- Entry:
- EXPN
- VIT option:
- SMS
- Event:
- Buffer pool expansion
- VIT processing module:
- ISTRACSM
- Control is returned to:
- ISTORAPX
This trace record is generated whenever VTAM® needs to expand a buffer pool. Buffer pool
expansion may occur because of a scheduled request. 
- Byte (hex)
- Contents
- 00–03
- Record ID: C"EXPN"
- 04
- ID is the primary address space ID (ASID). This field is 0 if the ASID is greater than X'FF'.
- 05–07
- 0
- 08–0B
- Address of buffer pool control block (BPCB) for which expansion occurred
- 0C–0F
- Address of pool expansion block (PXB) that is expanded
- 10–13
- Extent address (PXBSTADR)
- 14–15
- Number of pages for an expansion in this pool. Number of pages for an expansion = (BPCBEXLN divided by 4096).
- 16
- Expansion failure code if expansion failed Note: VTAM issues codes 4 through 8 when a failure occurs during a deferred expansion.
- 4
- Not enough CSA storage is available for the expansion.
- 5
- VTAM cannot fix pages in storage because of insufficient page frames or some other page locking problem.
- 7
- Storage unavailable. VTAM’s CSA limit is exceeded.
- 8
- Expansion would cause the pool to exceed its xpanlim specification. See z/OS Communications Server: SNA Network Implementation Guide for additional information about xpanlim.
- 14
- Not enough CSA storage is available for the expansion.
- 15
- VTAM cannot fix pages in storage because of insufficient page frames or some other page locking problem.
- 17
- Storage unavailable. VTAM’s CSA limit is exceeded.
- 18
- Expansion would cause the pool to exceed its xpanlim specification. See z/OS Communications Server: SNA Network Implementation Guide for additional information about xpanlim.
See the explanation of IST154I in z/OS Communications Server: SNA Messages for more information about interpreting byte 16.
- 17
- Flag byte
- Bit
- Meaning
- x... ....
- 1=ISTORFBA caused the expansion.
0=ISTORAPX caused the expansion.
- .x.. ....
- 1=PXB was allocated by this expansion.
0=PXB existed from prior expansion.
- ..x. ....
- 1=Failure to obtain or fix storage.
0=Success in obtaining or fixing storage.
- 18–1B
- Total number of buffers in pool after this expansion (BPCBTOTL)
- 1C–1F
- Total number of available buffers in pool after this expansion