server: add postgresql initial configuration

modules/nixos/server/profiles/linode/postgresql.nix

@@ -0,0 +1,74 @@
+{
+  config,
+  lib,
+  ...
+}: let
+  inherit (lib) mkIf;
+  inherit (config.ooknet.server) database;
+in {
+  # hardware based postgresql configuration for: linode nano
+  # 4GB RAM 1 Core
+  # generated with: <http://pgconfigurator.cybertec.at>
+  config = mkIf database.postgresql {
+    services.postgresql = {
+      settings = {
+        # Connectivity
+        max_connections = 20;
+        superuser_reserved_connections = 3;
+
+        # Memory Settings
+        shared_buffers = "256 MB";
+        work_mem = "32 MB";
+        maintenance_work_mem = "320 MB";
+        huge_pages = "off";
+        effective_cache_size = "1 GB";
+        effective_io_concurrency = 100; # concurrent IO only really activated if OS supports posix_fadvise function
+        random_page_cost = 1.25; # speed of random disk access relative to sequential access (1.0)
+
+        # Monitoring
+        shared_preload_libraries = "pg_stat_statements"; # per statement resource usage stats
+        track_io_timing = "on"; # measure exact block IO times
+        track_functions = "pl"; # track execution times of pl-language procedures if any
+
+        # Replication
+        wal_level = "replica"; # consider using at least 'replica'
+        max_wal_senders = 0;
+        synchronous_commit = "on";
+
+        # Checkpointing:
+        checkpoint_timeout = "15 min";
+        checkpoint_completion_target = 0.9;
+        max_wal_size = "1024 MB";
+        min_wal_size = "512 MB";
+
+        # WAL writing
+        wal_compression = "on";
+        wal_buffers = -1; # auto-tuned by Postgres till maximum of segment size (16MB by default)
+        wal_writer_delay = "200ms";
+        wal_writer_flush_after = "1MB";
+
+        # Background writer
+        bgwriter_delay = "200ms";
+        bgwriter_lru_maxpages = 100;
+        bgwriter_lru_multiplier = 2.0;
+        bgwriter_flush_after = 0;
+
+        # Parallel queries:
+        max_worker_processes = 1;
+        max_parallel_workers_per_gather = 1;
+        max_parallel_maintenance_workers = 1;
+        max_parallel_workers = 1;
+        parallel_leader_participation = "on";
+
+        # Advanced features
+        enable_partitionwise_join = "on";
+        enable_partitionwise_aggregate = "on";
+        jit = "on";
+        max_slot_wal_keep_size = "1000 MB";
+        track_wal_io_timing = "on";
+        maintenance_io_concurrency = 100;
+        wal_recycle = "on";
+      };
+    };
+  };
+}