Avoid child queries in long running batches.

Recently I was working on a production incident and have found issues with child queries in batch apex where the following stats holds right:

Query: On contact 

Total records: ~0.4 million

Child query filters: Two string and one record type check

Issues:

• CPU timeout error
• Batch will not start.

Solution: Removed child query completely and written logic inside execute method. Please follow code snippet given below:

	global void execute(Database.BatchableContext bc, Contact[] conScopeLst) {
	Set<id> conIds = new Set<id>();
	for (Contact c : conScopeLst) conIds.add(c.Id);
	Map<Id, list<Contact_Child__c>> conChildMap = new Map<Id, list<Contact_Child__c>>();
	for(Contact_Child__c cc : [SELECT Id, contact__c FROM Contact_Child__c WHERE filter1__c = 'filter1' AND filter2__c = 'filter2' AND contact__c =:conIds ]){
	list<Contact_Child__c> tempLst = new list<Contact_Child__c>();
	if(conChildMap.containsKey(cc.contact__c))tempLst = conChildMap.get(cc.contact__c);
	tempLst.add(cc);
	conChildMap.put(cc.contact__c, tempLst);
	}
	//rest of the logic:
	//usage of map
	//list<Contact_Child__c> list = conChildMap.get(----pass contact record id------);
	}

view raw BatchApexAvoidChildQuery.java hosted with ❤ by GitHub