Listen to this Post
ACID is a foundational set of properties that ensure reliable transactions in relational databases.
🔹 A – Atomicity
→ Guarantees that all operations in a transaction are completed successfully or none are applied at all.
“All or nothing.”
🔹 C – Consistency
→ Ensures that a transaction brings the database from one valid state to another, maintaining integrity rules.
“No rule-breaking allowed.”
🔹 I – Isolation
→ Transactions execute independently. Intermediate states are not visible until the transaction is committed.
“No interference.”
🔹 D – Durability
→ Once a transaction is committed, its results persist even in the event of a system crash.
“Permanent and safe.”
You Should Know:
1. Atomicity in Action (SQL Example)
BEGIN TRANSACTION; UPDATE accounts SET balance = balance - 100 WHERE user_id = 1; UPDATE accounts SET balance = balance + 100 WHERE user_id = 2; -- If any step fails, ROLLBACK undoes all changes COMMIT;
Linux Command (Using `sqlite3` for Testing):
sqlite3 test.db "BEGIN TRANSACTION; UPDATE accounts SET balance = balance - 100 WHERE user_id = 1; UPDATE accounts SET balance = balance + 100 WHERE user_id = 2; COMMIT;"
2. Ensuring Consistency (Constraints in SQL)
ALTER TABLE orders ADD CONSTRAINT fk_customer FOREIGN KEY (customer_id) REFERENCES customers(id);
PostgreSQL Check:
psql -U postgres -c "\d orders" Verifies foreign key constraints
3. Isolation Levels (MySQL Example)
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; START TRANSACTION; SELECT FROM transactions WHERE account_id = 1; -- Other transactions cannot modify until this completes COMMIT;
Check Isolation Level in PostgreSQL:
psql -U postgres -c "SHOW default_transaction_isolation;"
4. Durability via WAL (Write-Ahead Logging)
Enable WAL in PostgreSQL:
echo "wal_level = replica" >> /etc/postgresql/14/main/postgresql.conf systemctl restart postgresql
Verify Durability in SQLite:
sqlite3 test.db "PRAGMA journal_mode=WAL;"
5. ACID Compliance in NoSQL (MongoDB Example)
db.runCommand({
beginTransaction: 1,
txnNumber: NumberLong(1),
operations: [
{ op: "update", ns: "test.accounts", query: { user_id: 1 }, update: { $inc: { balance: -100 } } },
{ op: "update", ns: "test.accounts", query: { user_id: 2 }, update: { $inc: { balance: 100 } } }
],
commitTransaction: 1
});
MongoDB Durability Check:
mongod --dbpath /data/db --journal Enables journaling for crash recovery
What Undercode Say:
ACID principles are critical for transactional integrity. In cybersecurity, databases without ACID compliance risk corruption, race conditions, and data breaches. Always enforce:
– Atomicity → Use `ROLLBACK` in SQL or compensating transactions in NoSQL.
– Consistency → Apply strict schema validation (CHECK constraints).
– Isolation → Test with `READ UNCOMMITTED` vs. SERIALIZABLE.
– Durability → Enable WAL, journaling, or replication (pg_basebackup in PostgreSQL).
Expected Output:
-- Atomicity test
BEGIN;
INSERT INTO logs (event) VALUES ('ACID Check');
ROLLBACK; -- Entry should NOT persist
-- Durability test
BEGIN;
INSERT INTO logs (event) VALUES ('Durability Passed');
COMMIT;
-- Even after a crash, this log must exist
Prediction:
As distributed databases grow, ACID will evolve with hybrid models (e.g., Google Spanner’s “External Consistency”). Expect stricter compliance in blockchain ledgers.
Relevant URL:
PostgreSQL ACID Compliance Docs
References:
Reported By: Aaronsimca What – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
