[CORRUPTED] Synthetic Benchmark PR #20106 - fix: resolve race condition in compound trigger evaluation

[tomerqodo]

Benchmark PR PrefectHQ#20106

Type: Corrupted (contains bugs)

Original PR Title: fix: resolve race condition in compound trigger evaluation
Original PR Description: ## Summary

Fixes two race conditions in compound trigger evaluation:

1. Never-firing race (transactional): Advisory locks serialize concurrent evaluations
2. Double-firing race (autocommit): DELETE ... RETURNING makes clearing a claim operation

Race Condition 1: Never-firing (with transactions)

When two child triggers fire concurrently in separate transactions, each only sees its own uncommitted insert due to READ COMMITTED isolation:

Transaction T1 (event A):              Transaction T2 (event B):
  │                                      │
  ▼                                      ▼
  INSERT child_firing A                  INSERT child_firing B
  (uncommitted)                          (uncommitted)
  │                                      │
  ▼                                      ▼
  SELECT child_firings                   SELECT child_firings
  → sees only A (own insert)             → sees only B (own insert)
  │                                      │
  ▼                                      ▼
  ready_to_fire? NO (1 of 2)             ready_to_fire? NO (1 of 2)
  │                                      │
  ▼                                      ▼
  COMMIT                                 COMMIT

Result: Both firings are now in database, but parent never fired!

Fix: PostgreSQL advisory locks serialize concurrent evaluations.

Race Condition 2: Double-firing (with autocommit)

When both workers see all firings, both delete and both fire:

Worker A:                              Worker B:
  SELECT child_firings → [A, B]          SELECT child_firings → [A, B]
  ready_to_fire? YES                     ready_to_fire? YES
  DELETE child_firings                   DELETE child_firings
  (succeeds)                             (succeeds - rows already gone)
  FIRE parent                            FIRE parent

Result: Parent fires TWICE!

Fix: DELETE ... RETURNING makes clearing a claim. Only the worker that successfully deletes proceeds.

Changes

• src/prefect/server/events/models/composite_trigger_child_firing.py:
  • Added acquire_composite_trigger_lock() for advisory locking
  • Updated clear_child_firings() to use DELETE ... RETURNING
• src/prefect/server/events/triggers.py:
  • Acquire advisory lock before evaluation
  • Check return value of clear_child_firings() before firing
• tests/events/server/triggers/test_composite_triggers.py:
  • Added regression tests for concurrent child firing scenarios

🤖 Generated with Claude Code
Original PR URL: PrefectHQ#20106