Memory-Safe Python Script Patterns

Battle-tested patterns for keeping Python scripts alive under systemd MemoryMax constraints. Extracted from repair_direct_parquet.py (24-worker parallel repair) and exness_tick_cache_seeder.py (10-symbol daily seeder) after 5 OOM optimization cycles on a 62 GB GPU workstation.

Core insight: Python's garbage collector frees objects, but the C allocator (glibc ptmalloc2) does NOT return freed pages to the OS. Without explicit malloc_trim(0), RSS only grows — even after del and gc.collect(). mimalloc with MIMALLOC_PURGE_DELAY helps but explicit purge is faster.

Self-Evolving Skill: This skill improves through use. If instructions are wrong, parameters drifted, or a workaround was needed — fix this file immediately, don't defer. Only update for real, reproducible issues.

The 7 Patterns

1. Cached Allocator Purge

The most important pattern. Cache the ctypes library handle on first call so subsequent purges are a single FFI invocation with zero allocation overhead.

import ctypes
import gc
import sys