On Sat, Oct 20, 2007 at 09:24:07AM +0530, Gokulakannan Somasundaram wrote: > Hi, > I think i have a initial Implementation. It has some bugs and i am working > on fixing it. But to show the advantages, I want to show the number of > Logical I/Os on the screen. In order to show that, i tried enabling the > log_statement option in PostgreSQL.conf. But it shows only the physical > reads. What i wanted was a Logical reads count( No. of ReadBuffer calls, > which is stored in ReadBufferCount variable). So i have added this stats to > the bufmgr.c(function is BufferUsage, i suppose) to show Logical Reads and > Physical Reads. Is this a acceptable change?
I'm not sure if the number of logical reads is really a useful measurement. I can imagine there are places that deliberatly read the block "logically" a few times but drop the pin in between to allow others access. This will skew your results as in actual usage only the first is likely to generate a real I/O. If your problem is cache it seems to me you should test with a table larger than your shared buffers and perhaps even larger than your total memory, since this is the case we're actually interested in. Have a ncie day, -- Martijn van Oosterhout <[EMAIL PROTECTED]> http://svana.org/kleptog/ > From each according to his ability. To each according to his ability to > litigate.
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