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Reserve explicit capacity for ETL and administration.","oltp":"Prefer transaction pooling for large client populations and size PostgreSQL backends for peak active database work plus monitoring, maintenance, and failover margin. Do not map one client connection to one server slot by default.","small":"Use a low ceiling with a pooler and preserve reserved slots. Validate startup shared-memory requirements and do not compensate for connection leaks by repeatedly raising the limit."},"mechanism":["max_connections limits concurrent database-server connections and can only be changed at server start. PostgreSQL sizes some resources directly from it, so raising the ceiling increases allocations including shared memory even when not all slots are busy.","reserved_connections and superuser_reserved_connections carve emergency or privileged capacity out of the same overall ceiling. An application therefore cannot normally consume every configured slot.","A standby must use a value at least as high as its primary. Connection pooling can decouple large client populations from a smaller, controlled number of PostgreSQL backends."],"pitfalls":["Changing the value without planning a restart and keeping standbys at least as high as the primary.","Ignoring shared-memory and per-backend overhead created by a higher ceiling.","Forgetting reserved and superuser-reserved slots when calculating application capacity.","Combining a high connection ceiling with generous per-operation memory settings and assuming the product cannot occur."],"references":[{"title":"PostgreSQL 19 Beta 4: max_connections","url":"https://www.postgresql.org/docs/19/runtime-config-connection.html#GUC-MAX-CONNECTIONS"},{"title":"PostgreSQL 19 release notes","url":"https://www.postgresql.org/docs/19/release-19.html"}],"related":["reserved_connections","superuser_reserved_connections","work_mem","max_worker_processes","max_prepared_transactions","max_wal_senders"],"summary":"The startup-time ceiling on concurrent PostgreSQL client connections and a sizing input for several shared resources."},"enumvals":[],"first_version":"7.4","group":"Connections and Authentication","group_slug":"connection","imported_at":"2026-09-27T17:57:31.67395+08:00","intro_commit":{},"key":"max_connections","last_version":"20","max_val":"","min_val":"","name":"max_connections","position":262,"present_in":["7.4","8.0","8.1","8.2","8.3","8.4","9.0","9.1","9.2","9.3","9.4","9.5","9.6","10","11","12","13","14","15","16","17","18","19","20"],"short_desc":"Determines the maximum number of concurrent connections to the database server.","short_desc_zh":"","source_rev":"english-manuals:eb3142d88d2e4678fa7c215a7cdeff2946fe06cba48b2f6cf4d1d5ae0ca265f3","unit":"","vartype":"integer"}},"Definition":{"Collection":"guc","Key":"max_connections","SourceDatabase":"center","Version":"18","SourceTable":"guc","SourceKey":"max_connections","SourceRevision":"english-manuals:eb3142d88d2e4678fa7c215a7cdeff2946fe06cba48b2f6cf4d1d5ae0ca265f3","Facts":{"boot_val":"100","category":"Connections and Authentication / Connection Settings","context":"postmaster","description":"Determines the maximum number of concurrent connections to the database server. 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