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…ransaction S034 catches the single-function shape: a loop inside an atomic block whose body opens a nested atomic block or calls get_or_create or update_or_create. Past 64 such savepoints in one transaction Postgres overflows its subtransaction cache and slows every query. Existing loops are pinned in a shrink-only allowlist.
Class bodies run where they are defined, so they keep the enclosing transaction; async queryset methods open savepoints too.
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resolves INFRENG-846
Adds flake8 rule S034: it flags a loop that runs inside a transaction and opens a savepoint on every iteration (a nested
atomicblock, orget_or_create/update_or_createand their async versions). Once one transaction holds more than 64 savepoints that wrote something, Postgres overflows its subtransaction cache and every query on that database slows down while the transaction stays open.What it catches: the transaction and the loop in the same function, the savepoint opened directly in the loop body. That includes
@transaction.atomicfunctions,outbox_context(transaction.atomic(...))blocks, and comprehensions.What it does not catch, on purpose, to stay a cheap per-file check: a transaction opened by a caller, a savepoint opened by a function the loop calls (including a model's own
save()), and anything decided at run time. It also cannot tell a loop over a short fixed list from one over customer data, so short fixed loops need a# noqa: S034with a reason. Sizes and leaked transactions are left to production monitoring and to the task connection cleanup in #130665.The 11 existing loops in
src/sentryare pinned in a shrink-onlyS034_allowlist, like S030. getsentry loads this plugin, so getsentry/getsentry#23210 exempts its three hits and has to merge first.