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What's the index node and index page in DB2

Could you please explain what the index node and index page in DB2, and what's the relationship between them?

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    author's profile photo Former Member
    Former Member
    Posted on Jun 18, 2008 at 02:39 PM

    Hi,

    From your question:

    How to understand index nodes vs index page is 1:1?

    This means that every index node is stored exactly in a page.

    From your explanation I assume your entity relationship diagram is something like this:

    +--------------+              +-----------+
    | Table Record | (n) ---- (1) | Data Page |  
    +--------------+              +-----------+
    
    +------------+              +------------+
    | Index Page | (1) ---- (1) | Index Node |
    +------------+              +------------+
    

    This means, one table record can not be splitted in more than one page. A data page can store many table records.

    And as said before, an index node is stored in an index page.

    Hope this helps

    Best regards, Edgardo

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  • author's profile photo Former Member
    Former Member
    Posted on Jun 18, 2008 at 06:41 AM

    Hi,

    I think, this link provides you with information about the index node concept.

    [http://publib.boulder.ibm.com/infocenter/db2luw/v9/index.jsp?topic=/com.ibm.db2.udb.admin.doc/doc/c0005300.htm]

    To sum up, from my point of view, the "index node" is a more logical concept, because it refers to the different components of the B+ Tree structure used to implement indexes. You have different kinds of index nodes, depending on the level you analyze; for example, the root node, intermediate nodes and leaf nodes. The leaf nodes actually points to the data by means of a RID (row ID).

    On the other hand, the "index page" is a physical concept and it identifies what sort of data is stored on the disk page. A page for DB2 is the smallest unit of storage.

    Hope this helps,

    Best Regards, Edgardo

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    • Former Member

      Following paragraph is copied from tadm56.

      Tables contain records of data. One or more records of a table are stored in a DB2 data page. Pages are the minimum I/O unit of DB2. A DB2 data page can contain one or more records. But a record must fit in a data page.

      If a record of a table does not fit in a 4096 byte (4 KB) page, the table must be defined in a tablespace that is based on a larger page size. DB2 also provides page sizes of 8192 bytes (8 KB), 16384 bytes (16 KB), and 32768 bytes (32 KB).

      For improved access to data, indexes are predefined by SAP developers. Indexes can also be defined later as further need arises. An index is defined using a few columns of a table, which are accessed frequently. Index data structures allow for efficient retrieval of small quantities of data. Indexes are based on nodes, their storage is maintained within DB2 index pages. Because the pointers pointing to other index nodes are also stored in the index pages, storage of indexes is not as compact as the storage of data records.

      And above this paragraph, there is a figure that shows relationship. I don't know how to paste a picture here. In the figure, it shows that table records vs data page is n:1, and index nodes vs index page is 1:1.

      How to understand index nodes vs index page is 1:1?

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