目录
pg_aggregatepg_ampg_amoppg_amprocpg_attrdefpg_attributepg_authidpg_auth_memberspg_castpg_classpg_collationpg_constraintpg_conversionpg_databasepg_db_role_settingpg_default_aclpg_dependpg_descriptionpg_enumpg_event_triggerpg_extensionpg_foreign_data_wrapperpg_foreign_serverpg_foreign_tablepg_indexpg_inheritspg_init_privspg_languagepg_largeobjectpg_largeobject_metadatapg_namespacepg_opclasspg_operatorpg_opfamilypg_partitioned_tablepg_policypg_procpg_publicationpg_publication_relpg_rangepg_replication_originpg_rewritepg_seclabelpg_sequencepg_shdependpg_shdescriptionpg_shseclabelpg_statisticpg_statistic_extpg_statistic_ext_datapg_subscriptionpg_subscription_relpg_tablespacepg_transformpg_triggerpg_ts_configpg_ts_config_mappg_ts_dictpg_ts_parserpg_ts_templatepg_typepg_user_mappingpg_available_extensionspg_available_extension_versionspg_backend_memory_contextspg_configpg_cursorspg_file_settingspg_grouppg_hba_file_rulespg_indexespg_lockspg_matviewspg_policiespg_prepared_statementspg_prepared_xactspg_publication_tablespg_replication_origin_statuspg_replication_slotspg_rolespg_rulespg_seclabelspg_sequencespg_settingspg_shadowpg_shmem_allocationspg_statspg_stats_extpg_stats_ext_exprspg_tablespg_timezone_abbrevspg_timezone_namespg_userpg_user_mappingspg_views
系统目录是关系型数据库存放模式元数据的地方，比如表和列的信息，以及内部统计信息等。PostgreSQL的系统目录就是普通表。你可以删除并重建这些表、增加列、插入和更新数值， 然后彻底把你的系统搞垮。 通常情况下，我们不应该手工修改系统目录，通常有SQL命令可以做这些事情。（例如，CREATE DATABASE向 pg_database表插入一行 — 并且实际上在磁盘上创建该数据库。）。 有几种特别深奥的操作例外，但是随着时间的流逝其中的很多也可以用 SQL 命令来完成，因此对系统目录直接修改的需求也越来越小。