seqdetect - Sequential detection and readahead flag configuration parameter

This parameter controls whether the database manager is allowed to perform sequential detection or readahead prefetching during I/O activity.

Configuration type
Parameter type
Configurable online
Propagation class
Default [range]
Yes [Yes; No ]

The database manager can monitor I/O during index scans, and if sequential page reading is occurring the database manager can activate I/O prefetching. This type of sequential prefetch is known as sequential detection. However, at runtime, the prefetching type might switch from sequential detection prefetching to readahead prefetching when it detects that sequential detection prefetching is not working well enough.

If this parameter is set to No, both sequential detection and readahead prefetching are disabled for the INSPECT command with the INDEXDATA option, the RUNSTATS command, and all index scans during query execution. However, for the REORG command with the CLEANUP option for indexes, setting seqdetect to No disables only sequential detection prefetching for indexes.

Recommendation: In most cases, you should use the default value for this parameter. Try turning seqdetect off, only if other tuning efforts were unable to correct serious query performance problems.