Greg Stark <[EMAIL PROTECTED]> writes: > At least for all the possible plans of a given query at a specific > point in time the intention is that the cost be proportional to the > execution time.
Why is this relevant? Given a cost X at a given point in time, the system needs to derive an "expected runtime" Y, and compare Y with the actual runtime. I think that producing Y given an arbitrary X involves so many parameters as to be practically impossible for us to compute with any degree of accuracy. > That's a valid point. The ms/cost factor may not be constant over > time. However I think in the normal case this number will tend > towards a fairly consistent value across queries and over time. It might be true in the "normal case", but that doesn't seem very helpful to me: in general, the mapping of plan costs to execution time can vary wildly over time. Spewing "hints" to the log whenever the system's workload changes, a checkpoint occurs, or the system's RAID array hiccups doesn't sound like a useful feature to me. > On further thought the real problem is that these numbers are only > available when running with "explain" on. As shown recently on one > of the lists, the cost of the repeated gettimeofday calls can be > substantial. That sounds more like an implementation detail than the "real problem" to me -- I think this proposed feature has more fundamental issues. -Neil ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])