Uncommitted reads see concurrent changes

Code reviewDatabases & SQLSenior–Staff~28 min

Review this Java (JDBC) reconciliation routine that asserts debits equal credits.

What a strong answer looks like

Separate real bugs from style. Rank issues by severity, point at the root cause rather than the symptom, and suggest a concrete fix, specific and kind.

0:00 of about 28 min

Mark a line and say what kind of problem it is.0 findings

1void reconcile(Connection conn, long batchId) throws SQLException {

2 conn.setAutoCommit(false);

3 long debits = scalar(conn,

4 "SELECT COALESCE(SUM(amount),0) FROM ledger "

5 + "WHERE batch_id = ? AND kind = 'D'", batchId);

6 long credits = scalar(conn,

7 "SELECT COALESCE(SUM(amount),0) FROM ledger "

8 + "WHERE batch_id = ? AND kind = 'C'", batchId);

9 if (debits != credits) {

10 alert("Imbalance in batch " + batchId);

11 }

12 conn.commit();

13}

Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.