How PGSizer Computes PostgreSQL 17 Buffer Pools, PgBouncer Slots & NVMe Headroom
In our deterministic PGSizer sizing engine, we derive every hardware tier and postgresql.conf setting from official PostgreSQL 17 documentation, Linux page-cache mechanics, and public vendor pricing retrieved 2026-11-12 — never from unverified benchmark claims.
1. Hot Index Working-Set Residency & shared_buffers Math on PGSizer
Our formula sizes server RAM so active 8KB B-Tree internal/leaf pages and pgvector HNSW neighbor layers remain resident across shared_buffers and Linux page cache:
RAM_Required_GB = (Dataset_GB * Working_Set_Ratio) + Backend_Fork_RAM + OS_WAL_Guard
OLTP SaaS = 0.22 | Fintech Ledger = 0.28 | Analytical HTAP = 0.32 | PostGIS/pgvector = 0.42
shared_buffers = 25% of RAM (30% Hybrid) | effective_cache_size = 75% of RAM2. OOM-Safe work_mem Bounds via PgBouncer Multiplexing on PGSizer
Because PostgreSQL allocates work_mem per sort/hash node per active backend rather than per query, multiplexing client sockets via PgBouncer allows higher spill-free work_mem safely:
Safe_Sort_Pool_MB = Total_RAM_MB * 0.22
work_mem = clamp((Safe_Sort_Pool_MB / Active_Sort_Operations) * Workload_Factor, 4MB, 256MB)3. MVCC Bloat, WAL Compression & 25% NVMe Free-Space Guard on PGSizer
Filling PCIe NVMe drives past 80% degrades controller garbage collection and blocks online pg_repack rebuilds, so we enforce a strict 1.25x free-space multiplier:
NVMe_Disk_GB = ceil(((Dataset_GB * Disk_Overhead_Factor) + WAL_Archive_GB) * 1.25)
random_page_cost = 1.1 | io_combine_limit = '128kB' (PostgreSQL 17 Vectorized I/O)