Using Parallel Serial Scans

When you need to sequentially read a large table, you can improve performance by using a parallel serial scan. The ALLBASE/SQL optimizer uses a parallel serial scan when it is able to prefetch pages from multiple disk drives in parallel. A parallel serial scan is useful only for large tables that must be read sequentially. It is not beneficial for small tables or for tables that are accessed only by an index.

To take advantage of a parallel serial scan, the following conditions must be met:

The DBEFileset containing the table must contain multiple DBEFiles.
The DBEFiles containing the table must be placed on separate disk drives. You can specify the disk drive with the DEVICE clause of the CREATE DBEFILE statement. If the DBEFile has already been created, you can use the SQLUtil MOVEFILE command.
The DBEFiles cannot be pseudo-mapped because the file system's prefetching must not be bypassed.
The DBEFiles must not contain pages from other tables or index pages from the same table. Put other tables in different DBEFilesets. Use separate INDEX and TABLE DBEfiles for the index and data pages of the table.

Using Parallel Serial Scans

Technical documentation

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