Database failures

IMS issues message DFS0451I or DFS0451A when there is an error in an IMS database. Every time IMS encounters a DL/I I/O error, IMS creates an extended error queue element (EEQE) that identifies the block or VSAM control interval in error.

When IMS closes a database, it automatically retries read and write errors on DL/I databases. If successful, forward recovery of the database is not required. Otherwise, forward recovery is eventually required. It might be possible to defer recovery to a more convenient time. Deferring recovery does not inhibit scheduling access or updating.

Using DEDB multiple area data sets also allows application programs to continue when I/O errors exist. For DEDB I/O errors, IMS issues messages DFS2571, DFS2572, DFS3712, and DFS3713. If a DEDB area is not available, the application receives an FH status code.

IMS maintains I/O information and buffer images across restarts. IMS does this by recording the EEQEs in DBRC, notifying all systems that are using the IRLM, and, during initialization and checkpoint, logging EEQEs and virtual buffers to the OLDS.