On Thu, 13 Jan 2005, Tzahi Fadida wrote: > I am implementing a new sql operator algorithm called full-disjunction. > I need to experiment with different environment conditions for > it and different cost considerations. > I can estimate the io cost by counting the operations of reading > and writing tuples from the database but it would be very unaccurate. > I am working on postgreSQL and it turns out it only guesstimate the io > cost of a query. Just a few prob: > - postgreSQL is MVCC and thus the tables could be larger than they > actually contain visible tuples. > - the tuples could occupy 4 times their size in the disk. > - what about caching, how does it helps, detters. > - debugging, to see I am not double reading. > and the list goes on... > PostgreSQL can compile In windows where at least on the surface > using the taskmanager related libraries I can access a process > read/write > io. however, I can never know whats with the background writer and it > has probably the same issues as in linux with counting those. > I am better off with linux where I can prove its not doing anything more > than it claims.
you should still define things in a more precise manner (not for us - for your work to be meaningfull). then you should define the manner of measuring things. run it before the changes, run it after the changes, and see the difference. what i've learned from my attempts at performance measurment, is that it is very hard to define the proper experiments that will lead to results that re-create "real life usage" of applications. just some examples: you have cache. you need to decide - should i measure when the cache is empty (i.e. running the test right after a reboot), or after the cache is populated with valid data (i.e. run the test several times, and only then running it once more while emasuring). and cache is just one example - you'll probably have other things too (e.g. running a single transaction at a time or several? how large sohuld the database tables get? large enough to overflow the cache, or small enough to fit into the page cache and thus avoid any real hard-disk access? should i perform the tests several times with different ammounts of RAM? with different CPU types? with different types of storage arrays (which would make a tremendous difference, if your test is I/O bound)... -- guy "For world domination - press 1, or dial 0, and please hold, for the creator." -- nob o. dy ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
