IT31222: EXCESSIVE MEMORY CAN BE ALLOCATED BEYOND SHMTOTAL WHEN LOW_MEMORY_MGR IS SET

APAR status

• Closed as program error.

Error description

• A database operation that quickly consumed gigabytes of memory
  caused the maximum number of segments to be allocated and ~16GB
  more than SHMTOTAL (~14GB) to be allocated.
  
  While we do not know the exact work executed by the offensive
  session, the memory growth was far too excessive to be deemed
  intentional by the low memory manager.
  
  In this case, the excessive allocation was partially consumed by
  lock allocation and the final segment allocated was quickly
  followed by a lock table overflow assertion as the server could
  not grow the lock table:
  
  Forcing new segment size to 16Mb and non resident.
  Exceeding SHMTOTAL because Low Memory Manager is on.
  Dynamically allocated new virtual shared memory segment (size
  16384KB)
  Memory sizes:resident:71304 KB, virtual:14569956 KB,
  SHMTOTAL:14624874 KB
  
  < this continues for over 1000 segment allocations in only a few
  seconds until...>
  
  Forcing new segment size to 16Mb and non resident.
  Exceeding SHMTOTAL because Low Memory Manager is on.
  Dynamically allocated new virtual shared memory segment (size
  16384KB)
  Memory sizes:resident:71304 KB, virtual:31183332 KB,
  SHMTOTAL:14624874 KB
  
  Error: Number of Informix segments exceeds maximum allowed: 1024
  
  Assert Warning: Lock table overflow - user id 204, session id
  245255
  IBM Informix Dynamic Server Version <version>
                  Who: Session(245255, user@host, 18631,
  0x4bdcc0a8)
                  Thread(379208, sqlexec, 4bd99f08, 8)
                  File: rslock.c Line: 3632
                  Results: Memory allocation error.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * Users of Informix Server prior to 12.10.xC14 and 14.10.xC4.  *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Update to Informix Server 12.10.xC14 or 14.10.xC4 (when      *
  * available).                                                  *
  ****************************************************************
  

Problem conclusion

• Fixed in Informix Server 12.10.xC14 and 14.10.xC4.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  INFORMIX SERVER

• Fixed component ID

  5725A3900

Applicable component levels