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My application is running inside AWS lambda and needs to write to postgresql. There is a scenario that two lambdas will write to the same row in the db table. Below is the case:

Lambda1: receive order processing event then update order#1 status to processing

Lambda2: receive order completed event then update order#1 status to completed.

In above scenario, Lambda1 and Lambda2 can happen in any order. how can I make sure the final status of the order#1 is completed not processing?

I can do a query before update, but what happen if the other lambda writes to the table in between?

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  • Postgres does row level locking for writes like that. As long as lambda1 starts its write first, it will be fine. Commented Feb 16, 2021 at 22:42
  • Locking a specific row in postgres Commented Feb 16, 2021 at 23:20
  • The problem in my case is that lambda1 and lambda2 may run in different order Commented Feb 16, 2021 at 23:22
  • How come lambda2 can run before lambda1? I think this is architecture design issue, not postgresql problem? Commented Feb 17, 2021 at 0:27
  • yes, this is architecture design issue. I am using event sourcing design and the events come to my lambda can be in any order. So that I need to fix in my lambda. The question is what is the best way to handle this case? Commented Feb 17, 2021 at 2:13
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