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SQL Anywhere 11.0.1 » SQL Anywhere Server - Database Administration » Configuring Your Database » Database options » Introduction to database options » Alphabetical list of options

 

prefetch option [database]

Controls whether rows are fetched to the client side before being made available to the client application.

Allowed values

Off, Conditional, Always

Default

Conditional

Scope

Can be set for an individual connection or for the PUBLIC group. Takes effect immediately.

Remarks

This option controls whether rows are fetched to the client side in advance of being made available to the client application. Fetching several rows at a time, even when the client application requests rows one at a time (for example, when looping over the rows of a cursor) can cut down on response time and improve overall throughput by cutting down the number of requests to the database.

  • Off means no prefetching is done.

  • Conditional (the default) causes prefetching to occur unless the cursor type is SENSITIVE or the query includes a proxy table.

  • Always means prefetching is done even for sensitive cursor types and cursors that involve a proxy table.

The Always value must be used with caution, as it affects some cursor semantics. For example, it causes the sensitive cursor to become asensitive. Old values may be fetched if the value was updated between the prefetch and the application's fetch request. In addition, using prefetch on a cursor that involves a proxy table can cause the error -668, Cursor is restricted to FETCH NEXT operations, if the client attempts to re-fetch prefetch rows. A client may attempt to re-fetch prefetch rows after a rollback or on a fetch relative 0, if a fetch column is re-bound or bound for the first time after the first fetch, or in some cases when GET DATA is used.

The value sensitive cursor types include the ESQL SENSITIVE and SCROLL cursor types, and the ODBC and OLE DB DYNAMIC and KEYSET cursor types.

The setting of the prefetch option is ignored by Open Client and jConnect connections.

If the DisableMultiRowFetch connection parameter is set to YES, the prefetch database option is ignored and no prefetching is done.

This option previously accepted the value On. This value is now an alias for Conditional.

See also