Heap Size Too Large

Salesforce enforces an Apex Heap Size Limit of 6MB for synchronous transactions and 12MB for asynchronous transactions. The "Apex heap size too large" error occurs when too much data is being stored in memory during processing.

Some strategies on how to write Apex scripts that run within heap limits.

 

1. Use soql for loop. This avoid heap size as we are not storing the data in any variable but directly processing it in the loop.

2. Store the required amount of data only. While doing a query usually we retrieve all fields which increases the heap size. One should only query those fields which they will work on. Reduce heap size during runtime by removing items from the collection as you iterate over it.

3. Use local variables instead of class level variable to store large amount of data.   storing data in local variable will go out of scope as soon as the method gets over. This helps in cleaning heap size after use.

4. Use of Transient keyword to declare instance variable that can not be saved, and shouldn't be transmitted as part of the view state for the Visualforce page.

e.g: Transient Integer tempVar ; Some apex objects are automatically considered transient, i.e their value does not get saved as part of the page's view state. These objects are SavePoints, PageReference, XMLStream Classes, etc. Static variables also don't get transmitted through the view state.

5. Use Limit methods. Use heap limits methods in your Apex code to monitor/manage the heap during execution.

Limits.getHeapSize() – Returns the approximate amount of memory (in bytes) that has been used for the heap in the current context.

Limits.getLimitHeapSize() – Returns the total amount of memory (in bytes) that can be used for the heap in the current context.

// check the heap size at runtime
if (Limits.getHeapSize > 275000) {
     // implement logic to reduce
}