On Mon, Sep 30, 2019 at 12:05:07PM -0400, Tom Lane wrote: > Bruce Momjian <br...@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?
Uh, I am feeling I can't do anything with the tree until Friday because of the PG 12 packaging, right? -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +
