If my database is ACID, why do I still see race condition bugs?

ACID guarantees apply to what happens inside a transaction, at the isolation level you are actually running. Most databases default to Read Committed, which still allows anomalies like lost updates when you read, compute in the app, and write back. Fixes include doing the read-modify-write in one SQL statement, using SELECT FOR UPDATE, or raising the isolation level.

What does BASE mean and when is it acceptable?

BASE stands for Basically Available, Soft state, Eventually consistent, and it describes stores that relax ACID to gain availability and scale. It fits data where temporary staleness is harmless: feeds, counters, caches, analytics. It is a poor fit for money, inventory, or anything where two nodes briefly disagreeing creates real-world cost.

Does a COMMIT guarantee my data can never be lost?

It guarantees the data survived to stable storage on that machine, assuming full durability settings. It does not protect against the disk itself dying or the data center burning down. For those you need replication, ideally synchronous so the commit waits for a second machine, plus backups for the truly bad days.

Fundamentalschapter 5 of 6 · 4 lessons

ACID Properties

The guarantees that make relational databases trustworthy for transactions.

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You move 200 pounds from savings into your current account. The database subtracts 200 from one row. Then the machine loses power.

The money is gone. Not delayed, gone: taken off one account, never added to the other, and nothing in either row records that a transfer was halfway through.

ACID is four promises a database makes so that afternoon never happens. Each one exists because that exact disaster happened to somebody first, and half the history of the databases that dropped them is the story of those disasters coming back.

Lessons

4 in this chapter

AtomicityEvery statement in the transaction commits, or none of them do.3 min
ConsistencyTransactions move the database from one valid state to another, never through an invalid one.2 min
IsolationConcurrent transactions should behave as if they ran one at a time.3 min
DurabilityOnce the database says committed, a crash cannot take it back.2 min