Have you worked with transactions in PostgreSQL and with what isolation levels?

Yes, I have worked with transactions in PostgreSQL, including managing isolation levels to ensure data integrity and control concurrency.

PostgreSQL supports four standard transaction isolation levels:

• Read Uncommitted — effectively behaves like Read Committed, as PostgreSQL does not allow dirty reads.
• Read Committed — the default level. A transaction sees only data that was committed at the moment of each individual query.
• Repeatable Read — the transaction sees a snapshot of the data at its start, preventing non-repeatable reads and phantom reads.
• Serializable — the strictest level, providing full transaction isolation as if transactions were executed sequentially.

Example of setting the isolation level in Go using the database/sql package:

import (
    "database/sql"
    _ "github.com/lib/pq"
)

func example(db *sql.DB) error {
    tx, err := db.Begin()
    if err != nil {
        return err
    }
    // Setting the isolation level
    _, err = tx.Exec("SET TRANSACTION ISOLATION LEVEL SERIALIZABLE")
    if err != nil {
        tx.Rollback()
        return err
    }

    // Perform operations within the transaction
    // ...

    return tx.Commit()
}

Using the correct isolation level helps balance performance and data consistency in a multi-user environment.