Blog · page 9
Notes on engineering, design, and everything in between.
Memory layout: the same algorithm, ten times slower, is usually cache
A trip to main memory costs hundreds of cycles; a cache line fetch costs one. Sequential versus random access often outweighs the algorithmic order itself.
Deadlock: break any one of four conditions
Mutual exclusion, hold and wait, no preemption, circular wait. All four must hold at once. The practical one to break is circular wait: give every lock a global order.
The N+1 query: the most typical ORM performance trap
Fetch 100 rows and query the relation for each one and you have made 101 queries. There are only three fixes: eager load, batch fetch, or use a single join.
Rate limiting: what token bucket and leaky bucket really differ on
A token bucket permits bursts; a leaky bucket flattens traffic to a constant rate. Picking wrong shows up as throttled normal users, or a limit that does nothing.
Catastrophic backtracking: why a regex can pin a CPU
Nested quantifiers make the number of match attempts grow exponentially; (a+)+b can hang a process on one long non-matching input. Drop the nesting or put a timeout on it.
iframe sandbox: it narrows capability, it does not harden
The sandbox attribute starts by removing everything and allow-* adds pieces back. Getting the direction backwards is common: scripts stop running because that is the default.