Re: PREPARE and GUC plan_cache_mode

Bruce Momjian <bruce(at)momjian(dot)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