On Feb 8, 2014, at 8:19 AM, Warren Young <war...@etr-usa.com> wrote: > On Feb 7, 2014, at 5:40 PM, Andrey Repin <anrdae...@yandex.ru> wrote: > >> In either case, repeatedly requesting the same record in a short amount of >> time will only test the system level cache. > > If that were true, moving the requested record around in /etc/passwd wouldn’t > cause a 6x spread in test results. That’s O(N) type behavior, whereas a cache > approaches O(1).
A clarification: I agree that /etc/passwd is being cached for the entire test. My 12-line file is a bit over 1K, so it fits easily into a 4K RAM page. Also, I repeated my tests several times, so even the initial disk read is cached. The fact that we see a 6x speed difference depending on where in the file — or RAM page, if you prefer — the target record is tells us that lookups are dominated by parsing time. Parsing overhead shouldn’t exist for SAM or AD. They’re “pre-parsed.” The equivalent overhead in SAM/AD terms is tree and index traversal, which should happen a lot faster than O(N). -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
