onstat -d/-D DBSpaces and Chunks

The onstat -d command provides a two-part output. The first part identifies all known DBSpaces in the instance; the second part identifies the chunks associated with each of the DBSpaces in the first part. The onstat -D command is similar to the output of onstat -d with the exception that the size, free and bpages in the chunk section are replaced by the number of reads and writes that have occurred against the particular chunk.

DBSpace Detail Definitions

Heading Description Format See Also
address The in-memory address of the DBSpace structure. Hex  
number The ordinal number of the DBSpace, assigned in the order the space was created. Dec onstat -D
flags Describes the status of the DBSpace using the following hexadecimal values:
0x01No mirror
0x02Mirror
0x04Down/disable mirror chunks
0x08Newly mirrored
0x10BLOBSpace
0x20BLOBSpace on removable media
0x40BLOBSpace on optical media
0x80BLOBSpace has been dropped
0x100BLOBSpace is optical stage blob
0x200Space is being physically recovered
0x400Space has been physically recovered
0x800Space is being logically recovered
0x1000A table in the DBSpace has been dropped
0x2000Temp DBSpace
0x4000BLOBSpace is being archived.
0x8000Smart BLOBSpace
0x10000Either physical or logical log changed
0x20000Dbspace or chunk tables have changed
0x40000Dbspace or blobspace contains large chunk
0x80000Chunk in this dbspace has been renamed
0x100000Temporary dbspace used by only by shared disk secondary server. It is one of the dbspaces listed in the SDS_TEMPDBS configuration parameter on the SD secondary server.
0x200000Temporary dbspace for the SD secondary server. This is listed in the DBSPACETEMP configuration parameter on the shared disk secondary server.
0x00400000 The dbspace was externally backed up.

The latter flags are not available in earlier engines

Hex  
fchunk The number of the first chunk belonging to this DBSpace. Dec  
nchunks The total number of chunks that make up this DBSpace. Dec  
flags Describes the type of DBSpace using the following coded values: Position 1:
M Mirrored
N Not mirrored
Position 2:
X Newly mirrored
D Down
P Physically recovered, waiting for logical recovery
L Being logically recovered
R Being recovered
Position 3:
B	Blobspace
S	Sbspace
T	Temporary dbspace
U	Temporary sbspace
W	Temporary dbspace on primary server 
	[only shown on SDS servers]
Position 4:
B	DBSpace with chunks larger than 2GB
Position 5:
E	The dbspace is auto-expandable, i.e. 
    SP_AUTOEXPAND is enabled 
    AND 
    (
    the dbspace is configured with a create size 
    OR 
    extend size that is not zero.
    )
Position 6:
D	DirectIO is enabled
Str  
owner The owner of the DBSpace. Str  
name The name of the DBSpace as assigned by the administrator. Str  

Dbspace Summary Definitions

Label Description
active The total number of DBSpaces that have been created for this instance.
total The total number of DBSpaces that OnLine is dynamically configured to manage at this time.

Chunk Detail Definitions

Heading Description Format
address The in-memory address of the chunk structure. Hex
chk The ordinal number of the chunk relative to its creation. Dec
dbs The DBSpace number with which this chunk is associated. Dec
offset The offset (in pages) into the chunk where OnLine will begin writing. Pages
size The size of the chunk in pages. Pages
free The number of unused (free) pages remaining in the chunk. Pages
bpages If this is a BLOB chunk, the approximate number of BLOB pages in use (hence, the tilda). Dec
flags Describes the status of the chunk using the following coded values: Position 1:
P Primary chunk
M Mirror chunk
Position 2:
O OnLine
D Down
I Inconsistent
N Renamed and either Down or Inconsistent
R Recovery
X Newly Mirrored
Position 3:
- Data DBSpace
B BLOB DBSpace
S Smart BLOBSpace
Position 4:
B	DBSpace with chunks larger than 2GB
Position 5:
E	Identifies the chunk as extendable
Position 6:
For cooked file chunks

C	On AIX the concurrent I/O option is enabled
D	The direct I/O option is enabled 

Str
pathname The full pathname of the chunk. Str

Chunk Summary Definitions

Label Description
active The total number of chunks that have been created for this instance.
maximum The maximum number of chunks that this version of OnLine is able to handle.

Chunk I/O Detail Definitions

Column Heading Column Description Format
address The in-memory address of the chunk structure. Hex
chk The ordinal number of the chunk relative to its creation. Dec
dbs The DBSpace number with which this chunk is associated. Dec
offset The offset (in pages) into the chunk where OnLine will begin writing. Pages
page Rd The number of pages read from this chunk since the last boot or onstat -z. Dec
page Wr The number of pages written to this chunk since the last boot or onstat -z. Dec
pathname The full pathname of the chunk. Str

Chunk I/O Summary Definitions

Label Description
active The total number of chunks that have been created for this instance.
maximum The maximum number of chunks that this version of OnLine is able to handle.

Notes

    Fragment elimination and parallelism is performed at the DBSpace level.

    DBSpace numbers and chunk numbers are automatically assigned and are reused if one happens to be dropped.

    When looking for down chunks, it is easiest to 'grep' for the letters 'PD' rather than try to pick 'PD' out of a list of 'PO's, since the two values tend to look very similar.

    There are two types of chunks, primary and mirrored.

    Primary does not refer to the first chunk for a DBSpace; rather, it is a way to refer a chunk that is not the actual mirror.

    Pathnames for chunks should be links to the device file. This will provide for greater flexibility, should a disaster recovery situation occur.

    The initial 53 pages of the first chunk for a DBSpace are used for 2 reserved pages, 1 chunk free list page and 50 pages for the TBLSpace partition.

    The second and follow-on chunks for a DBSpace will initially have an overhead of 3 pages: 2 reserved pages and 1 chunk free list page.

    Different versions of Informix Dynamic Server are designed to handle different maximum numbers of chunks; the current maximum is 32K If a chunk contains the MetaData for a Smart BLOBSpace, the offset listed will indicate: Metadata The onstat -D only displays the page-read and page-write information for the first 50 chunks in each space.

Monitoring and Tuning

    If mirroring is being performed, the primary and mirror chunks should be on different controllers.

    It is important to ensure that your temporary DBSpaces are actually labelled as temporary. You should see a 'T' in the second position of the second flags column of the DBSpace section.