Tables

In relational database systems, a table is a row of column headings together with zero or more rows of data values. The row of column headings identifies one or more columns and a data type for each column.

When you create a table, the database server allocates disk space for the table in a block of pages called an extent. (See Extents.) You can specify the size of both the first and any subsequent extents.

You can place the table in a specific dbspace by naming the dbspace when they create the table (usually with the IN dbspace option of CREATE TABLE). When you do not specify the dbspace, the database server places the table in the dbspace where the database resides.

You can also:

• Fragment a table over more than one dbspace. However, you cannot put fragments into different page-size dbspaces. All fragments might need to be the same page size.

  You must define a distribution scheme for the table that specifies which table rows are located in which dbspaces.

• Create multiple partitions of a fragmented table within a single dbspace if the fragmented tables uses an expression-based or round-robin distribution scheme.

A table or table fragment resides completely in the dbspace in which it was created. The database server administrator can use this fact to limit the growth of a table by placing a table in a dbspace and then refusing to add a chunk to the dbspace when it becomes full.

For more information about distribution schemes, see the IBM Informix Database Design and Implementation Guide. For information on how to fragment tables and indexes over multiple disks to improve performance, concurrency, data availability, and backups, refer to your IBM Informix Dynamic Server Performance Guide.

A table, composed of extents, can span multiple chunks, as Figure 47 shows.

Figure 47. Table That Spans More Than One Chunk

Simple large objects reside in blobpages in either the dbspace with the data pages of the table or in a separate blobspace. When you use the Optical Subsystem, you can also store simple large objects in an optical storage subsystem.

For advice on where to store your tables, see Disk-Layout Guidelines and your IBM Informix Dynamic Server Performance Guide.