What means ensure control of transaction isolation levels in databases?

The control of transaction isolation levels in databases is ensured by the following means:

• Isolation Levels — the SQL standard defines several levels: Read Uncommitted, Read Committed, Repeatable Read, Serializable. Each level restricts the visibility of changes made by other transactions.

• Locking mechanisms — databases use locks at the row, page, or table level to prevent concurrent access that could lead to anomalies.

• Multiversion Concurrency Control (MVCC) — some DBMSs (e.g., PostgreSQL) use MVCC, allowing transactions to see a consistent state of data without locks.

• Transaction settings in code — in Go, for example, when working with a database through drivers, you can set the isolation level via transaction methods.

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

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

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