onstat -g nbm Block Map for Non-Resident Segments
The onstat -g nbm command displays the block map for the non-resident (virtual) shared memory segments. A separate block bitmap will be displayed for each segment in shared memory.
Block bitmap for virtual segment address 0x3d394c000:
address = 0x3d394c640, size(bits) = 128000
used = 43146, largest_free = 32870
0:ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
256:ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
512:ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
768:ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
1024:ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
</div>
Output Description
| Heading | Description | Format |
|---|---|---|
| bitmap | In-memory starting address of the used/free blocks in the segment | Hex |
| bitmap size | The number of bytes in the block bitmap | Dec |
| address/data | Starting address followed by 32 bytes of data | Hex/Hex |
| used | The total number of bits in the bitmap that are set to 1 | Dec |
| largest_free | If this is a value other than -1 it is the largest number of consecutive bits that are free | Dec |
Notes
Each bit (1:Used 0:free) of the bitmap represents a 4K block.
Multiply used/largest_free by 4K to get total memory used
If the largest_free has not been calculated then largest_free space will be -1. The largest_free space is maintained on a per memory request basis, it is only calculated when the instance tries to allocate a set of blocks starting at the lastalloc block but there is not enough free space. It is reset to -1 as soon as another block is allocated in the segment.
Multiply used/largest_free by 4K to get total memory used
If the largest_free has not been calculated then largest_free space will be -1. The largest_free space is maintained on a per memory request basis, it is only calculated when the instance tries to allocate a set of blocks starting at the lastalloc block but there is not enough free space. It is reset to -1 as soon as another block is allocated in the segment.