Setting the collection read mode (transaction isolation level)

You can specify whether form queries read committed or uncommitted data by setting the Collection Read Mode process default. This setting applies to queries that load primary collections, secondary collections, and lists, and to in-collection validations. It also applies to background-task queries that generate reports and to background-task stored procedures. The setting does not affect SQL SELECT operations or other processing coded in stored procedure (method) calls. The default Collection Read Mode value, UNCOMMITTED, corresponds to the Transact-SQL statement

SET TRANSACTION ISOLATION LEVEL READ
        UNCOMMITTED

With the UNCOMMITTED setting, which allows the reading of uncommitted data, users do not have to wait for other long-running transactions that access the same dataset to complete before their queries can complete.

With the COMMITTED setting, a query reads committed data and returns only data for which the query can get a shared lock.

This base, system-wide transaction isolation level (Collection Read Mode) is set on the Process Defaults form. Note that if this setting is unsuitable for all forms and tasks, you can override it for selected forms and tasks. You can set the isolation level for individual reports and stored procedures on the Background Task Definitions form. You can also override the system setting at the form level in the designer (Web Designer in the web client, Design Mode in the Windows client). for information about setting the read mode for a collection and about setting transaction isolation levels, see About transaction isolation levels.