IBM® Informix® 12.10

Effect of configuration on I/O activity

The configuration of your database server affects I/O activity.

The following factors affect I/O activity:

The assignment of chunks and dbspaces can create I/O hot spots, or disk partitions with a disproportionate amount of I/O activity.
Your allocation of critical data, sort areas, and areas for temporary files and index builds can place intermittent loads on various disks.
How you configure read-ahead can increase the effectiveness of individual I/O operations.
How you configure the background I/O tasks, such as logging and page cleaning, can affect I/O throughput.

Chunk and dbspace configuration
The number of disks that you use and the configuration of your chunks, dbspaces, and blobspaces affect the performance of your database server. You can improve performance by planning disk use and the configuration of chunks, dbspaces, and blobspaces.
I/O for cooked files for dbspace chunks
On UNIX, you can control the use of direct I/O for cooked files used for dbspace chunks.
Placement of critical data
The disk or disks that contain the system reserved pages, the physical log, and the dbspaces that contain the logical-log files are critical to the operation of the database server. The database server cannot operate if any of these elements becomes unavailable. By default, the database server places all three critical elements in the root dbspace.
Configuration parameters that affect critical data
The configuration parameters that configure the root dbspace and the logical and physical logs affect critical data.
Configure dbspaces for temporary tables and sort files
Applications that use temporary tables or large sort operations require a large amount of temporary space. To improve performance of these applications, use the DBSPACETEMP configuration parameter or the DBSPACETEMP environment variable to designate one or more dbspaces for temporary tables and sort files.
Configure sbspaces for temporary smart large objects
Applications can use temporary smart large objects for text, image, or other user-defined data types that are only required during the life of the user session. These applications do not require logging of the temporary smart large objects. Logging adds I/O activity to the logical log and increases memory utilization.
Placement of simple large objects
You can store simple large objects in either the same dbspace in which the table resides or in a blobspace.
Factors that affect I/O for smart large objects
An sbspace is a logical storage unit, composed of one or more chunks, in which you can store smart large objects (such as BLOB, CLOB, or multi representational data). Disk layout for sbspaces, the settings of certain configuration parameters, and some onspaces utility options affect I/O for smart large objects.
Table I/O
One of the most frequent functions that the database server performs is to bring data and index pages from disk into memory. Pages can be read individually for brief transactions and sequentially for some queries. You can configure the number of pages that the database server brings into memory, and you can configure the timing of I/O requests for sequential scans.
Configuration parameters that affect table I/O
The AUTO_READAHEAD configuration parameter changes the automatic read-ahead mode or disables automatic read-ahead for a query. In addition, the DATASKIP configuration parameter enables or disables data skipping.
Background I/O activities
Background I/O activities do not service SQL requests directly. Many of these activities are essential to maintain database consistency and other aspects of database server operation. However, they create overhead in the CPU and take up I/O bandwidth.

To find the PDF, see Publications for the IBM Informix 12.10 family of products.
For the release notes, documentation notes, and/or machine notes, see the Release Notes page.