First error: Exceeded max size limit of 6000000 OR Exceeded max size limit of 12000000 - Solution

Hello Trailblazers, in this post we're going to talk about the resolution of a very common error as given below:

First error: Exceeded max size limit of 12000000 OR First error: Exceeded max size limit of 6000000 

This error appears when you've exceeded the heap size limit in a single transaction. The heap size limit for a synchronous transaction is 6MB and for an asynchronous transaction is 12MB. Asynchronous transactions basically consists of batch classes, future methods and queueable apex.

How to resolve this error?

You need to reduce the heap size in order to resolve this error. Heap size is basically the memory that your code is taking up while executing. It is the sum of all the memory your variables, maps, sets, lists or any other data structure is consuming. In order to resolve the error you need to reduce the heap size. Below are some tips to help you out:

1. Use Limits.getHeapSize() to understand how much heap size (approx) is used in the current transaction upto a particular point.

2. Use Limits.getLimitHeapSize() to get the total amout of heap size available in the current transaction.

3. Use SOQL For Loops, if you use SOQL for loops the result of the query is given in the batch of 200 records while using a list variable or a single record is returned while using a single instance variable. In both the cases, lesser memory is consumed as we're only storing a maximum 200 records at a time (compared to 50,000 records queried in a single SOQL statement).

List<Account> accounts = [SELECT Id FROM Account];
// Stores 50,000 records at max - greater heap size

for(List<Account> accounts : [SELECT Id FROM Account]) {
}
// Stores 200 records at max - lesser heap size

4. Manage your code effectively using helper functions - Avoid class level variables.

void callMe()
{
    List<Account> accounts = [SELECT Id FROM Account];
    System.debug(Limits.getHeapSize()); // Coming as: 321085
}
callme();
System.debug(Limits.getHeapSize()); // Coming as: 1044

As you can see above, the heap size is reduced after the function call is complete because the call stack is now empty and the local variables are destroyed.

5. Clear the lists/map/set/variables which are not in use or make them null

These are some of the tips that can be used to prevent the heap size limit error. Make sure to write effective code when working with large data. If you have any other suggestion, do comment it down below and I'll include that in the blog post. 

That's all for this tutorial everyone I hope you liked it, the full code used in this post can be found here. Do let me know your feedback/thoughts in the comments down below.

Sharing a Salesforce Help Article related to this error: https://help.salesforce.com/s/articleView?id=000321537&type=1

Happy Trailblazing!!