Problem Faced:

• Users attempt to spend the same UTXO (Unspent Transaction Output) multiple times.
• Lack of blockchain confirmations allows fraudulent deposits.
• Database inconsistency issues lead to incorrect balances.

Solution:

• Unconfirmed Transaction Check: Ensure blockchain confirmations before crediting deposits.
• Atomic Transactions: Use BEGIN TRANSACTION and COMMIT to update balances.
• Rate Limiting: Detect multiple spend attempts and flag them.

PostgreSQL Transaction Check to Prevent Double-Spending:
sql

BEGIN TRANSACTION;

SELECT * FROM transactions WHERE txid = 'some_txid' AND spent = false;

UPDATE transactions SET spent = true WHERE txid = 'some_txid';

UPDATE users SET balance = balance + 10 WHERE user_id = 123;

COMMIT;

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