Re: PREPARE and GUC plan_cache_mode

Bruce Momjian <bruce@momjian.us> writes:
> Our current docs have this text for PREPARE:
>        Prepared statements can use generic plans rather than re-planning
>        with each set of supplied EXECUTE values. This occurs immediately
>        for prepared statements with no parameters; otherwise it occurs
>        only after five or more executions produce plans whose estimated
>        cost average (including planning overhead) is more expensive than
>        the generic plan cost estimate. Once a generic plan is chosen, it
>        is used for the remaining lifetime of the prepared statement. Using
>        EXECUTE values which are rare in columns with many duplicates can
>        generate custom plans that are so much cheaper than the generic
>        plan, even after adding planning overhead, that the generic plan
>        might never be used.

> There is no mention that PG 12's plan_cache_mode can modify this
> behavior.  I think this needs a doc patch.

Yeah, agreed.  I can do it, or do you want to?

            regards, tom lane