Optionally update statistics on your tables after migrating

Optionally run UPDATE STATISTICS on your tables and on UDRs that perform queries, if you have performance problems after migrating to the new version of Informix®.

An unqualified UPDATE STATISTICS statement includes no additional clauses: 
UPDATE STATISTICS;

By default, an unqualified UPDATE STATISTICS statement updates the statistics in LOW mode for every permanent table in the database, including the system catalog tables.

You can run an UPDATE STATISTICS statement that includes only a FOR ROUTINE clause that specifies no routine name: 

UPDATE STATISTICS FOR ROUTINE;

Running this statement reoptimizes the DML statement execution plans for every SPL routine in the database that operates on local tables.

Similarly, you can substitute the keyword FUNCTION for ROUTINE in the previous example to reoptimize execution plans only for SPL routines that return at least one value, or you can substitute the keyword FUNCTION for PROCEDURE to reoptimize execution plans only for SPL routines that return no value. In these cases, the database server does not update the statistics in the system catalog tables.

You do not need to run UPDATE STATISTICS statements on C or Java™ UDRs.