Data structures used for storing text and image data

When you allocate text or image data, a 16-byte text pointer is inserted into the row you allocated. Part of this text pointer refers to a text page number at the head of the text or image data. This text pointer is known as the first text page (FTP).

The FTP contains two parts:

Once an FTP is allocated for text or image data, it is never deallocated. If an update to an existing text or image data row results in fewer text pages than are currently allocated for this text or image data, Adaptive Server deallocates the extra text pages. If an update to text or image data sets the value to NULL, all pages except the FTP are deallocated.

Figure 1-1 shows the relationship between the datarow and the text pages

Figure 1-1: Relationship between the textpointer and datarows

In Figure 1-1, columns c_text and c_image are text and image columns containing the pages at the bottom of the picture.