Transaction Isolation, Durability, and Limits

Two reads of Alice's balance, made one after the other, can return two different numbers. The reason is isolation, the third ACID property. Below, we test isolation and durability on the bank transfer, and then look at how transactions are retried and what limits they have.

The examples continue with the bank database and the transaction.js script from the Transactions in MongoDB lesson, where one transfer left Alice with 50 and Bob with 250. Transactions still need the replica set from that lesson. If you have run other tests since then, reset the two balances in mongosh:

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