Heap Size #inSalesforce

Heap Size #inSalesforce

Salesforce enforces an Apex Heap Size Limit of 6MB for synchronous transactions and 12MB for asynchronous transactions.

'Apex heap size too large' occurs when too much data is being stored in memory during processing. The limit depends on the type of execution.

Example:

@isTest
private class heapCheckIssue{
    static testMethod void myTest(){
        String tStr = 'aaaaa bbbbb ccccc ddddd eeeeee fffff ggggg 11111 22222 33333 44444';
        List<String> baseList = tStr.split(' ');
        List<String> bigList = baseList;
        Map<integer, List<String>> SampleMap = new Map<integer, List<String>>();
        SampleMap.put(1, bigList);
        
        for (integer i=0; i<50; i++) {
            List<String> tempList = new List<String>();
            tempList = SampleMap.get(1);
            bigList.addAll(tempList);
        }
        system.debug('FINAL LIST SIZE IS '+bigList.size());
    }
}

Here, the List baseList, the value of SampleMap and the List tempList are pointing to the same memory address. As a result, the heap size doubles with each iteration of the loop.

Solved:

@isTest
private class heapCheckSuccess{
  static testMethod void myTest(){
    String tStr = 'aaaaa bbbbb ccccc ddddd eeeeee fffff ggggg 11111 22222 33333 44444';
    List<String> baseList = tStr.split(' ');
    Map<integer, List<String>> Sample = new Map<integer, List<String>>();
    List<String> bigList = baseList;
    Sample.put(1, bigList);
    List<string> myList = new list<string>(); //Declare a new list
    for (integer i=0; i<50; i++) {
      List<String> tempList = new List<String>();
      tempList = Sample.get(1);
      system.debug('templist: ' + tempList.size());
      system.debug(' bigList: ' + bigList.size());
      myList.addall(tempList); //original code is  bigList.addall(tempList);
    }
    system.debug('FINAL LIST SIZE OF bigList IS '+ bigList.size());
    system.debug('myList IS '+mylist.size());
  }
}

The heap size does not get too large because we are using a new List to store the value of tempList in each iteration and then appending the list, instead of using bigList variable.

Reference:

https://help.salesforce.com/s/articleView?id=000384468&type=1