What is the "No reserve memory is allocated" message on 'onstat -g seg'?

Technote (FAQ)


Question

In some Informix instances, 'onstat -g seg' output shows the message "No reserve memory is allocated" near the bottom of the output:

>>% onstat -g seg

IBM Informix Dynamic Server Version 11.70.FC7 -- On-Line -- Up 1 days 03:16:59 -- 175104 Kbytes

Segment Summary:
id key addr size ovhd class blkused blkfree
83886206 52944801 10a000000 119537664 1834184 R 29140 44
83886207 52944802 111200000 33554432 394728 V 8160 32
33554432 52944803 113200000 8388608 99720 V 2046 2
33554433 52944804 113a00000 1048576 13560 M 138 118
33554434 52944805 113b00000 8388608 99720 V 685 1363
33554435 52944806 114300000 8388608 99720 V 25 2023
Total: - - 179306496 - - 40194 3582

 
   (* segment locked in memory)
No reserve memory is allocated
 

Answer

The presence of "No reserve memory is allocated" indicates that the LOW_MEMORY_RESERVE configuration parameter is set to 0.

Use the LOW_MEMORY_RESERVE configuration parameter to reserve a portion of memory which can prevent out of memory errors during critical activities such as rollbacks.

The LOW_MEMORY_RESERVE configuration parameter can be set to a specific amount of memory, in kilobytes, up to 20% of SHMVIRTSIZE. An example output when LOW_MEMORY RESERVE is greater than 0 is demonstrated in this output of 'onstat -g seg':

>>% onstat -g seg

IBM Informix Dynamic Server Version 11.70.FC7 -- On-Line -- Up 1 days 03:16:59 -- 175104 Kbytes

Segment Summary:
id key addr size ovhd class blkused blkfree
83886206 52944801 10a000000 119537664 1834184 R 29140 44
83886207 52944802 111200000 33554432 394728 V 8160 32
33554432 52944803 113200000 8388608 99720 V 2046 2
33554433 52944804 113a00000 1048576 13560 M 138 118
33554434 52944805 113b00000 8388608 99720 V 685 1363
33554435 52944806 114300000 8388608 99720 V 25 2023
Total: - - 179306496 - - 40194 3582

(* segment locked in memory)
Virtual segment low memory reserve (bytes):131072
Low memory reserve used 0 times and used maximum block size 0 bytes

Related information

LOW_MEMORY_RESERVE

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Document information


More support for:

Informix Servers

Software version:

11.7, 12.1

Operating system(s):

AIX, HP-UX, Linux, Solaris, Windows

Reference #:

1662247

Modified date:

2014-06-25

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