Snapshot monitor self-describing data stream

After you capture a snapshot with the db2GetSnapshot API, the API returns the snapshot output as a self-describing data stream. Self-describing data includes data attributes such as element names and sizes.

Figure 1 shows the structure of the data stream and Table 1 provides some examples of the logical data groups and monitor elements that might be returned.
Note: Descriptive names are used for the identifiers in the examples and tables. These names are prefixed by SQLM_ELM_ in the actual data stream. For example, collected would appear as SQLM_ELM_COLLECTED in the snapshot monitor output. Types are prefixed with SQLM_TYPE_ in the actual data stream. For example, headers appear as SQLM_TYPE_HEADER in the data stream.
Figure 1. Snapshot Monitor Data Stream
Snapshot monitor self-describing data stream
  1. Each logical data group begins with a header that indicates its size and name. This size does not include the volume of data taken up by the header itself.
  2. Size in the collected header returns the total size of the snapshot.
  3. The size element in other headers indicates the size of all the data in that logical data group, including any subordinate groupings.
  4. Monitor element information follows its logical data group header and is also self-describing.
Table 1. Sample Snapshot Data Stream
Logical Data Group Data Stream Description
collected
1000
header
collected
Size of snapshot data (in bytes).
Indicates the start of a logical data group.
Name of the logical data group.
4
u32bit
server_db2_type
sqlf_nt_server
Size of the data stored in this monitor element.
Monitor element type - unsigned 32 bit numeric.
The name of the monitor element collected.
The collected value for this element.
2
u16bit
node_number
3
Size of the data stored in this monitor element.
Monitor element type - unsigned 16 bit numeric.
The name of the monitor element collected.
The collected value for this element.
db2
200
header
db2
Size of the DB2® level portion of data in the snapshot.
Indicates the start of a logical data group.
Name of the logical data group.
4
u32bit
sort_heap_allocated
16
Size of the data stored in this monitor element.
Monitor element type - unsigned 32 bit numeric.
The name of the monitor element collected.
The collected value for this element.
4
u32bit
local_cons
3
Size of the data stored in this monitor element.
Monitor element type - unsigned 32 bit numeric.
The name of the monitor element collected.
The collected value for this element.
. . .
. . .
appl
100
header
appl
Size of the appl element data in the snapshot.
Indicates the start of a logical data group.
Name of the logical data group.
4
u32bit
locks_held
3
Size of the data stored in this monitor element.
Monitor element type - unsigned 32 bit numeric.
The name of the monitor element collected.
The collected value for this element.
. . .
. . .
agent
50
header
agent
Size of the agent portion of the appl structure.
Indicates the start of a logical data group.
Name of the logical data group.
4
u32bit
agent_pid
12
Size of the data stored in this monitor element.
Monitor element type - 32 bit numeric.
The name of the monitor element collected.
The collected value for this element.
. . .
. . .

The db2GetSnapshot() routine returns the self-describing snapshot data in the user-supplied buffer. Data is returned in the logical data groupings associated with the type of snapshot being captured.

Each item returned by a snapshot request contains fields that specify its size and type. The size can be used to parse through the returned data. A field's size can also be used to skip over a logical data group. For example, to skip over the DB2 record you need to determine the number of bytes in the data stream. Use the following formula to calculate the number of bytes to skip: 
  size of the db2 logical data grouping + sizeof(sqlm_header_info)