Template:SirTune size requirement for SIRTUNED

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It is recommended that you do not spend a lot of time trying to size SIRTUNED, because the consequences of under- or over-estimating the SIRTUNED space requirements are relatively benign. However, if you do want to size SIRTUNED, this page provides some basic rules of thumb for estimating the correct size.

A formula for the estimate

The size of SIRTUNED is mainly determined by these factors:

  • The number of lines of compilations saved. This is the number of lines in precompiled APSY procedures compiled in the run, or if the ALLCOMP statement is specified for SirTune, the number of lines of all compiled procedures. In any case, a line counts as 1 each time it is compiled.
  • The number of samples collected.
  • The average number of users for which data is collected per sample.

To estimate the number of lines of compilations saved when the ALLCOMP statement has not been specified, and when subsystems are not START'ed and STOP'ed multiple times in a run, simply total the number of lines in all precompiled procedures in START'ed subsystems. To get an estimate of this:

  1. Count the total number of precompiled procedures.
  2. Estimate the average number of lines per precompiled procedure by entering the editor for a representative sample of them.
  3. Multiply these two values.

Call the number of compiled lines COMP_LINES.

To estimate the number of samples, divide the number of seconds over which data is to be collected, by the sample interval length (1 or whatever was specified on the INTERVAL statement). Call this value NUM_SAMP.

The best guide to estimating the number of users for which data is collected per sample is the Model 204 performance monitor. There are certain worst-case values that one can assume, however:

  • If only state RUNG is being collected, at most 1 user will have data collected per sample, unless MP/204 is installed (in which case, the upper limit is 1 plus the number of subtasks).
  • If only REDY, RUNG, BLKIN, BLKIU, SWPGI, SWPGOW, SWPGOBN, and/or SWPGOBU states are being collected, the upper limit is the number of servers.
  • Otherwise, a crude upper limit is the number of users.

Call whatever value one comes up with AVG_USERS.

The total number of bytes required for SIRTUNED can be estimated by this:

100,000 + ( 12 * COMP_LINES ) + ( NUM_SAMP * 64 * ( 1 + AVG_USERS ) )

This estimator provides a fairly generous estimate without being excessive. To determine the number of disk tracks required, divide the number of bytes produced by this estimator by the number of bytes per track at the block size for SIRTUNED (46,952 is the default bytes per track on a 3380, and 55,996 is the default on a 3390).

An example estimate

Suppose a shop has 100,000 lines of pre-compiled User Language code, expects to collect samples over 8 hours at 1 per second, is collecting data for states RUNG, REDY, and BLKIN, and has 30 servers defined in the Online. These factors are clear:

COMP_LINES = 100,000 NUM_SAMP = 8 * 60 * 60 / 1 = 28,800

Since all the users in a collected state must be in a server, use the number of servers as a gross estimator for AVG_USERS, that is:

AVG_USERS = 30

This means that the estimated space requirements in this case is:

100,000 + ( 12 * 100,000 ) + 28,800 * 64 * ( 1 + 30 ) = 58,439,200

If the sample data was going to a 3380 with the SirTune default block size, it would require 1245 tracks or 83 cylinders.

The number of samples collected in this example is fairly extreme: generally there is not much benefit to collecting more than 10,000 samples. If sampling is limited to some key hours to restrict the number of samples collected to 10,000, the estimator becomes:

100,000 + ( 12 * 100,000 ) + 10,000 * 64 * ( 1 + 30 ) = 21,140,000

If the sample data in this case was going to a 3380 with the SirTune default block size, it would require 451 tracks or 31 cylinders.

See also

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