Status: Unverified
GOAL:
How to calculate the size of the After Image file.
FIX:
WHY YOU NEED TO KNOW THIS:
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If you are planning to enable After Image on your Progress version 7 or version 8 Database, you probably want to know how big the After Image file is going to grow so you can allocate enough disk space for it.
In the V7 System Administration Guide on page 12-3 you can see an estimate but this is not accurate enough.
PROCEDURAL APPROACH:
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You can get the closest estimate by monitoring the BI writes for the period you want to use After Imaging before making a backup and starting a new After Image file, normally a working day.
To see how many BI writes have been done, run promon on the database you want the estimate for with the following command:
promon <path + databasename> for example promon /usr/DB/demo
In the main menu type R&D to go to the Research and Development option, then choose menu option 2 and then option 5. Look at the Bytes written line, the Total column, these are the total bytes written to the before image file since start-up of the database.
For example:
10:14:30 10/15/96 23:13 to 10/16/96 10:14 (11 hrs 1 min)
Total Per Min Per Sec Per Tx
Total BI writes 281 0 0.00 1.53
BIW BI writes 136 0 0.00 0.74
Records written 1919 2 0.04 10.48
Bytes written LOOK HERE --> 138488 209 3.48 756.76
Total BI Reads 1573 2 0.03 8.59
Records read 77 0 0.00 0.42
Bytes read 4353 6 0.10 23.78
Since the information which is written in the Before Image file
closely matches what is written in the After Image file, this is a
close estimate of the size of the After Image file. The
difference is about 0.05% (less written in the Before Image file).
Some considerations:
You need to monitor this at the end of the period you are planning to use After Imaging for. You should take several measurements because workloads vary. The size of the bi and ai notes will also vary, depending on the data values in records. There may also be a lot more activity at different times (during end of the month for example). There may be certain types of processing that is not done regularly which would generate a lot more notes, such as if you are deleting last year's history or making occasional mass updates.
When you use a single fixed or variable ai extent and the size of the fixed extent is not big enough or the variable extent cannot grow because of lack of diskspace or Progress limitations, Progress will terminate.
When you use multiple fixed or variable ai extents, Progress will switch to the next extent if its empty. Otherwise Progress will terminate unless you have started the server/broker with the -aistall option, then Progress will wait before switching to the next extent until it is marked as empty.
If possible always have extra disk space available if for some unforeseen reason the After Image file is growing beyond the size you have estimated.
ONLINE PROCEDURES OR UTILITIES:
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Promon R&D
FIX:
An Alternate approach is as follows:
The best way to do this is by taking a sample of how much BI activity goes on.
For example: If you want to see how much AI space will be used in a 24 hour period, If the system load remains constant for that 24 hours, then use promon and see how many checkpoints happen for a period of time (let's say 15 minutes), then take the number of checkpoints * 4 = number of checkpoints per hour. Now take that number and multiply 24 which gives the number of checkpoints per day. Now take that number and multiply by the BI cluster size to see how much AI space will be used in a 24 hour period.