[SalesForce] Performance comparison – repeat loop vs more in one loop

I'm trying to optimize some code and am going through some triggers. I'm wondering if there is a performance difference between

running three methods in series – and in each one, I loop over
Trigger.new twice to pull an Id and then update the record from the
parent record – and
combining the methods and looping only twice, but doing more script
statements in each loop iteration

The total script statements executed will be identical. This question is specifically if the number of loops executing those script statements should have an effect on application speed.

Best Answer

In general less loops is better, as this can lead to better chances to not thrash the L2 cache on the CPU, however there are so many levels between there and your apex code that the odds of you actually seeing any measurable difference is nil.

For triggers, performance is totally dominated by db access by a large margin, so that's the best place to concentrate on perf (make as few db calls as possible, access as little db data as possible, things that the governor limits already incentives you to do).

For apex code that's not touching the db,and doing approx the same number of script statements, don't sweat it, pick the version that's the most understandable/maintainable.

Related Solutions

[SalesForce] For loop within for loop

You should never do DML statements (such as insert) inside loops, this will easily get you off limits. Create a List outside the loop, iterate over your trigger in the first loop, create new records and add them to the list in the second loop, then insert everything outside the loop. Something like this:

List<Revenue_Schedule__c> new_records = new List<Revenue_Schedule__c>();

for (Your_Trigger_sObject__c current : trigger.new) {
    Integer numOfMonths = current.start_date.monthsbetween(current.end_date);
    for (Integer i=0; i < numOfMonths; i++) {
        new_records.add(
            new Revenue_Schedules__c(
                Amount__c = current.amount / numOfMonths,
                Date__c = current.start_date.addmonths(numOfMonths), 
            )
        );
    }
}

insert new_records;

The important is to keep the DML operation outside the loop. The same applies to queries, keep them always out.

[SalesForce] See Number of Queries Executed in Call-chain

Use Profiling. By going in to the Developer Console, you can go to Debug > Change Log Levels, then modify the debug logging to include "Profiling" set to "FINEST". From there, run your execution, and afterwards, you'll get a section in your debug logs that show you which queries were executed, and how many times.

For example, here's an example from my dev org:

09:38:20.332 (1332704580)|CUMULATIVE_PROFILING|SOQL operations|
Trigger.myNS.myTrigger: line 12, column 1: [
            SELECT AccountId Id, COUNT(Id) total FROM Opportunity
            WHERE AccountId = :accountSum.keySet() GROUP BY AccountId]: executed 5 times in 13 ms

This shows that a query was executed 5 times, from a particular trigger (it could also be a class, such as Class.myNS.myClass). From there, you can determine both how many times it executed and how long it took in "database time", which affects the length of the transaction. This will give you an idea on where to focus your optimization efforts.

Best Answer

Related Solutions

[SalesForce] For loop within for loop

[SalesForce] See Number of Queries Executed in Call-chain

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