On Thu, 2007-09-27 at 10:40 -0400, Tom Lane wrote: > And yet there's another trap here: if the parameter you passed in > chanced to be one of the very common values, a plan that was optimized > for a small number of matches would perform terribly. I wonder could we move prepare_threshold onto the server? (from JDBC). When we prepare a statement, we record the current setting of the prepare_threshold parameter into the plan for that statement. Valid settings are -1, 0 or more. If the setting is -1 then we always re-plan the statement. If the setting is 0 then we plan the statement generically. If the setting is > 0 then we plan the statement according to the specific parameter value and then decrement the prepare count, so eventually the executions will hit 0 (above). That would also simplify JDBC and allow the functionality from other clients, as well as from within PLs. We could also force the plan to be -1 when the planning involves something that would force it to be a one-time plan, e.g. constraint exclusion. (So we could then get rid of that parameter). -- Simon Riggs 2ndQuadrant http://www.2ndQuadrant.com ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
