PostgreSQLの設定は多くの異なる方法で設定することができます。 しかし普通はpostgresql.confファイルで設定することになるでしょう。 固有のオプションはリリースごとに異なります。 使用中のPostgreSQLのsrc/backend/utils/misc/guc.cというソースコードに利用可能なリストがあります。 （しかし普通はpg_settingsビューを参照することで十分だと思います。）
Tuning Your PostgreSQL Server/ja - PostgreSQL wiki
- pg_settings ビューで確認する
$ psql "host=aurora-postgres124.cluster-********.ap-northeast-1.rds.amazonaws.com user=awsuser dbname=postgres port=5432" psql (13.4, server 12.4) SSL connection (protocol: TLSv1.2, cipher: ECDHE-RSA-AES256-GCM-SHA384, bits: 256, compression: off) Type "help" for help. postgres=> \pset pager Pager usage is off. postgres=> select name from pg_settings; name ------------------------------------------ allow_system_table_mods ansi_constraint_trigger_ordering ansi_force_foreign_key_checks ansi_qualified_update_set_target apg_buffer_invalid_lookup_strategy apg_enable_batch_mode_function_execution apg_enable_correlated_any_transform apg_enable_function_migration apg_enable_not_in_transform apg_enable_remove_redundant_inner_joins apg_enable_semijoin_push_down apg_force_full_key_semijoin apg_force_semijoin_push_down apg_force_single_key_semijoin application_name archive_cleanup_command archive_command archive_mode archive_timeout array_nulls async_notifications_cache_size authentication_timeout autovacuum autovacuum_analyze_scale_factor autovacuum_analyze_threshold autovacuum_freeze_max_age autovacuum_max_workers autovacuum_multixact_freeze_max_age autovacuum_naptime autovacuum_vacuum_cost_delay autovacuum_vacuum_cost_limit autovacuum_vacuum_scale_factor autovacuum_vacuum_threshold autovacuum_work_mem backend_flush_after backslash_quote bgwriter_delay bgwriter_flush_after bgwriter_lru_maxpages bgwriter_lru_multiplier block_size bonjour bonjour_name bytea_output check_function_bodies checkpoint_completion_target checkpoint_flush_after checkpoint_timeout checkpoint_warning client_encoding client_min_messages cluster_name commit_delay commit_siblings commit_timestamp_cache_size config_file constraint_exclusion cpu_index_tuple_cost cpu_operator_cost cpu_tuple_cost cursor_tuple_fraction data_checksums data_directory data_directory_mode data_sync_retry DateStyle db_user_namespace deadlock_timeout debug_assertions debug_pretty_print debug_print_parse debug_print_plan debug_print_rewritten default_statistics_target default_table_access_method default_tablespace default_text_search_config default_transaction_deferrable default_transaction_isolation default_transaction_read_only dynamic_library_path dynamic_shared_memory_type effective_cache_size effective_io_concurrency enable_bitmapscan enable_gathermerge enable_hashagg enable_hashjoin enable_indexonlyscan enable_indexscan enable_material enable_mergejoin enable_nestloop enable_parallel_append enable_parallel_hash enable_partition_pruning enable_partitionwise_aggregate enable_partitionwise_join enable_seqscan enable_sort enable_tidscan escape_string_warning event_source eventpoints_mode exit_on_error external_pid_file extra_float_digits force_parallel_mode from_collapse_limit fsync full_page_writes geqo geqo_effort geqo_generations geqo_pool_size geqo_seed geqo_selection_bias geqo_threshold gin_fuzzy_search_limit gin_pending_list_limit hba_file hot_standby hot_standby_feedback huge_pages ident_file idle_in_transaction_session_timeout ignore_checksum_failure ignore_system_indexes integer_datetimes IntervalStyle jit jit_above_cost jit_debugging_support jit_dump_bitcode jit_expressions jit_inline_above_cost jit_optimize_above_cost jit_profiling_support jit_provider jit_tuple_deforming join_collapse_limit krb_caseins_users krb_server_keyfile lc_collate lc_ctype lc_messages lc_monetary lc_numeric lc_time listen_addresses lo_compat_privileges local_preload_libraries lock_timeout log_autovacuum_min_duration log_checkpoints log_connections log_destination log_directory log_disconnections log_duration log_error_verbosity log_executor_stats log_file_mode log_filename log_hostname log_line_prefix log_lock_waits log_min_duration_statement log_min_error_statement log_min_messages log_parser_stats log_planner_stats log_replication_commands log_rotation_age log_rotation_size log_statement log_statement_stats log_temp_files log_timezone log_transaction_sample_rate log_truncate_on_rotation logging_collector logical_decoding_work_mem maintenance_work_mem max_connections max_files_per_process max_function_args max_identifier_length max_index_keys max_locks_per_transaction max_logical_replication_workers max_parallel_maintenance_workers max_parallel_workers max_parallel_workers_per_gather max_pred_locks_per_page max_pred_locks_per_relation max_pred_locks_per_transaction max_prepared_transactions max_replication_slots max_stack_depth max_standby_archive_delay max_standby_streaming_delay max_sync_workers_per_subscription max_wal_senders max_wal_size max_worker_processes min_parallel_index_scan_size min_parallel_table_scan_size min_wal_size multixact_members_cache_size multixact_offsets_cache_size old_snapshot_threshold operator_precedence_warning parallel_leader_participation parallel_setup_cost parallel_tuple_cost password_encryption pg_stat_statements.max pg_stat_statements.save pg_stat_statements.track pg_stat_statements.track_utility plan_cache_mode port post_auth_delay pre_auth_delay primary_conninfo primary_slot_name promote_trigger_file quote_all_identifiers random_page_cost rds.enable_global_db_rpo rds.extensions rds.force_admin_logging_level rds.force_autovacuum_logging_level rds.global_db_rpo rds.internal_databases rds.logical_replication rds.rds_superuser_reserved_connections rds.restrict_logical_slot_creation rds.restrict_password_commands rds.superuser_variables rds.tablespace_path_prefix recovery_end_command recovery_min_apply_delay recovery_target recovery_target_action recovery_target_inclusive recovery_target_lsn recovery_target_name recovery_target_time recovery_target_timeline recovery_target_xid restart_after_crash restore_command row_security search_path segment_size seq_page_cost server_encoding server_version server_version_num session_preload_libraries session_replication_role shared_buffers shared_memory_type shared_preload_libraries slru_cache_mode ssl ssl_ca_file ssl_cert_file ssl_ciphers ssl_crl_file ssl_dh_params_file ssl_ecdh_curve ssl_key_file ssl_library ssl_max_protocol_version ssl_max_protocol_version ssl_min_protocol_version ssl_min_protocol_version ssl_passphrase_command ssl_passphrase_command_supports_reload ssl_prefer_server_ciphers standard_conforming_strings statement_timeout stats_temp_directory subtrans_cache_size superuser_reserved_connections survivable_cache_mode synchronize_seqscans synchronous_commit synchronous_standby_names syslog_facility syslog_ident syslog_sequence_numbers syslog_split_messages tcp_keepalives_count tcp_keepalives_idle tcp_keepalives_interval tcp_user_timeout temp_buffers temp_file_limit temp_tablespaces TimeZone timezone_abbreviations trace_notify trace_recovery_messages trace_sort track_activities track_activity_query_size track_commit_timestamp track_counts track_functions track_io_timing transaction_deferrable transaction_isolation transaction_read_only transform_null_equals unix_socket_directories unix_socket_group unix_socket_permissions update_process_title vacuum_cleanup_index_scale_factor vacuum_cost_delay vacuum_cost_limit vacuum_cost_page_dirty vacuum_cost_page_hit vacuum_cost_page_miss vacuum_defer_cleanup_age vacuum_freeze_min_age vacuum_freeze_table_age vacuum_multixact_freeze_min_age vacuum_multixact_freeze_table_age wal_block_size wal_buffers wal_compression wal_consistency_checking wal_init_zero wal_keep_segments wal_level wal_log_hints wal_receiver_status_interval wal_receiver_timeout wal_recycle wal_retrieve_retry_interval wal_segment_size wal_sender_timeout wal_sync_method wal_writer_delay wal_writer_flush_after work_mem xmlbinary xmloption zero_damaged_pages (354 rows)
参考
PostgreSQLのソースコードの構造
パス 内容 src/backend/utils その他色々なコード（設定パラメータ、カタログキャッシュ、メモリ管理、各データ型の実装など）
