You switch to a new AI extent for the following reasons:

  • As part of the backup schedule
  • When the current fixed-length AI extent is full, or when the disk holding the current variable-length AI extent is full
  • Before archiving an AI extent

Except when you switch to a new extent because the current extent is full, switching to a new AI extent establishes a starting point for backup; after you restore the backup, you roll forward starting from that extent.

Note: When you perform an online backup, PROBKUP automatically switches over to a new extent as long as the next extent is empty. Before you perform the online backup, make sure that the next extent is empty.

A fixed-length extent has a predefined size, so the database engine can determine when the extent becomes full.

When you switch the AI file, a message writes the number of bytes used in the file to the .db log file, as follows:
[2022/07/22@01:35:50.500-0400] P-19840      T-19840 I ABL     2: (20610) 16375779 bytes(15992 KB) used in after-image extent /scratch/lopez/126/test.a4.

The amount of the data in an AI file reflects Create, Update, and Delete (CUD) operations that happened while the AI file was used.

In contrast to a fixed-length extent, a variable-length extent does not have a predefined maximum size. Therefore, the database engine cannot anticipate when the extent is about to become full. Unless you force a switch using RFUTIL AIMAGE NEW, the database engine continues writing to the extent until an operating system limitation is reached, you reach the 2GB addressable AI file limit without large files enabled, or there is no more room left on the disk. When the extent becomes full, the database engine automatically switches to the next extent, provided that the next extent is empty. For more information on large files, see Database creation and large file support.

If the next extent is full, the database engine shuts down the database. However, you can use the After-image Stall (-aistall) parameter to suspend database activity and send a message to the log file or you can use the RFUTIL qualifier AIMAGE AIOFF to disable after-imaging. If you use -aistall, you can archive the oldest full extent and mark it as empty. The system will then automatically switch to that extent and resumes database activity automatically. For more information on the -aistall parameter, see Database Startup Parameters. If you use RFUTIL AIMAGE AIOFF, after-imaging becomes disabled and can no longer write notes.

Note: You can only use the -aistall parameter and RFUTIL AIMAGE AIOFF in multi-user mode.

When the database engine suspends database activity or shuts down the database, it sends the following message to the log file:

Can't switch to after-image extent filename it is full.
Backup ai extent and mark it as empty (3774)

The database engine cannot resume database activity until the next extent is backed up and marked as empty.