Postgresql 系统相关函数介绍
Postgresql xlog
先看下pg_xlog下物理文件的命名，大小在数据库编译安装的时候-with-wal-segsize指定
000000010000000200000019
XLogFileName宏里定义的，分别由时间线ID、日志ID、段ID的八位16进制数依次构成
日志ID最大为0xFFFFFFFFF，段ID最大为0x000000F
相关函数：
pg_current_xlog_insert_location() 获取写入wal buffer的事物号
pg_current_xlog_location() 获取写入wal日志的事物号
postgres=# select pg_current_xlog_location(),pg_current_xlog_insert_location();
pg_current_xlog_location | pg_current_xlog_insert_location
--------------------------+---------------------------------
3C64/2EAC2000 | 3C64/2EAC2780
可以看到写入buffer是要早于写入wal日志的
pg_xlogfile_name() 把事务日志的位置字符串转换为文件名
postgres=# select pg_xlogfile_name('3C64/2EACBD08');
pg_xlogfile_name
--------------------------
0000000300003C640000000B
pg_xlogfile_name_offset() 把事务日志的位置字符串转换为文件名和文件内部十进制字节的偏移量
postgres=# select pg_xlogfile_name_offset('3C64/2EACBD08');
pg_xlogfile_name_offset
-------------------------------------
(0000000300003C640000000B,44875016)
可以通过以下语句查看插入buffer的位置和最后发送到standby节点的事物相差多少，是否有长时间的延迟
select pg_xlog_location_diff(pg_current_xlog_insert_location(),sent_location) from pg_stat_replication;
| Name | Return Type | Description |
|---|---|---|
| current_setting(setting_name) | text | 获取当前参数值 |
| set_config(setting_name, new_value, is_local) | text | 设置新的参数值 |
| Name | Return Type | Description |
|---|---|---|
| pg_cancel_backend(pidint) | boolean | Cancel a backend's current query. You can execute this against another backend that has exactly the same role as the user calling the function. In all other cases, you must be a superuser. |
| pg_reload_conf() | boolean | Cause server processes to reload their configuration files |
| pg_rotate_logfile() | boolean | Rotate server's log file |
| pg_terminate_backend(pidint) | boolean | Terminate a backend. You can execute this against another backend that has exactly the same role as the user calling the function. In all other cases, you must be a superuser. |
| Name |
Return Type | Description |
|---|---|---|
| pg_create_restore_point(name text) | pg_lsn | Create a named point for performing restore (restricted to superusers) |
| pg_current_xlog_insert_location() | pg_lsn | 获取写入wal buffer的事物号 |
| pg_current_xlog_location() | pg_lsn | 获取写入wal日志的事物号 |
| pg_start_backup(label text [, fast boolean ]) | pg_lsn | 主备在线备份开始 |
| pg_stop_backup() | pg_lsn | 在线备份结束 |
| pg_is_in_backup() | bool | 如果返回true，说明正在线备份 |
| pg_backup_start_time() | timestamp with time zone | 获取在线备份的开始时间 |
| pg_switch_xlog() | pg_lsn | 强制切换到新的事物日志 |
| pg_xlogfile_name(location pg_lsn) | text | 转换事物号为文件名 |
| pg_xlogfile_name_offset(location pg_lsn) |
text, integer | 转换事物号为文件名，并带有十进制字节偏移量 |
| pg_xlog_location_diff(location pg_lsn, location pg_lsn) | numeric | 计算两个事物之间的相差多少字节 |
| Name | Return Type | Description |
|---|---|---|
| pg_is_in_recovery() | bool | 如果返回true，说明在做recovery，流复制环境也就是说是备节点 |
| pg_last_xlog_receive_location() | pg_lsn | Get last transaction log location received and synced to disk by streaming replication. While streaming replication is in progress this will increase monotonically. If recovery has completed this will remain static at the value of the last WAL record received and synced to disk during recovery.If streaming replication is disabled, or if it has not yet started, the function returns NULL. |
| pg_last_xlog_replay_location() | pg_lsn | Get last transaction log location replayed during recovery. If recovery is still in progress this will increase monotonically. If recovery has completed then this value will remain static at the value of the last WAL record applied during that recovery. When the server has been started normally without recovery the function returns NULL. |
| pg_last_xact_replay_timestamp() | timestamp with time zone | Get time stamp of last transaction replayed during recovery. This is the time at which the commit or abort WAL record for that transaction was generated on the primary. If no transactions have been replayed during recovery, this function returns NULL. Otherwise, if recovery is still in progress this will increase monotonically. If recovery has completed then this value will remain static at the value of the last transaction applied during that recovery. When the server has been started normally without recovery the function returns NULL. |
| Name | Return Type | Description |
|---|---|---|
| pg_is_xlog_replay_paused() | bool | 如果recovery被暂停，那么这个函数返回true |
| pg_xlog_replay_pause() | void | 暂停recovery |
| pg_xlog_replay_resume() | void | 暂停后重新recovery |
数据库对象大小查询函数
| Name | Return Type | Description |
|---|---|---|
| pg_column_size(any) | int | 查询列字节数 |
| pg_database_size(oid) | bigint | 通过OID查询数据库大小 |
| pg_database_size(name) | bigint | 通过数据库名称查询数据库大小 |
| pg_indexes_size(regclass) | bigint | 查询指定索引大小 |
| pg_relation_size(relation regclass, fork text) | bigint | Disk space used by the specified fork ('main', 'fsm', 'vm', or 'init') of the specified table or index |
| pg_relation_size(relation regclass) | bigint | Shorthand for pg_relation_size(..., 'main') |
| pg_size_pretty(bigint) | text | 格式化为64bit人类易读的形式 |
| pg_size_pretty(numeric) | text | 同上，只是格式化为numeric类型 |
| pg_table_size(regclass) | bigint | 查询指定表的大小，不包括索引，（但是包括 TOAST, free space map, and visibility map) |
| pg_tablespace_size(oid) | bigint | 通过oid查询指定表空间的大小 |
| pg_tablespace_size(name) | bigint | 通过空间名称查询指定表空间大小 |
| pg_total_relation_size(regclass) | bigint | 查询包括表的大小以及索引的大小，并且包括TOAST数据 |
数据库对象物理位置函数
| Name | Return Type | Description |
|---|---|---|
| pg_relation_filenode(relation regclass) | oid | 返回数据对象的filenode |
| pg_relation_filepath(relation regclass) | text | 返回数据对象的文件路径 |
| pg_filenode_relation(tablespace oid, filenode oid) | regclass | 通过给tablespace oid，以及filenode返回表名称 |
hank=> select pg_relation_filenode('t1');
pg_relation_filenode
----------------------
21865
(1 row)
hank=> select pg_relation_filepath('t1');
pg_relation_filepath
----------------------------------------------
pg_tblspc/21862/PG_9.4_201409291/21863/21865
hank=> select oid,* from pg_tablespace;
oid | spcname | spcowner | spcacl | spcoptions
-------+------------+----------+---------------------------------------+------------
1663 | pg_default | 10 | |
1664 | pg_global | 10 | |
21862 | tbs_hank | 10 | {postgres=C/postgres,hank=C/postgres} |
hank=> select pg_filenode_relation(21862,21865);
pg_filenode_relation
----------------------
t1
(1 row)
这里只介绍了部分常用的系统函数，对部分函数做了实例
参考：http://www.postgresql.org/docs/9.4/static/functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE