caching – Page 6 – Türker Yıldırım

Transients without an object cache live in options forever

NoteJuly 22, 20212 min read

A transient with an expiry is stored as two rows in the options table, and nothing deletes an expired one until something asks for it. Expired transients are…

maxmemory-policy, and the cache that was a database

NoteJune 7, 20212 min read

The default policy is noeviction, which means a full Redis returns errors on writes rather than evicting anything. noeviction is the right default for an instance holding queue…

An index that made writes slower than the reads it saved

Deep diveApril 23, 202110 min read

Eleven indexes on a table with a heavy write path. Every index is a write amplification that nobody measured, and three of them were never used.

A read model that is allowed to be wrong for four seconds

Deep diveMarch 17, 202114 min read

A report query with eleven joins, run on every dashboard load. One model cannot be shaped for both writing and reading past a certain size.

The cache that returned stale data for eleven days

Deep diveMarch 4, 202110 min read

A price change that took eleven days to reach one page. Three caches, and only one of them was being cleared.

Redis 6.2 GETDEL, for the one-shot token

NoteFebruary 23, 20211 min read

Reading a key and deleting it was two commands and a race, and 6.2 made it one. The race matters for anything single-use — a password reset token,…

SINTERCARD counts without materialising

NoteFebruary 15, 20212 min read

Counting the intersection of two large sets meant building the intersection first, which allocates a set you immediately discard. The LIMIT is the part that changes what is…

COPY, and the key you no longer DUMP and RESTORE

NoteFebruary 11, 20212 min read

Duplicating a key used to mean serialising it out and back in, which moved the whole value through the client for no reason. Staying server-side matters for a…

ZRANGESTORE, and the sorted set you were rebuilding

NoteFebruary 11, 20212 min read

Taking a slice of a sorted set into a new key required reading it into the client and writing it back, which is O(n) over the network. The…

Profiling before you optimise

Deep diveNovember 5, 202010 min read

Two days spent optimising a function that was 3% of the request. The profiler said so in ninety seconds, and nobody had run it.