Jim C. Nasby wrote: > Yeah, my assumption has been that the only way to tell the difference > would be by timing, but I don't know how practical that is. Since > gettime() or whatever EXPLAIN ANALYZE uses is apparently very expensive, > perhaps there's some other alternative. Perhapse the timing info in > getrusage would work for this. Another idea is setting an alarm for a > fairly short period before making the IO request. If the request comes > back before the alarm fires, the data must have been in the OS cache. > > Another thought is that any IO request that goes to disk would most > likely put the process requesting the IO to sleep, but a request being > served out of cache might not do that. Perhaps there's some way to > recognize that. > > Or maybe a better track would be to develop a patch for as many OSes as > possible that would tell the caller if an IO request came out of cache > or not.
Or give up, which seems the most fruitful approach. -- Bruce Momjian http://candle.pha.pa.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
