bottleneck in I/O

  • Hi

    if Proflier show ror RPC completed

    CPU 20000

    READ 500000

    Duration 45000

    Does it mean bottlleneck in in amount of I/O that has to be performed for 500000 read operation

    since CPU is only 1/2 of the time of total duration

  • That does not mean that you have a bottleneck in IO. What it would mean is that it is a very expensive query. You will have to take a look at it and fix the query.

    To see bottlenecks you will have to use performance counters and check what is the average queue length etc.

    -Roy

  • To add to what Roy said, and he's right, that just means it's more expensive data wise than it is computationally, there's a few other things you need to see.

    No one number in SQL Server indicates a bottleneck. Some of them do indicate to go look for one, though.

    See the links in my sig, particularly the one for optimization and performance. We'd need to see the .SQLPLANS for this to see why you're read heavy. To find some walkthroughs in taking performance metrics for disk I/O, google up Disk pressure, Disk I/O, Disk Queue, and Physical I/O. Might also lookup PAGEIOLATCH as well, to be able to lookup waitstates.


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  • Yes, that's pretty high for read times.

    Your bottleneck might be poor coding/indexes though, which causes stress on the IO...check the execution plan for that query and try to tune from that side first before you go to the infrastructure.

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