Re: Does IMMUTABLE property propagate?

<p>The immutable property had nothing to do with caching results. Postgres never caches the results of functions. The
immutableproperty is used top determine if it's safe to use indexes or other plans that avoid evaluating an expression
repeatedly.<p><blockquotetype="cite">On 6 Mar 2010 02:45, "Petru Ghita" <<a
href="mailto:petrutz@venaver.info">petrutz@venaver.info</a>>wrote:<br /><br />-----BEGIN PGP SIGNED MESSAGE-----<br
/>Hash: SHA1<br /><br /> Given f1(x) as IMMUTABLE and f2(x) as IMMUTABLE, and f3(f1,f2) as<br /> IMMUTABLE, does the
queryplanner cache the result of f3 and reuse it<br /> or if you want to get a little more speed you better explicitly
define<br/> yourself f3 as IMMUTABLE?<br /><br /> I had an aggregate query like:<br /><br /> select id,<br />      
sum(p1*f1(a)/f2(b)as r1,<br />       sum(p2*f1(a)/f2(b) as r2,<br />       ...<br />       sum(pn*f1(a)/f2(b) as rn<br
/><br/> ...<br /> group by id;<br /><br /> Where f1(x) and f2(x) were defined as IMMUTABLE.<br /><br /> By the
experimentsI ran looks like after defining a new function<br /> f3(a,b):= f1(a)/f2(b) and rewriting the query as:<br
/><br/> select id,<br />       sum(p1*f3(a,b) as r1,<br />       sum(p2*f3(a,b) as r2,<br />       ...<br />      
sum(pn*f3(a,b)as rn<br /><br /> ...<br /> group by id;<br /><br /> *Looks like* I got a little (5%) improvement in
performanceof the<br /> query. Is there a way to find out if the function is re-evaluated each<br /> time?<br /> Is
thisthe recommended way to proceed?<br /><br /> Thank you!<br /><br /> Petru Ghita<br /> -----BEGIN PGP
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