If you journal access paths, the system can use the journal entries to recover access paths instead of rebuilding them completely.
When your server ends abnormally, perhaps because of a power interruption, the next IPL can take much longer than a normal IPL. Rebuilding access paths contributes to this long IPL time. When you perform an IPL after an abnormal end, the system rebuilds access paths that were exposed, except those access paths that are specified as MAINT(*REBLD) when you create the file. An access path is exposed if changes have been made to it that have not been written to the disk.
If you journal access paths, the system can use the journal entries to recover access paths instead of rebuilding them completely. This reduces the time it takes to IPL after the system ends abnormally. Access path journaling is strictly for the purpose of server recovery during an IPL. You do not use access path journal entries when you are applying journal changes to recover a file.
If certain access paths and their underlying files are critical to your operation, you want to ensure that these files are available as soon as possible after the system ends abnormally. You can choose to journal these access paths. This is called explicit access path journaling.
Explicit access path journaling differs system-managed access-path protection (SMAPP) in that with SMAPP you cannot control which access paths the system chooses to protect. Therefore, if the system does not protect the access path that you consider critical to meet your target recovery times, you must explicitly journal that access path.
If you choose to journal an access path, remember the following:
- You can journal an access path for a physical file only if the physical file has a keyed access path or an index created by a referential constraint.
- Before you start journaling an access path, you must journal all the underlying physical files to the same journal.
- You can journal only access paths that are defined as MAINT(*IMMED) or MAINT(*DLY).
Some access paths with international components for unicode
(ICU) sort sequence tables are too complex to be journaled. You
can journal access paths with other sort sequence tables, and many of the
access paths with ICU sort sequence tables.
The System-managed access-path protection topic has detailed information about SMAPP.