Prevent and prepare for assertion failures

You can perform routine administrative tasks that can prevent assertion failures or help prepare for recovering from assertion failures.

To prevent assertion failures on Informix®, perform the following tasks regularly:

Table 1. Preventing assertion failures.

Prevention task	Purpose
Test your applications thoroughly in a realistic environment before releasing your applications into production.	Applications can trigger assertion failures. Make sure that you have allocated enough resources: for example, physical and logical logs and shared memory.
Check and repair the consistency of your data. Run the following oncheck commands to check your system: oncheck -cD: Data pages oncheck -cI: Index pages oncheck -cr: Reserved pages oncheck -ce: Chunk-free list oncheck -cc: System catalogs oncheck -pe: Physical information about chunks	Diagnosing and repairing consistency problems quickly can prevent major problems like data loss and assertion failures.
Upgrade to the latest major and fix pack release.	Assertion failures can be caused by product defects. You can avoid many product defects by upgrading to the most current release.
Update statistics. When you change a table or indexing schema, update statistics to update the dictionary cache. By default, statistics are updated automatically by the Scheduler. You can customize automatic statistics updating for your system.	Queries that use stale statistics can use too many resources and cause assertion failures. Stale statistics can also have a negative affect on query performance. Always update statistics after upgrading.
Monitor and complete in-place alter operations. You can view pending in-place alter operations in the sysadmin:ph_alerttable or the Health Center > Alerts screen in the IBM® OpenAdmin Tool (OAT) for Informix. You can force the completion of in-place alter operations for a specific table by running the following dummy UPDATE statement: UPDATE table_name SET column_one = column_one WHERE 1=1;	Pending in-place alter operations can use too many resources and cause assertion failures. Complete in-place alters before upgrading.

To prepare for assertion failures on Informix, perform the following tasks regularly:

Table 2. Preparing for assertion failures.

Preparation task	Purpose
Back up your data and logical logs. You can use the on-Bar utility or the ontape utility to back up your data and logical logs. The on-Bar utility requires a storage manager.	If data loss occurs, you can recover your data and recent transactions.
Back up your database and storage space schema information. Run the following commands to back up your schema information: dbschema -ss -d database_name > dbschema_ss_database_name.out: Saves the schema information about the specified database in a file. dbschema -c > dbschema_c.out: Saves the commands to reproduce storage spaces, chunks, physical logs, and logical logs in a file.	In a catastrophic failure, you can recreate your system.

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