Solving Problems with Memory Allocation on HP-UX (SAP Library - SAP Database Guide: Informix (BC-DB-INF-DBA))

Solving Problems with Memory Allocation on HP-UX

Use

This section tells you how to solve memory allocation problems for the Informix database with the HP-UX operating system. Problems occur when it is impossible to allocate a single large segment at operating system level, but the allocation of many small segments causes the database server to crash. The result is that not enough memory can be allocated.

This problem only occurs with 32-bit operating systems. With 64-bit operating systems, memory allocation problems no longer occur.

Prerequisites

Consider the following when solving this problem:

HP with Informix only functions successfully with as few segments as possible, that is, no more than five. Therefore, the default with the latest releases is to allocate a single shared memory segment for the resident and the first virtual memory portions.

If more memory needs to be allocated than is available in a single operating system segment, distribute the memory sensibly and then perform the allocation immediately after the database start. In this case, the allocation should not be dynamic according to the SHMADD parameter. Instead, allocate the memory segments manually using onmode -a <kybtes> .

Procedure

Analyze the problem:

Check the amount of memory that is regularly required for database operation by entering the following command:

onstat -g seg

You can also find relevant information in the Informix message file.

Check how much memory is being used by each process.
Check operating system limits.

Solve the problem:

Consider measures to reduce the requirement for shared memory. See SAP note 38307.

Make sure that you have installed all necessary patches for the operating system from HP. See SAP note 76862.
Restart the database.

Result

If you carefully plan shared memory allocation, the database server should be able to successfully allocate memory when it starts.