On Tue, 2006-06-06 at 16:50 -0400, Tom Lane wrote: > I have a theory about this, and it's not pleasant at all. What I > think is that we have a Heisenberg problem here: the act of invoking > gettimeofday() actually changes what is measured.
> If this theory is correct, then the entire notion of EXPLAIN ANALYZE > sampling has just crashed and burned. We can't ship a measurement > tool that is accurate on some platforms and not others. Regrettably, I would agree and so conclude that we shouldn't pursue the sampling idea further. Heisenbugs suck time like no other. Interesting, though. That leaves us with a number of possibilities: 0. Do Nothing 1. Option to skip timing altogether on an EXPLAIN ANALYZE 2. Option to produce a partial execution only, to locate problem areas. Any others? Option 2 would be harder to interpret, but still useful - originally discussed in a current thread on -perform. Option 1 wouldn't be as useful as the original sampling idea, but if its not on the table any longer.... I'd revert back to Option 1 as being the best choice for further work. Do we agree the idea can't go further? What next? -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
