This is a normal feature of the O/S not Unidata. Both Unix and Windows attempt to load files into memory based on last use. Making it VERY hard to test file access methods......!
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Jeffrey Butera Sent: Monday, September 24, 2007 05:34 To: [email protected] Subject: [U2] Internal Cache in Unidata Can anyone speak factually about internal cache in Unidata? In short... I often look at performance and attempt to improve things by changing queries, using indicies, rewriting source and so on. In doing so I perform timing and consistently note that the second time a query is performed, it executes considerably faster than the first. As an example, here's the first execution of a series of queries: SELECT H08.CR.DIV.DATA WITH XCDD.HAMP.CMTE.MEMBER="0202736" time=18ms SELECT H08.CR.DIV.DATA WITH XCDD.DIV EQ "D2" time=988ms SELECT H08.CR.DIV.DATA WITH XCDD.REV EQ "P" time=5ms And then immediately peforming these again: SELECT H08.CR.DIV.DATA WITH XCDD.HAMP.CMTE.MEMBER="0202736" time=18ms SELECT H08.CR.DIV.DATA WITH XCDD.DIV EQ "D2" time=9ms SELECT H08.CR.DIV.DATA WITH XCDD.REV EQ "P" time=5ms To be clear - the difference between 988ms and 9ms is not a typo, it's real. Likewise this is not the result of server load. I can consistently reproduce the above scenario with different queries at different times of the day (and wee hours of the morning with few users). I'm not complaining - it's a perfectly good feature - it's just hard to get accurate timings on things so I often perform queries numerous times and dump the first few executions. Of course, this isn't reality as many queries only get executed once in a blue moon... -- Jeff Butera, Ph.D. Administrative Systems Hampshire College [EMAIL PROTECTED] 413-559-5556 "But Mom - Daddy knows everything." Catherine Butera ------- u2-users mailing list [email protected] To unsubscribe please visit http://listserver.u2ug.org/ ------- u2-users mailing list [email protected] To unsubscribe please visit http://listserver.u2ug.org/
