The app got slower as pages grew, and the reason was not the queries. It
was their number.
A transaction is pinned to one connection, and a connection runs queries
one after another. Every Promise.all in a withUser block looked like
concurrency and was a queue. Measured against the real database: the
round trip is ~36 ms, ten trivial `select 1` over one connection take
343 ms, over ten connections 39 ms. Nothing here is slow — the whole
dashboard payload is under 200 kB, and every table is around a thousand
rows.
More connections is the wrong answer: the RLS session context is per
transaction, so parallel reads mean parallel transactions, and those
multiply the connections the database will grant. Fewer round trips
instead. Postgres will return each sub-select as its own JSON column of
one result.
Per page view, counting the transaction frame:
shell (paid by every page) 10 → 4
overview 14 → 5
employee file 14 → 7
employee list 8 → 6
The overview plus its shell went from 24 round trips to 9 — about 860 ms
of pure waiting down to about 320 ms.
The one trap is documented where it bites: inside json_agg, Postgres
formats values itself and the driver's parsers (lib/db/pool.ts) never
see them. Dates, numerics and uuids come out identical; timestamptz does
not — "+00:00" where the driver gives "…Z". Timestamps are compared as
strings in lib/history.ts to decide what happened later, and those two
forms sort against each other wrongly. Every timestamptz in a bundled
query therefore goes through zeitstempel(), which was checked
character-for-character against the driver.
Four loaders moved out of their pages into lib/ so the number of round
trips can be measured without building a React tree, and so the new path
could be held against the old one field by field: same rows, same order,
same strings, for the overview and for four employee files chosen to
differ (with history, a chief, a planned entry, one with dependents).
withUser now counts the queries in each transaction and says so in
development past a threshold. Without that, this grows back: each new
tile brings its own query, and nobody notices until everybody does.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Maximilian Stubhan
91b2b3406b