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: 0x01 No mirror 0x02 Mirror 0x04 Down/disable mirror chunks 0x08 Newly mirrored 0x10 BLOBSpace 0x20 BLOBSpace on removable media 0x40 BLOBSpace on optical media 0x80 BLOBSpace has been dropped 0x100 BLOBSpace is optical stage blob 0x200 Space is being physically recovered 0x400 Space has been physically recovered 0x800 Space is being logically recovered 0x1000 A table in the DBSpace has been dropped 0x2000 Temp DBSpace 0x4000 BLOBSpace is being archived. 0x8000 Smart BLOBSpace 0x10000 Either physical or logical log changed 0x20000 Dbspace or chunk tables have changed 0x40000 Dbspace or blobspace contains large chunk 0x80000 Chunk in this dbspace has been renamed 0x100000 Temporary 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. 0x200000 Temporary 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. 0x08000000 The dbspace is being defragmented 0x01000000 The dbspace plogspace. 0x01000000 The dbspace is encrypted. 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: D Down L Being logically recovered P Physically recovered, waiting for logical recovery R Being recovered U Not Backed up X Newly mirrored 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: A 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: E The storage space is encrypted.	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.

onstat -d update will generate the blobpage free list

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.