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  1. #1
    Join Date
    Apr 2012

    Unanswered: about showplan I/O message


    Recently my customer's sybase production db has performance problem for some queries, but not in their testing db. I noticed that the I/O messages from the showplan of the same query on the db servers are different.

    from production db server, it is 16kbytes, while on test db server it is 32kbytes, but i found no 32kbytes I/O size from sybases website....

    from sybase website:
    ================Quote from Sybase Site================
    The I/O messages are:

    Using I/O size N Kbtyes for data pages.
    Using I/O size N Kbtyes for index leaf pages.
    These messages report the I/O sizes used in the query. The possible sizes are 2K, 4K, 8K, and 16K.

    I am confused here. Could anyone enlighten me? also want to ask whether the different I/O size could affect the performance of the query greatly.

    thanks in advance,


  2. #2
    Join Date
    Jan 2012
    Hi wayne,

    You are confusing 2 things, one thing is pagesize of the server 2k thats the size of the blocks where the data is written on disk.
    Another thing is cache size, thats memory.
    Check sp_cacheconfig command on sybase.
    Normally for cache you have the global size for example i. your case 2k server and with a cache of 20 mb.
    2k cache - used for some ops. disk init, some dbcc
    16k cache- ( max size 4 times server pgsize) used for other comands like dbcc checkdb

    Regarding the performance if its data cache like this ones, i dont think they have impact on performance since they are used for data, indexes, etc.
    Procedure caches however hace impact, they store statistics, parallel query plans.

    Hope it helps, and if im wrong please correct me.

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