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Process documentation Extension of a Dbspace  Locate the document in its SAP Library structure

Purpose

This section describes the extension of a dbspace in an Informix database. It is important to extend a dbspace in good time, otherwise the availability of your SAP System might be affected.

To extend a dbspace, SAPDBA adds a new chunk to the dbspace, or you do this manually. Before you add the chunk, you have to decide how large to make it and where to put it.

Prerequisites

You need to extend a dbspace in any of the following situations:

Recommendation

SAP recommends you to use the alert monitor to help prevent dbspaces running out of space. The alert monitor automatically warns you of problems.

Process Flow

  1. You decide on the size of the dbspace extension, using the following guidelines:

    2. · Make the new chunk large enough to accommodate medium to long term dbspace growth. This reduces the chance of an error occurring again soon.

    · For a critical, rapidly growing dbspace, you make the chunk as large as possible.

    · You take account of the available storage space and the storage requirements of other dbspaces.

    · You do not allocate chunks where the sum of offset plus chunk size is larger than 2 GB if you are extending a dbspace or creating a new one. This leads to severe problems. Refer to SAP Notes 34722 and 28335. SAP recommends you to use SAPDBA to add chunks (see "Results" below), because it prevents the allocation of chunks larger than 2 GB.

    If you allocate raw devices (UNIX) or NTFS files (NT) with a maximum size of 2 GB, as recommended in the installation documentation, you are less likely to make this mistake with chunks.

    · You extend rapidly-growing dbspaces by at least the following amount:

    Minimum Extension Sizes for Rapidly-Growing Dbspaces

    Dbspace

    Minimum Extension Size (in MB) for Dbspace

    PSAPSTAB

    600

    PSAPBTAB

    300

    PSAPCLU

    150

    PSAPPOOL

    400

    PSAPPROT

    200

    During an SAP update or upgrade, you might also have to extend dbspaces. The upgrade tools show you the relevant dbspaces and how much larger you must make them.

  2. When deciding where to locate the dbspace extension, you use Listing Devices with SAPDBA to identify a suitable disk for the new chunk. You need to beware of creating new "hotspots" as described in the following example:

Example

You go into live production with a certain disk capacity. After some time in production, the available disks fill up. Therefore, you buy a large new disk. Now all database extensions go on the new disk. As most application activity is on new data, the new disk becomes a hot spot and performance bottleneck.

When a new disk is added to an existing system, be sure to evenly spread the current data over all available disks (that is, move a certain amount of less active data to the new disk). Therefore, you can locate future dbspace extensions on existing disks rather than concentrate them all on the new disk, if possible. However, if the existing disks are already full, this poses a problem.

One approach to the problem of full disks is to proceed as follows when you install a new disk:
    1. You temporarily remove existing mirror chunks from mirrored dbspaces.

      2. This frees up the disk space that was being used by the mirror chunks.

    2. You distribute your new chunks more evenly (that is, across existing disks rather than all on the new disk).
    3. You move some dbspaces to the new disk, using Reorganization of a Group of Tables or Dbspace with SAPDBA.
    4. You replace the mirror chunks later, distributing them evenly across all disks.

Note

You need to think ahead when planning database growth. The best solution is to install your new disks well before the existing disks becoming full. You can then develop a sensible database expansion strategy that takes account of future requirements and allows balanced growth. This means spreading new dbspace extensions evenly across the available disk drives.

Result

Now that you know the size and location of the new dbspace, you can extend the dbspace in either of the following ways:

 

See also:

Informix documentation at http://www.informix.com