title: Lambda SQS Trigger Batch window and Batch size not working as expected
body: <p>I have an AWS SQS (Standard Queue) which listens to third party SNS. I have a lambda setup which has SQS trigger with Batch size 10000 and Batch window 300. My SQS receives approx. 150 messages at a time but lambda gets triggered in batches of 20-30 messages at a time even i configured Batch size 10000. I don't understand why this is happening... even the SQS have enough messages and enough time (300 seconds Batch window) to fill the batch, its not doing it.</p>
  <p>I googled for the issue and found that maximum payload size for lambda can be 6MB. I checked my message and its approx. 2.5 KB per message. so 30*2.5 = 75 KB only and not touching the limit 6MB.</p>
  <p>Additionally, I suspected lambda concurrency so i have set it up to value 1 only. so no parallel lambda instances.</p>
  <p>Can somebody help me to understand where the problem is please?</p>