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SQL programmingYou can use the HCL Informix® implementation of the SQL language to develop applications for Informix® database servers.
Guide to SQL: TutorialThe Informix® Guide to SQL: Tutorial shows how to use basic and advanced structured query language (SQL) to access and manipulate the data in your databases. It discusses the data manipulation language (DML) statements as well as triggers and stored procedure language (SPL) routines, which DML statements often use.
Programming for a multiuser environment
How locks workInformix® database servers support a complex, flexible set of locking features that the topics in this section describe.
Lock scope
Page locks

Page locks

The database server stores data in units called disk pages. A disk page contains one or more rows. In some cases, it is better to lock a disk page than to lock individual rows on it. For example, with operations that require changing a large number of rows, you might choose page-level locking because row-level locking (one lock per row) might not be cost effective.

If you do not specify a LOCK MODE clause when you create a table, the default behavior for the database server is page-level locking. With page locking, the database server locks the entire page that contains the row. If you update several rows that are stored on the same page, the database server uses only one lock for the page.

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