Structure of a Regular Dbspace

After disk-space initialization, you can add new dbspaces. When you create a dbspace, you assign at least one chunk (either raw or cooked disk space) to the dbspace. This chunk is referred to as the initial chunk of the dbspace. Figure 2 illustrates the structure of the initial chunk of a regular (nonroot) dbspace.

When the dbspace is first created, it contains the following structures:

• Two reserved pages
• The first chunk free-list page in the chunk
• The tblspace tblspace for this dbspace
• Unused pages
  Figure 2. Initial Chunk of Regular Dbspace

  

Structure of an Additional Dbspace Chunk

You can create a dbspace that contains more than one chunk. The initial chunk in a dbspace contains the tblspace tblspace for the dbspace. Additional chunks do not. When an additional chunk is first created, it contains the following structures:

• Two reserved pages
• The first chunk free-list page
• Unused pages

Figure 3 illustrates the structure of all additional chunks in a dbspace. (The structure also applies to additional chunks in the root dbspace.)

Figure 3. Additional Dbspace Chunk

Structure of a Mirror Chunk

Each mirror chunk must be the same size as its primary chunk. When a mirror chunk is created, the database server writes the contents of the primary chunk to the mirror chunk immediately.

The mirror chunk contains the same control structures as the primary chunk. Mirrors of blobspace, sbspace, or dbspace chunks contain the same physical contents as their primary counterpart after the database server brings them online.

Figure 4 illustrates the mirror-chunk structure as it appears after the chunk is created.

Figure 4. Mirror-Chunk Structure

The mirror-chunk structure always shows no free space because all of its space is reserved for mirroring. For more information, see the chapter on what is mirroring in the IBM Informix Administrator's Guide.