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Vic Sun · Sep 9, 2021

Hello Muhammad,

Either documentation page explains the difference:

Embedded Language Development > ObjectScript > ObjectScript Reference > ObjectScript Functions > $INCREMENT

https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls?KEY=RCOS_fincrement#RCOS_fincrement_seq

"$SEQUENCE and $INCREMENT can be used as alternatives, or can be used in combination with each other. $SEQUENCE is intended specifically for integer increment operations involving multiple simultaneous processes. $INCREMENT is a more general increment/decrement function.

$SEQUENCE increments global variables. $INCREMENT increments local variables, global variables, or process-private globals.

$SEQUENCE increments an integer by 1. $INCREMENT increments or decrements any numeric value by any specified numeric value.

$SEQUENCE can allocate a range of increments to a process. $INCREMENT allocates only a single increment.

SET $SEQUENCE can be used to change or undefine (kill) a global. $INCREMENT cannot be used on the left side of the SET command."

Hope that helps!

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Steven Hobbs · Sep 15, 2021

Aside from several arithmetic differences, the biggest difference between $INCREMENT AND $SEQUENCE occurs when "SET index=$INCREMENT(^global)" versus "SET index=$SEQUENCE(^global)" are being executed by multiple processes.

All the processes evaluating $INCREMENT(^global) on the same ^global variable will see a sequence of increasing integers.  No two processes will see the same integer returned.  The integers are given out in strict increasing time order and no integer value is skipped.

All the processes evaluating $SEQUENCE(^global) on the same ^global variable will see a sequence of increasing integers.  No two processes will see the same integer returned.  Because blocks of integers are assigned to processes, it is possible for one process to receive a larger integer in the sequence before some other process receives a smaller integer in the sequence.  If some process decides to stop processing integer values at some point then the larger integer values assigned to that process will be skipped and not returned as part of the sequence.

The $SEQUENCE function can have less multi-process overhead because integers in the sequence are assigned in blocks but $SEQUENCE does not guarantee a sequence of numbered tasks is assigned to processes in strictly increasing order.  Every process must continue processing numbered tasks until that particular process has been assigned a sequence number larger than the highest assigned task.  Just because one process has finished the highest assigned task does not mean that other processes are done with the earlier tasks (or have even started earlier tasks) and the sequence is only complete when every process has received a sequence number larger that the number of the final task.

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