Wait type latching

  • CurtM

    SSC-Addicted

    Points: 462

    Anyone have any info on what it means when you see a PAGEIOLATCH_SH in the wait type in Enterprise Manager? I am assuming it means that you are out of memory, since the server it is running on is low on memory, but I wouldn't mind knowing for sure before I tell them they have to buy more RAM.

    Thanks,

    Curt

  • aplack

    SSC Veteran

    Points: 291

    Actually this is a IO bottleneck and not memory. Memory shows up as RESOURCE_SEMEPHORE.

    This is a wait for the IO channel to read a Page from the IO Channel. The Latch is a shared memory key for a specific page of IO (disk) memory. If you have your process ID in the latch memory location, you own the page of IO. If some other process has it's ID, you wait. This is how SQL controls access to physical IO of the system.

    This is NOT the same as a page lock as this would show up as blocking. This WAIT type shows up simply because the IO activity of the computer is busy.

    Faster IO would be better or more disk spindles or faster disk channels (not to exclude a faster/wider bus).

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