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User Guide
OpenEdge Replication and after-imaging : The role of after-image extents in the Replication process : After-image extent types
 

After-image extent types

The two types of after-image extents are fixed-length and variable-length. As a general rule, fixed-length extents are preferable to variable-length extents. There are, however, 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 the following table.
Table 1. After-image extent types: benefits and drawbacks
Type
Benefit
Drawback
Fixed-length
Performance asset — 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. You must account for this possibility in after-image planning and implementation.
Variable-length
Performance loss — When a new after-image block is required and there are no empty blocks, the database broker must 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 can involve working with very large files, since the extents can grow to any size. Take into account the possibility that you may need to back up or move these large files.