Openserver 6 Data Cache limit - SCO

This is a discussion on Openserver 6 Data Cache limit - SCO ; I'm configuring a new server with Openserver 6 and 16GB of memory. The operating sytem will only configure 3GB of memory for file data cache but I would like to allocate 8GB if possible. I've tried adjusting SEGMAP_BYTES, SEGMAP_PERCENT, SEGKMEM_BYTES, ...

+ Reply to Thread
Results 1 to 5 of 5

Thread: Openserver 6 Data Cache limit

  1. Openserver 6 Data Cache limit

    I'm configuring a new server with Openserver 6 and 16GB of memory.
    The operating sytem will only configure 3GB of memory for file data
    cache but I would like to allocate 8GB if possible.

    I've tried adjusting SEGMAP_BYTES, SEGMAP_PERCENT, SEGKMEM_BYTES,
    SEGKMEM_PERCENT, and UVIRT_EXTENSION. The only one that made a
    difference was UVIRT_EXTENSION and that was mimimal (2MB extra).

    Can anyone tell me if there is a 3GB maximum for file data cache? If
    not, what is the limit and what kernel parameters are involved?

    Thanks.


  2. Re: Openserver 6 Data Cache limit

    On 12 May, 23:14, dni...@supersave.ca wrote:
    > I'm configuring a new server with Openserver 6 and 16GB of memory.
    > The operating sytem will only configure 3GB of memory for file data
    > cache but I would like to allocate 8GB if possible.


    Hi,

    By data cache are you referring to the buffer cache on the server?

    Can you expand on why you think its a good idea to increase the
    value?

    John

    >
    > I've tried adjusting SEGMAP_BYTES, SEGMAP_PERCENT, SEGKMEM_BYTES,
    > SEGKMEM_PERCENT, and UVIRT_EXTENSION. The only one that made a
    > difference was UVIRT_EXTENSION and that was mimimal (2MB extra).
    >
    > Can anyone tell me if there is a 3GB maximum for file data cache? If
    > not, what is the limit and what kernel parameters are involved?
    >
    > Thanks.



  3. Re: Openserver 6 Data Cache limit

    On May 13, 3:24 am, jbol...@sco.com wrote:
    > On 12 May, 23:14, dni...@supersave.ca wrote:
    >
    > > I'm configuring a new server with Openserver 6 and 16GB of memory.
    > > The operating sytem will only configure 3GB of memory for file data
    > > cache but I would like to allocate 8GB if possible.

    >
    > Hi,
    >
    > By data cache are you referring to the buffer cache on the server?
    >
    > Can you expand on why you think its a good idea to increase the
    > value?
    >
    > John
    >



    Hi John

    Yes, I'm referring to the buffer cache. File data cache
    specifically. According to the documentation this cache is now part
    of virtual memory.

    I would like as much file data cache as possible. The system will be
    a database server and I have a few databases totalling about 10GB of
    data. Database access is 99% read and 1% write, so I would like as
    much cached as possible in order to speed queries and reporting.
    Based on our current server, I'll need less that 3GB for user and
    kernel processes, so I would like to allocate as much as I can to
    caching the databases.

    Dan

  4. Re: Openserver 6 Data Cache limit

    On May 13, 2:15 pm, dni...@supersave.ca wrote:
    > On May 13, 3:24 am, jbol...@sco.com wrote:
    >
    > > On 12 May, 23:14, dni...@supersave.ca wrote:

    >
    > > > I'm configuring a new server with Openserver 6 and 16GB of memory.
    > > > The operating sytem will only configure 3GB of memory for file data
    > > > cache but I would like to allocate 8GB if possible.

    >
    > > Hi,

    >
    > > By data cache are you referring to the buffer cache on the server?

    >
    > > Can you expand on why you think its a good idea to increase the
    > > value?

    >
    > > John

    >
    > Hi John
    >
    > Yes, I'm referring to the buffer cache. File data cache
    > specifically. According to the documentation this cache is now part
    > of virtual memory.
    >
    > I would like as much file data cache as possible. The system will be
    > a database server and I have a few databases totalling about 10GB of
    > data. Database access is 99% read and 1% write, so I would like as
    > much cached as possible in order to speed queries and reporting.
    > Based on our current server, I'll need less that 3GB for user and
    > kernel processes, so I would like to allocate as much as I can to
    > caching the databases.
    >
    > Dan


    Hi Dan,

    I am basing these comments on UW7, which is the base of OSR6
    and I am assuming the two operate the same way.

    There is a 3GB limit per process that is inherent in the way user
    virtual
    addresses are assigned. I believe the use of Dynamic Shared Memory
    (DSHM)
    with the correct code and compiler will allow up to 63GB of memory
    to be accessed by a process.

    My guess is that the program(s) you are running are much smaller
    than 3GB so that should not be a problem.

    With UW7 the concept of dedicated memory used for disk cache is
    not valid, the OS will know if a disk block is still in memory and
    "reclaim"
    it rather than access the disk drive. So effectively all memory not
    being used for programs becomes a "disk cache". You will not see
    this in action because the OS releases unused pages but if you
    check with vmstat and see high page reclaim rate and lots of
    free memory it is working correctly.

    A simple test would be to boot the server and run a specific
    database exercise twice. Use sar to record the disk I/O and
    execution times. Shut down the server and remove all but 2GBs
    ( or 4GBs ) of memory and repeat the tests.

    Mike

  5. Re: Openserver 6 Data Cache limit

    On 13 May, 19:15, dni...@supersave.ca wrote:
    > Hi John
    >
    > Yes, I'm referring to the buffer cache. File data cache
    > specifically. According to the documentation this cache is now part
    > of virtual memory.
    >
    > I would like as much file data cache as possible. The system will be
    > a database server and I have a few databases totalling about 10GB of
    > data. Database access is 99% read and 1% write, so I would like as
    > much cached as possible in order to speed queries and reporting.


    Morning Dan,

    Are you sure that your databases are even using the buffer cache?

    Many databases use shared memory to "cache" data and
    some even write directly to disk bypassing the filesystem
    mechanisms of the OS.

    I would recommend that you check your Database doc to see
    how it manages data access and what tunables it recommends
    you tune. I would also suggest that you contact your SCO
    Support provider if you need further advice on this.

    Regards,

    John



+ Reply to Thread