fsync, write caches and the SSD that lies about durability
A committed transaction is only safe once the bytes reach durable storage. Somewhere between the database and the flash chips, there are caches that may not survive a power cut.
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Cache stampedes: what happens when a hot key expires
A popular key expires, and a thousand requests all miss at once and recompute the same expensive value against the database. The cache made things worse.
Schema changes without downtime: the lock queue problem
A fast ALTER TABLE can still take your site down, if it waits behind one slow query while every new query waits behind it.
PHP enums and readonly: what they fix and where they bite
Backed enums replace string constants and magic values. Readonly properties give you immutable value objects. Both have rules that surprise people in frameworks.
Cross rates: how EUR/GBP is built from two dollar pairs
Most currencies are quoted against the dollar. A cross such as EUR/GBP is either traded directly or derived from two USD pairs, and the derivation is simple division.
Forward points: where the forward price comes from
A forward exchange rate is not a forecast. It is spot adjusted for the interest rates of the two currencies, so the higher-rate currency trades at a forward discount.
Spot forex has no real volume: what platforms show instead
The volume bars on a forex chart are tick counts from one broker's feed. Real volume exists for currency futures, and using it takes a few conversions.
Why a Bitcoin fee depends on bytes, not on the amount
Miners are paid per unit of block space. Fee rates are quoted in sat/vB, and the address type you use changes how many vbytes the same payment takes.
Perpetual futures: how funding works and who pays whom
A perpetual contract has no expiry, so a periodic payment between longs and shorts keeps its price close to spot. The exchange does not receive it.
