Kbase 10778: Reading the After Image .ai File? 6.2, 6.3, V7 differences
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
5/10/1998 |
|
Reading the After Image .ai File? 6.2, 6.3, V7 differences
WHEN DO WE READ THE AI FILE ?
V6.3 and V7 are different than V6. V6 reads the ai file during
database warm start. Just as warm start verifies that the
changes logged in the bi file were actually made to the database
it must also verify that the notes actually got to the ai file.
The ai file is read while logging notes. Like the database and
bi files the ai file is extended 16 blocks or more at a time.
So whenever an ai block becomes full it is written out and the
next empty block is read in. This read is obviously not necessary.
It is done, however, to make io on the ai file completely consistent
with the database and bi files, thus simplifying the block manager
subsystem. Also keep in mind that this read, in Unix anyway,
should not be expensive since Unix performs read ahead which means
that most of the time the block read is already in the Unix buffer
pool. As part of the 6.3 performance enhancements this read while
logging was done away with. The ai io subsystem had to be rewritten
anyway for V6.3 to support multiple ai buffers as well as support
an asynchronous ai buffer writer.
Progress Software Technical Support Note # 10778