When you allocate text, unitext, 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, unitext, or image data. This text pointer is known as the first text page.
The first text page contains two parts:
The text data page chain, which contains the text and image data and is a double-linked list of text pages
The optional text-node structure, which is used to access the user text data
Once an first text page is allocated for text, unitext, or image data, it is never deallocated. If an update to an existing text, unitext,or image data row results in fewer text pages than are currently allocated for this text, unitext, or image data, Adaptive Server deallocates the extra text pages. If an update to text, unitext, or image data sets the value to NULL, all pages except the first text page are deallocated.
Figure 1-1 shows the relationship between the data row and the text pages.
Figure 1-1: Relationship between the text pointer and data rows
In Figure 1-1, columns c_text and c_image are text and image columns containing the pages at the bottom of the picture.
