Kbase 17645: Truncation of the ai file and changing its blocksize
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
5/10/1998 |
|
Truncation of the ai file and changing its blocksize
When adjusting the blocksize and cluster size for bi file it is
important that the blocksize be consistent with that of the ai file.
This is mainly to eliminate the multpile writes of the same bi block
thus a significant performance hit.
The circumstances under which you would want to change the bi and ai
blocksize vary from database to database and will have to be tested on
a particular database to see any net gains or losses.
The syntax for changing the bi blocksize is:
proutil db-name -C truncate bi -biblocksize
The options for block sizes are 0,1,2,4,8, and 16 in kilobytes.
If you have a single volume ai file enabled when you enter this
command then you must use the After-image Filename (-a) parameter to
specify the AI file name.
When increasing the bi blocksize it may also be advantageous to
increase the bi cluster size to reduce i/o overhead and increase the
intervals between checkpoints.Changing the cluster size can also be
achieved during the truncation of the bi file with the following
syntax:
proutil db-name -C truncate bi -bi size [-biblocksize size]
The options for the bi cluster size are the number must be a multiple
of 16 in the range of 16 to 262128(16k-256MB). The default cluster
size is 128K, and clusters that range from 512 to 4096 are the most
beneficial.
NOTE: You can pass both of these parameters with the proutil truncate
bi command.
To stay in line with the first paragraph of this knowledgebase it is
important to change the ai blocksize as well to keep it consistent
with the bi blocksize. This can be achieved during the truncation
of the ai file as follows:
rfutil db-name -C aimage truncate -aiblocksize size
NOTE: If using a single volume ai file, rfutil db-name -C aimage new
will truncate the ai file,mark it empty, and ready it for restart of
the database.
There is not an option to change the ai cluster size because there is
no clustering mechanism inherent to the ai file.Checkpointing and the
reuse of bi blocks and clusters is limited to the bi file only.The
only way to reuse space in the ai file is to use ai new as mentioned
previously or to use the following:
rfutil db-name -C aimage extent empty
Once this is done, Progress overwrites the contents of the file.
There are many different techniques that can be used with after
imaging as far as single vs multivolume files and when or when not to
reuse the files. The strategy you choose depends on your environment,
and before choosing one it is essential to read through Chapter 12 in
the System Administration Guide which is exclusively allocated to
After Imaging.
SDA 2/2/98
Progress Software Technical Support Note # 17645