The following example (see Figure 1), demonstrates how buffers are scheduled for direct access. Assume the following:

• Two strings
• Three-level index structure as shown
• Three data buffers (one for each string, and one for splits)
• Four index buffers (one for highest level of index, one for second level, and one for each string)

Request 1. A control interval from CA2 is requested by string 1.

• The highest level index set, IS1, is read into an index buffer. IS1 remains in this buffer for all requests.
• IS1 points to IS2, that is read into a second index buffer.
• IS2 points to the sequence set, SS2, that is read into an index buffer for string 1.
• SS2 points to a control interval in CA2. This control interval is read into a data buffer for string 1.

Request 2. A control interval from CA3 is requested by string 2.

• IS1 and IS2 remain in their respective buffers.
• SS3 is read into an index buffer for string 2.
• SS3 points to a control interval in CA3. This control interval is read into a data buffer for string 2.

Request 3. The first control interval in CA6 is requested by string 1.

• IS1 remains in its buffer.
• Since IS1 now points to IS3, IS3 is read into the second index buffer, replacing IS2.
• SS6 is read into an index buffer for string 1.
• SS6 points to the first control interval in CA6. This control interval is read into a data buffer for string 1.

Request 4. The first control interval in CA6 is now requested by string 2.

• IS1 and IS3 remain in their respective buffers.
• SS6 is read into an index buffer for string 2.
• SS6 points to the first control interval in CA6. This control interval is read into a data buffer for string 2.
• If the string 1 request for this control interval was a GET for update, the control interval would be held in exclusive control, and string 2 would not be able to access it.

Suggested number of buffers for direct processing:

   Index buffers
      Minimum = STRNO
      Maximum = Number of Index Set Records + STRNO
   Data buffers
      STRNO + 1