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.

The oncheck utility provides the following options and information that apply to contiguous space and extents.
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.


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