Release 10.1B: Progress Fathom Replication
User Guide


After-image extents

After-image extents contain a series of notes grouped together into after-image blocks. You can use the after-image extents with the roll-forward recovery process to restore the database to the condition it was in before you lost the database, without losing completed transactions that occurred since the last backup.

After-image extent types

There are two types of after-image extents: fixed-length and variable-length. As a general rule, fixed-length extents are preferable to variable-length extents; however, there are circumstances in which variable-length extents may be appropriate. When determining which extent type to use, take into account your business requirements, as well as the benefits and drawbacks of each extent type, as described in Table 2–1.

Table 2–1: After-image extent types 
Type
Benefit
Drawback
Fixed-length
Performance — Fixed extents incur the performance impact for allocating and formatting the blocks at extent creation time. This causes minimal performance impact to the database during normal operations.
Full extent management — It is possible for multiple extents to fill within a cycle of extent management. This must be accounted for in the after-image management.
Variable-length
Performance loss — When a new after-image block is required and there are no empty blocks, the database broker has to allocate and format additional space from the operating system.
Full disks — Extents could grow to take up all of the available disk space.
Larger file management — Management of variable extents could involve very large files since the extents can grow to any size. Backing up of these files or moving them around must be taken into account.

After-image extent states

There are five different after-image extent states that can occur when a database is enabled for Fathom Replication as a source database, as described in Table 2–2.

Table 2–2: After-image extent states 
After-image extent state
Description
EMPTY
The after-image extent is empty and ready to be used by the RDBMS.
BUSY
The after-image extent is currently being written to by the RDBMS. Transaction-log records will accumulate until an extent switch is performed either by the RDBMS when the extent fills or by DBA action when the rfutil db-name -C aimage new command is issued.
LOCKED
The after-image extent is FULL but has not been replicated in its entirety to target database(s). The extent cannot be emptied by the rfutil db-name -C aimage empty command until all transaction-log records have been sent to and applied by the Replication agent. The after-image blocks in an extent in this state can be extracted and written to a new file using the rfutil db-name -C aimage extract command.
FULL

The after-image extent is FULL and is ready to be archived then emptied.

ARCHIVED

The after-image extent has been archived by the After-image Management Utility. For details about the utility, see OpenEdge Data Management: Database Administration .


Copyright © 2006 Progress Software Corporation
www.progress.com
Voice: (781) 280-4000
Fax: (781) 280-4095