Informix OnLine Dynamic Server Handbook

Correction of physical and logical log behavior description

There are two errors in my description of the functionality of the logical and physical logs. On page 18 I state:

The logical log is used to store the same "before image" of the data but 
it also records what changes were made to the data and whether those changes 
were actually written to disk. 

The first part of that sentence should be rewritten to say 'The logical log stores some "before images" of data . . . ' (my emphasis on 'some' to call out the change). In point of fact, the only "before images" stored in the logical logs are those that accompany an update or delete action.

Continuing with this change, the fourth description on page 317 should be changed to read:

In some cases, "before images" stored in the physical log resulting from update and delete
operations are written into the active logical log -- along with the "after images" 
resulting from insert operations.

Please see page 22-19 of the INFORMIX-OnLine Dynamic Server Administrators Guide for more information. My thanks to the sharp-eyed Informix trainer who caught this. My apologies if I offended you with this error.

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