onstat -g seg Memory Segment Statistics

The onstat -g seg command displays a list of the shared memory segments that have been acquired for this OnLine instance.

Segment Summary:                                                             
id       key        addr     size       ovhd     class blkused  blkfree      
1401     1381451777 a000000  167772160  7504     R*    40376    584          
1302     1381451778 14000000 130023424  4560     V     9341     22403        
1303     1381451779 1bc00000 1048576    624      M     29       227          
Total:   -          -        298844160  -        -     49746    23214        

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

Heading	Description	Format
id	The shared memory identifier returned from the call to shmget() for acquiring shared memory segments.	Dec
key	The key passed to shmget(), based on the value of SERVERNUM.	Dec
addr	The in-memory address of the shared memory segment.	Hex
size	The size of the shared memory segment in bytes.	Dec
ovhd	The number of bytes of overhead within this segment required to track information.	Dec
class	The segment type for this block of shared memory. R Resident V Virtual VX Virtual Extended M Message B Extendable Buffer </div>	Str
blkused	The number of (2 * pagesize in K) K blocks in the segment that have been used.	Dec
blkfree	The number of (2 * pagesize in K) K blocks remaining in the segment.	Dec
Virtual segment low memory reserve (bytes)	The size of reserved memory for use when critical activities are needed and the server has limited free memory	Dec
Low memory reserve used 0 times and used maximum block size 0 bytes)	The number times that the server has used the reserved memory and the maximum memory needed	Int

Notes

Some systems will display multiple R classes. This represents one portion for the buffer pool and one portion for the remainder of the resident segment.

Since V12 the engine can expand the buffer pools if required, these have a class of B

Monitoring and Tuning

If a large number of virtual segments (class 'V') are created under normal load, the SHMVIRTSIZE configuration parameter should be tuned to a higher value.