Detect account balance changes in a transaction

Question

I'm trying to analyze transactions, but I can't get answers to some questions.

1. In this transaction: 37YEqu9NVmAd6wiV9HaQkoQgrPJzooxC1Hhwors43daJbAQHbHzcoqxJF8PL94YKt8CUaBMu71UW8pjjVRrXiEFS length of meta.postBalances is 42, and the length of transaction.message.accountKeys is 13. How do I know which account balances meta.postBalances[13:41] represents if there are no corresponding accounts in transaction.message.accountKeys?

2. What does it mean when the length of meta.preTokenBalances is not equal to the length of meta.postTokenBalances? e.g 33Xh1SnWZ6gJVUsPG6xXfis9FjamEgaYWYzBo3xSenyb5kpJbDGkfpG6LMBtUpLMaaEn37FSptKZsEpiK28PiCTo

Answer 1

1. This transaction uses address-lookup-tables, which are special accounts that store addresses. Transactions may reference addresses stored inside of the address-lookup-table during construction, reducing the size of the transaction. You can find more information about these at https://docs.solana.com/developing/lookup-tables. To answer your question, you'll also need to look in the loadedAddresses array when loading the transaction.

2. It looks like account 5y9RGK1bmQXZ3hv6v8ygU7GcFGam2NDmdtb8KUrgPo5y was created during this transaction, so it had no balance to start, and ended with some balance. I'm not 100% sure on this, but it's the only difference that I can see.