Tell us about transaction isolation levels.

Transaction isolation levels determine how much one transaction can see the changes made by others and how they affect each other. The SQL standard defines four main levels of isolation:

1. Read Uncommitted

   • A transaction can see changes made by other transactions even if they are not yet committed (dirty reads).
   • Problems can include dirty reads, non-repeatable reads, and phantom reads.

2. Read Committed

   • A transaction only sees data that has been committed by other transactions.
   • Dirty reads are prevented, but non-repeatable reads and phantom reads can occur.

3. Repeatable Read

   • Ensures that repeated reads of the same data within a transaction are consistent.
   • Prevents dirty reads and non-repeatable reads, but phantom reads can still occur.

4. Serializable

   • The strictest level of isolation.
   • Transactions are executed as if they were sequential, one after another.
   • All read anomalies, including phantom reads, are prevented.

In Go, when working with databases via database/sql, you can set the isolation level through driver methods or SQL queries, for example:

tx, err := db.BeginTx(ctx, &sql.TxOptions{
    Isolation: sql.LevelSerializable,
})

Choosing an isolation level affects performance and concurrency: stricter levels reduce conflicts but may decrease throughput due to locking.