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  1. #1
    Join Date
    Mar 2003

    Unanswered: DB2 Varchar question

    We are running with db2 v8.1 Z/OS390. We have a table which has couple of integer/ char fields and four varchar fields which are more than 1000. My DBA is saying that it is good to move big varchar's ( more than two varchar's which are more than 1000 char) to a new table which will improve performance.
    Any simple reason why?. As the DBA is my client I can not ask this question to him.
    Any ideas.

  2. #2
    Join Date
    May 2003
    If you will updating the varchar columns, then it might be better to move them. There are two concerns here: whether they will fit back on the same page if the data is nade larger because of an update, and the issue of logging the changes from the point of column that was changed to the end of the row.

    Also, the more rows you can fit on a page at one time, usually this is best for perfomance. If the large varchar columns are in the same table with the other data, this will either reduce the number of rows per page, or require a larger page size. Larger page sizes have buffer pool implications. But it really depends on how often the large varchar columns are accessed compared to the other columns on the row. If they are always accessed together, then it may be better to leave them together on the same table.
    M. A. Feldman
    IBM Certified DBA on DB2 for Linux, UNIX, and Windows
    IBM Certified DBA on DB2 for z/OS and OS/390

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