From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | fabio(at)vuole(dot)me |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Unexpected planner behavior with *_pattern_ops index matching |
Date: | 2014-10-30 22:39:06 |
Message-ID: | 11777.1414708746@sss.pgh.pa.us |
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Lists: | pgsql-general |
Fabio Ugo Venchiarutti <fabio(at)vuole(dot)me> writes:
>>> Conversion of the pattern to an index qualification requires that the
>>> pattern be a plan-time constant. STABLE functions, by definition,
>>> are not that.
> I guess it is correct to assume that the same applies to regular
> expressions stored in pl/pgsql variables/arguments then, as they're
> inspected after the plan is cached?
Not necessarily. Recent PG versions will generate custom plans (ie,
plans for the query with parameter values substituted as constants)
if that consistently offers a significant win over the generic plan.
Which it would as long as the parameter value always reduces to a
reasonably long left-anchored pattern.
regards, tom lane
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