Why strict memory overcommit matters for Postgres

Memory overcommit is a Linux policy where the kernel allows more memory commitments than the physical memory available, which can lead to issues for applications like Postgres. When memory demands exceed physical capacity, the kernel's Out-Of-Memory (OOM) killer may terminate processes, potentially causing Postgres to assume corruption and restart, affecting all connections. Postgres prefers a strict overcommit policy (vm.overcommit_memory = 2), which prevents such scenarios by refusing memory allocations once a commit limit is reached, resulting in a more controlled failure. This strict policy allows Postgres to handle out-of-memory errors gracefully, affecting only the specific query rather than the entire instance. ClickHouse Managed Postgres implements this strict policy, setting commit limits based on available memory to ensure system stability even under high memory usage. This approach allows for better handling of memory exhaustion, as demonstrated in tests where strict overcommit resulted in fewer disruptions compared to the default policy.

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