PACELC Theorem
ELI5 — The Vibe Check
PACELC is CAP theorem's smarter older sibling. It says: during a Partition, choose between Availability and Consistency. But ELSE (when things are normal), choose between Latency and Consistency. Because even when your network is fine, there's still a trade-off between speed and correctness. Real life is complicated.
Real Talk
The PACELC theorem extends CAP by addressing the latency-consistency trade-off during normal operation. It states: if there is a Partition (P), choose between Availability (A) and Consistency (C); Else (E), choose between Latency (L) and Consistency (C). For example, Cassandra is PA/EL (available during partitions, low latency normally) while CockroachDB is PC/EC (consistent in both cases).
When You'll Hear This
"PACELC explains why Cassandra is fast but eventually consistent even without failures." / "CAP only tells half the story, PACELC covers the normal case too."
Related Terms
CAP Theorem
The CAP theorem says a distributed database can only guarantee two out of three things: Consistency (everyone sees the same data), Availability (every requ...
Distributed Database
A distributed database spreads your data across multiple computers that work together like a hive mind. If one server dies, the others pick up the slack.
Eventual Consistency
Eventual consistency means 'give it a moment and everything will match up.' You write data to one server, and the other servers will get the update...
Strong Consistency
Strong consistency means the moment you write something, everyone everywhere immediately sees the updated value. No 'give it a sec' nonsense.