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Entry type: FAQ Entry ID: 23757729, Entry date: 08/18/2006

How can you define the amount of memory required for the performance indicator log of the Windows system monitor (performance monitor)?

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The hard disk space required for a performance indicator log file depends on:

  • the type and number of the performance indicators used
  • the acquisition cycle
  • the duration of the logging (logging time)

In order to avoid a memory problem you should try out the size of a performance indicator log file before running the diagnostics.
This entry describes how you should proceed to do that.

No. Procedure
1 End the configuration of the performance indicator log
The configuration of the performance indicator log should be ended. If you change parameters of a performance indicator log, then it is highly likely that the memory requirement of the associated log file will also change. You should then determine the memory required once again.
2 Make multiple test recordings
Make several test recordings of the performance indicator log in one log file.


  • Make sure that existing files are not overwritten. For this reason you can use sequential numbering of the log file (already set by default).

    Fig. 01

  • You can use the time-triggered starting and stopping of the performance indicator protocol to use logging times of defined lengths. This facilitates subsequent evaluation, because the logging time (difference between start time and end time) doesn't have to be determined separately in addition.

    Fig. 02

  • After a recording you note the sequence number of the recording and the associated logging time. This is not absolutely necessary, but makes the work easier. You can also determine the start and end times for determining the logging time afterwards from the log file.
3 Determine the memory requirement per data record
Determine the size of each log file recorded. For this you open the Windows Explorer and go to the directory in which the log files are located. Switch the view of the Windows Explorer to "Details" if necessary. The log files and their sizes are now displayed in the Windows Explorer. Convert the size of each log file to a standard logging time (e.g. 1 minute) or the size per data record.

The following figure shows the log files in the Windows Explorer.

Fig. 03


The following table shows the memory requirement for the various test recordings.

File name Acquisition interval Acquisition time File size, absolute
File size, standardized
Data record size
performance001_10.blg 15 s 15 min 1,280 85.3 21.3
performance001_11.blg 15 s 5 min 768 153.6 38.4
performance001_12.blg 15 s 15 min 1,856 123.7 30.9
performance001_13.blg 15 s 10 min 1,280 128 32.0
performance001_14.blg 15 s 10 min 1,280 128 32.0
performance001_15.blg 15 s 20 min 2,432 121.6 30.4
performance001_16.blg 15 s 11 hours 84,672 128 32.1
performance001_17.blg 30 s 10 min 960 96.0 48
performance001_18.blg 30 s 10 min 960 96.0 48
performance001_19.blg 30 s 20 min 1,664 83.2 41.6
performance001_20.blg 30 s 40 min 3,136 78.4 39.2
performance001_21.blg 5 s 10 min 4,608 460.8 38.4
performance001_22.blg 5 s 15 min 6,784 452.3 37.7
performance001_23.blg 5 s 5 min 2,432 486.4 40.5
performance001_24.blg 1 s 5 min 11,200 2,240 37.3
performance001_25.blg 1 s 10 min 22,144 2,214 36.9
performance001_26.blg 1 s 10 min 22,144 2,214 36.9

From the table you can see that one data record does not require more than 50 KB in the log file. It can generally be assumed that each data record probably requires less than 50 KB.

4 Calculate the maximum logging time
Using the value determined in Step 3 for the size of a data record, the acquisition interval and size of the free space on the hard disk, you can now calculate the relevant maximum logging time. At the latest once the logging time has expired, you should check the free space, save the log files and if necessary delete some.


Memory requirement per data record = 50 KB
Free memory = 20 GB
Acquisition interval = 15 s
number of data records
= Free memory / memory requirement per data record
= 20 * 1024 *1024 KB / 50 KB
= 419430 data records
logging time
= Maximum
number of data records * acquisition interval
  = 419430  * 15 seconds
  = 1747 hours
  = 72 days

The calculated maximum logging time is approx. 72 days.

It is advisable to free up the memory occupied by the log files in shorter intervals than calculated. Don't wait until there is no more space available on the hard disk.

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