Database isolation levels affect the degree of concurrency among processes that attempt to access the same rows at the same time. There are four levels of isolation:
Use the SQL statement SET ISOLATION to set the isolation level for your session.
If you specify the COMMITTED READ isolation level and use an R-tree index to select rows in a table, all the rows returned by the search are guaranteed to be committed. The same query, however, might not read some of the rows that have been deleted, but not yet committed, by another concurrent transaction.
This behavior differs slightly from that of Informix B-tree indexes. IBM Informix: Guide to SQL Syntax provides detailed information on the type of concurrency that each isolation level enforces for B-tree indexes.
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