Monitor blobspaces to determine the available space and whether the blobpage size is optimal.
The onstat -O option displays information about the staging-area blobspace and the Optical Subsystem memory cache. The totals shown in the display accumulate from session to session. The database server resets the totals to 0 only when you execute onstat -z.
For an example of onstat -O output, see information on the onstat utility in the IBM Informix Administrator's Reference.
The first section of the display describes the following system-cache totals information.
Although the size output indicates the amount of memory that is specified in the configuration parameter OPCACHEMAX, the database server does not allocate memory to OPCACHEMAX until necessary. Therefore, the alloc output reflects only the number of 1-kilobyte pieces of the largest simple large object that has been processed. When the values in the alloc and avail output are equal, the cache is empty.
The second section of the display describes the following user-cache totals information.
If you do not set the INFORMIXOPCACHE environment variable, the database server uses the size that you specify in the configuration parameter OPCACHEMAX.
The oncheck -pB command displays statistics that describe the average fullness of blobpages. If you find that the statistics for a significant number of simple large objects show a low percentage of fullness, the database server might benefit from changing the size of the blobpage in the blobspace.
Execute oncheck -pB with either a database name or a table name as a parameter. The following example retrieves storage information for all simple large objects stored in the table sriram.catalog in the stores_demo database:
oncheck -pB stores_demo:sriram.catalog
For detailed information about interpreting the oncheck -pB output, see optimizing blobspace blobpage size in the chapter on table performance considerations in the IBM Informix Dynamic Server Performance Guide.
The oncheck -pe command provides information about blobspace usage:
Figure 55 shows sample oncheck -pe output.
BLOBSpace Usage Report: fstblob Owner: informix Created: 03/01/99
Chunk: 3 /home/server/blob_chunk Size Used Free
4000 304 3696
Disk usage for Chunk 3 Total Pages
------------------------------------------------------
OVERHEAD 8
stores_demo:chrisw.catalog 296
FREE 3696Use oncheck -pT to monitor dbspaces to determine the number of dbspace pages that TEXT and BYTE data use.
This command takes a database name or a table name as a parameter. For each table in the database, or for the specified table, the database server displays a general tblspace report.
Following the general report is a detailed breakdown of page use in the extent, by page type. See the Type column for information on TEXT and BYTE data.
The database server can store more than one simple large object on the same blobpage. Therefore, you can count the number of pages that store TEXT or BYTE data in the tblspace, but you cannot estimate the number of simple large objects in the table.
Figure 56 shows sample output.
TBLSpace Usage Report for mydemo:chrisw.catalog
Type Pages Empty Semi-Full Full Very-Full
---------------- ---------- ---------- ---------- ---------- ----------
Free 7
Bit-Map 1
Index 2
Data (Home) 9
Data (Remainder) 0 0 0 0 0
Tblspace BLOBs 5 0 0 1 4
----------
Total Pages 24
Unused Space Summary
Unused data bytes in Home pages 3564
Unused data bytes in Remainder pages 0
Unused bytes in Tblspace Blob pages 1430
Index Usage Report for index 111_16 on mydemo:chrisw.catalog
Average Average
Level Total No. Keys Free Bytes
----- -------- -------- ----------
1 1 74 1058
----- -------- -------- ----------
Total 1 74 1058
Index Usage Report for index 111_18 on mydemo:chrisw.catalog
Average Average
Level Total No. Keys Free Bytes
----- -------- -------- ----------
1 1 74 984
----- -------- -------- ----------
Total 1 74 984