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  1. #1
    Join Date
    May 2013
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    25

    Question Unanswered: DB2 HADR memory consumption & network traffic

    Hello people,

    I have two questions and I would be glad if you could provide more information (maybe some stats, graphs or a useful link) because my search lead nowhere.

    First of all, is there somewhere information about the memory consumption of a standby instance? Is it safe to assume that it will consume the same memory as the primary in a high load ebvironment? Or maybe less because actually is a read only db with not so many active connections (only the connections for the replication)?

    Second. How much network traffic does a HADR replication cause? Can we assume again that is double than having only one db2 instance? Or maybe there is a compression mechanism for the log shipping (or something else that I haven't thought of ) ?

    Thank you in advance for your help. If you have any documents that have measurements or have information on the topic it would be great.

  2. #2
    Join Date
    Apr 2006
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    Provided Answers: 11
    in standby you don't have the read/select stmnts from primary
    only d/i/u is replicated
    db2 uses logbuffer shipping whenever commit is executed or threshold reached
    you could define a dedicated network for hadr communications
    Best Regards, Guy Przytula
    Database Software Consultant
    Good DBAs are not formed in a week or a month. They are created little by little, day by day. Protracted and patient effort is needed to develop good DBAs.
    Spoon feeding : To treat (another) in a way that discourages independent thought or action, as by overindulgence.
    DB2 UDB LUW Certified V7-V8-V9-V9.7-V10.1-V10.5 DB Admin - Advanced DBA -Dprop..
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  3. #3
    Join Date
    May 2003
    Location
    USA
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    5,737
    The vast majority of memory required for most databases is for bufferpools, not connections, so it would be the same as the primary server. Also, if you do a HADR takeover to standby, you need the same amount of memory on standby if you want to be able to handle the load.

    As already mentioned, best practice is to set up a private dedicated network (crossover cable is fine) to use for HADR replication traffic.
    M. A. Feldman
    IBM Certified DBA on DB2 for Linux, UNIX, and Windows
    IBM Certified DBA on DB2 for z/OS and OS/390

  4. #4
    Join Date
    Apr 2006
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    Provided Answers: 11
    and a last small remark
    if bp is automatic - the current size in stdby could be smaller as you do not execute the select stmt on stdby and select stmnts could do a table scan and import many pages in bp
    Best Regards, Guy Przytula
    Database Software Consultant
    Good DBAs are not formed in a week or a month. They are created little by little, day by day. Protracted and patient effort is needed to develop good DBAs.
    Spoon feeding : To treat (another) in a way that discourages independent thought or action, as by overindulgence.
    DB2 UDB LUW Certified V7-V8-V9-V9.7-V10.1-V10.5 DB Admin - Advanced DBA -Dprop..
    Information Server Datastage Certified
    http://www.infocura.be

  5. #5
    Join Date
    May 2013
    Posts
    25
    Thank you very much guys. Your information was valuable

  6. #6
    Join Date
    May 2013
    Posts
    25
    Sorry for the double post, but I realised something.

    Isn't the bufferpool space preallocated? I mean, if it is preallocated it doesn't really matter how many pages will be imported in bp...

  7. #7
    Join Date
    Jun 2003
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    Toronto, Canada
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    Provided Answers: 1
    Quote Originally Posted by Haros View Post
    Isn't the bufferpool space preallocated? I mean, if it is preallocated it doesn't really matter how many pages will be imported in bp...
    If the buffer pool size is set to automatic, the STMM might reduce its original size if there is little demand for it while there is demand from other memory consumers.
    ---
    "It does not work" is not a valid problem statement.

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