PostgreSQL 17 → 18 GUC diff

Core configuration parameters added, removed, or changed in boot default between PostgreSQL 17 and 18.

Note

Fact. The measured inventory changes from 380 to 399 settings: 21 added, 5 boot-default changes, and 2 removed.

Added parameters

Parameter	Type	Context	Boot default	Category
`autovacuum_vacuum_max_threshold`	`integer`	`sighup`	`100000000`	Vacuuming / Automatic Vacuuming
`autovacuum_worker_slots`	`integer`	`postmaster`	`16`	Vacuuming / Automatic Vacuuming
`enable_distinct_reordering`	`bool`	`user`	`on`	Query Tuning / Planner Method Configuration
`enable_self_join_elimination`	`bool`	`user`	`on`	Query Tuning / Planner Method Configuration
`extension_control_path`	`string`	`superuser`	`$system`	Client Connection Defaults / Other Defaults
`file_copy_method`	`enum`	`user`	`copy`	Resource Usage / Disk
`idle_replication_slot_timeout`	`integer`	`sighup`	`0 s`	Replication / Sending Servers
`io_max_combine_limit`	`integer`	`postmaster`	`16 8kB` (128 KiB (16 × 8kB))	Resource Usage / I/O
`io_max_concurrency`	`integer`	`postmaster`	`-1`	Resource Usage / I/O
`io_method`	`enum`	`postmaster`	`worker`	Resource Usage / I/O
`io_workers`	`integer`	`sighup`	`3`	Resource Usage / I/O
`log_lock_failures`	`bool`	`superuser`	`off`	Reporting and Logging / What to Log
`max_active_replication_origins`	`integer`	`postmaster`	`10`	Replication / Subscribers
`md5_password_warnings`	`bool`	`user`	`on`	Connections and Authentication / Authentication
`num_os_semaphores`	`integer`	`internal`	`0`	Preset Options
`oauth_validator_libraries`	`string`	`sighup`	`""` (empty string)	Connections and Authentication / Authentication
`ssl_groups`	`string`	`sighup`	`X25519:prime256v1`	Connections and Authentication / SSL
`ssl_tls13_ciphers`	`string`	`sighup`	`""` (empty string)	Connections and Authentication / SSL
`track_cost_delay_timing`	`bool`	`superuser`	`off`	Statistics / Cumulative Query and Index Statistics
`vacuum_max_eager_freeze_failure_rate`	`real`	`user`	`0.03`	Vacuuming / Freezing
`vacuum_truncate`	`bool`	`user`	`on`	Vacuuming / Default Behavior

Boot-default changes

Parameter	PG17	PG18	Category
`effective_io_concurrency`	`1`	`16`	Resource Usage / I/O
`log_connections`	`off`	`""` (empty string)	Reporting and Logging / What to Log
`maintenance_io_concurrency`	`10`	`16`	Resource Usage / I/O
`server_version`	`17.11 (Debian 17.11-1.pgdg13+2)`	`18.6 (Debian 18.6-1.pgdg13+2)`	Preset Options
`server_version_num`	`170011`	`180006`	Preset Options

Removed parameters

Parameter	Last type	Context	Last boot default	Category
`extension_destdir`	`string`	`superuser`	`""` (empty string)	File Locations
`ssl_ecdh_curve`	`string`	`sighup`	`prime256v1`	Connections and Authentication / SSL

Method

The three lists compare the pinned PG17 and PG18 pg_settings snapshots directly. A default change is a change in the boot_val plus unit pair; setting is excluded so an initdb-generated value is not mistaken for the compiled boot default.