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  1. #1
    Join Date
    Feb 2004
    Posts
    26

    Unanswered: Oracle and Sybase memory usage

    We are converting from Sybase to Oracle for a certain application in our business. We currently run 6 Sybase databases on one Sybase instance. We have 4GB of memory dedicated to the one instance for all 6 databases to share in Sybase. We had a meeting with our apps folks to discuss how we were wanting to do the conversion. The vendor app that we use says that we can't use schemas in Oracle.... we have to create 6 individual Oracle database instances. One of our Oracle DBAs was suggesting 6 GB of memory for each database. Of course, they could not understand why Oracle takes 6GB of memory for each of the 6 databases and Sybase only had 4GB of memory dedicated for all 6 databases to share.

    Since I don't know much about Oracle or how it manages memory.... does that sound kind of out of whack to you? Does Oracle actually use that much more memory? Any insight you could give would be appreciated.

    DB
    Dogboy

  2. #2
    Join Date
    Feb 2002
    Location
    Willy is on vacation
    Posts
    1,208
    Not really! It is perfectly normal for a single Oracle instance to consume more resources as compared to Sybase.

    The SGA +PGA takes the bulk of your memory and repeats for each instance unlike Sybase where all databases in a single instance use a common cache, so when you have 4 separate instances, this becomes enormous. I wouldn't think of 4 instances running on the same box, this can grind it down to a halt.

  3. #3
    Join Date
    Feb 2007
    Posts
    71
    Quote Originally Posted by dogboy11
    Since I don't know much about Oracle or how it manages memory.... does that sound kind of out of whack to you? Does Oracle actually use that much more memory? Any insight you could give would be appreciated.

    DB
    Providing a big memory for Oracle gives it a boost in performance. It would really help you understand if you read a couple of articles governing Oracle Memory structures and processes

    For me, after creating the database, I'd start out with identifiying reference tables and transactional tables so that I could create corresponding tablespaces for them.

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