Using the oncheck utility to monitor I/O utilization
Disk I/O operations are usually the longest component of the response time for a query. You can use the oncheck Utility to monitor disk I/O operations.
Contiguously allocated disk space improves sequential disk I/O operations, because the database server can read in larger blocks of data and use the read-ahead feature to reduce the number of I/O operations.
The oncheck utility displays information about storage structures on a disk, including chunks, dbspaces, blobspaces, extents, data rows, system catalog tables, and other options. You can also use oncheck to determine the number of extents that exist within a table and whether or not a table occupies contiguous space.
| Option | Information |
|---|---|
| -pB | Blobspace simple large object (TEXT or BYTE data)
For information about how to use this option to determine the efficiency of blobpage size, see Determine blobpage fullness with oncheck -pB output. |
| -pe | Chunks and extents For information about how to use this option to monitor extents, see Checking for extent interleaving and Eliminating interleaved extents. |
| -pk | Index key values. For information about how to improve the performance of this option, see Improving performance for index checks. |
| -pK | Index keys and row IDs For information about how to improve the performance of this option, see Improving performance for index checks. |
| -pl | Index-leaf key values For information about how to improve the performance of this option, see Improving performance for index checks. |
| -pL | Index-leaf key values and row IDs For information about how to improve the performance of this option, see Improving performance for index checks. |
| -pp | Pages by table or fragment For information about how to use this option to monitor space, see Considering the upper limit on extents. |
| -pP | Pages by chunk For information about how to use this option to monitor extents, see Considering the upper limit on extents. |
| -pr | Root reserved pages For information about how to use this option, see Estimating tables with fixed-length rows. |
| -ps | Space used by smart large objects and metadata in sbspace. |
| -pS | Space used by smart large objects and metadata
in sbspace and storage characteristics For information about how to use this option to monitor space, see Monitoring sbspaces. |
| -pt | Space used by table or fragment For information about how to use this option to monitor space, see Estimating table size. |
| -pT | Space used by table, including indexes For information about how to use this option to monitor space, see Performance of in-place alters for DDL operations. |
For more information about using oncheck to monitor space, see Estimating table size. For more information about concurrency during oncheck execution, see Improving performance for index checks.