pageinspect is gonna have to grovel through all the pages for itself (whereas pg_freespacemap relies on
usinginfo from the ... free space map fork).</font></font><br /></blockquote><font size="-1"><font face="Helvetica"><br
/>I started with pageinspect because I wasn't sure if other methods would be as accurate.  For example, I wasn't sure
untiljust before submission that only the free space and size of the relation are needed to get a useful measure here;
atone point I was considering some other things too.  I've ruled them out as unnecessary as far as I can tell, but I
can'tclaim my tests are exhaustive.  Some review confirmation that this measure is useful for other people is one thing
Iwas hoping for feedback on, as one thing to consider in addition to the actual implementation.<br /><br /> If this
measurementis the only one needed, than </font></font><font size="-1"><font face="Helvetica">as I said at the start of
thethread here it might easily be implemented to run just against the free space map instead.  I'm thinking of what's
beensent so far as a UI with matching output it should produce.  If it's possible to get the same numbers faster,
exactlyhow to implement the function under the hood is easy enough to change.  Jaime already has a new version in
developmentthat adds a ring buffer for example.<br /></font></font><br /><pre class="moz-signature" cols="72">-- 
 
Greg Smith   2ndQuadrant US    <a class="moz-txt-link-abbreviated"
href="mailto:greg@2ndQuadrant.com">greg@2ndQuadrant.com</a>  Baltimore, MD
 
PostgreSQL Training, Services, and 24x7 Support  <a class="moz-txt-link-abbreviated"
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