【PostgreSQL如何查看page、index的详细信息】
一、创建插件
为了更好地查看page页的内容，需要安装两个插件
create extension pgstatuple
create extension pageinspect
二、相关函数举例
1.查看表占用多少个page
postgres=# select * from pg_relpages( 't' );
pg_relpages
-------------
54055
(1 row)
2.查看一个表的tuple信息
postgres=# select * from pgstattuple('t');
-[ RECORD 1 ]------+----------
table_len | 765607936
tuple_count | 10000000
tuple_len | 720000000
tuple_percent | 94.04
dead_tuple_count | 0
dead_tuple_len | 0
dead_tuple_percent | 0
free_space | 2991112
free_percent | 0.39
3.查看一个表上的索引信息
select * from pgstatindex('t');
-[ RECORD 1 ]------+---------
version | 4
tree_level | 2
index_size | 22487040
root_block_no | 412
internal_pages | 11
leaf_pages | 2733
empty_pages | 0
deleted_pages | 0
avg_leaf_density | 90.06
leaf_fragmentation | 0
4.查看表t的第0号页的页头信息
select * from page_header(get_raw_page(relname text, 'main', page number));
=====>>eg.
postgres=# select * from page_header(get_raw_page('t','main',0));
lsn | checksum | flags | lower | upper | special | pagesize | version | prune_xid
------------+----------+-------+-------+-------+---------+----------+---------+-----------
1/51015D20 | 29528 | 1 | 776 | 792 | 8192 | 8192 | 4 | 1689
(1 row)
5.查看表t的第0号页中行数据相关信息
SELECT * FROM heap_page_items(get_raw_page(relname text,page number));
=====>>eg.
postgres=# SELECT * FROM heap_page_items(get_raw_page('t',0));
lp | lp_off | lp_flags | lp_len | t_xmin | t_xmax | t_field3 | t_ctid | t_infomask2 | t_infomask | t_hoff | t_bits | t_oid | t_data
-----+--------+----------+--------+--------+--------+----------+---------+-------------+------------+--------+--------+-------+----------------------------
1 | 16 | 2 | 0 | | | | | | | | | |
2 | 832 | 1 | 36 | 1685 | 0 | 0 | (0,2) | 2 | 2050 | 24 | | | \x0f7570646174650030010000
3 | 2032 | 1 | 36 | 1665 | 0 | 0 | (0,3) | 2 | 2306 | 24 | | | \x0f757064617465002d010000
4 | 8112 | 1 | 36 | 1655 | 0 | 0 | (0,4) | 2 | 2306 | 24 | | | \x0f7570646174650058010000
5 | 8072 | 1 | 36 | 1655 | 0 | 0 | (0,5) | 2 | 2306 | 24 | | | \x0f7570646174650059010000
6 | 8032 | 1 | 36 | 1655 | 0 | 0 | (0,6) | 2 | 2306 | 24 | | | \x0f757064617465005a010000
6.查看一个B树索引元页的信息
select * from bt_metap(relname text);
=====>>eg.
postgres=# select * from bt_metap('t');
-[ RECORD 1 ]-----------+-------
magic | 340322
version | 4
root | 1
level | 0
fastroot | 1
fastlevel | 0
oldest_xact | 0
last_cleanup_num_tuples | 3
7.查看B-树索引单一页面的摘要信息
select * from bt_page_stats(relname text, page number)
=====>>eg.
postgres=# SELECT * FROM bt_page_stats('t', 1);
-[ RECORD 1 ]-+-----
blkno | 1
type | l
live_items | 256
dead_items | 0
avg_item_size | 12
page_size | 8192
free_size | 4056
btpo_prev | 0
btpo_next | 0
btpo | 0
btpo_flags | 3
8.查看关于B-树索引页面上所有项的详细信息
select * from bt_page_items(relname text, page number)
=====>>eg.
test=# SELECT * FROM bt_page_items('pg_cast_oid_index', 1);
itemoffset | ctid | itemlen | nulls | vars | data
------------+---------+---------+-------+------+-------------
1 | (0,1) | 12 | f | f | 23 27 00 00
2 | (0,2) | 12 | f | f | 24 27 00 00
3 | (0,3) | 12 | f | f | 25 27 00 00
4 | (0,4) | 12 | f | f | 26 27 00 00
5 | (0,5) | 12 | f | f | 27 27 00 00
6 | (0,6) | 12 | f | f | 28 27 00 00
7 | (0,7) | 12 | f | f | 29 27 00 00
8 | (0,8) | 12 | f | f | 2a 27 00 00
9.查看database 所有的含有需要toast子段的table
select t1.relid, t1.schemaname, t1.relname, t2.relid, t2.schemaname, t2.relname from pg_stat_all_tables t1 inner join pg_stat_all_tables t2 on 'pg_toast_'|| t1.relid = t2.relname and t1.schemaname = 'public'
=====>>eg.
postgres=# select t1.relid, t1.schemaname, t1.relname, t2.relid, t2.schemaname, t2.relname from pg_stat_all_tables t1 inner join pg_stat_all_tables t2 on 'pg_toast_'|| t1.relid = t2.relname and t1.schemaname = 'public';
relid | schemaname | relname | relid | schemaname | relname
-------+------------+--------------------------------------+-------+------------+----------------
33222 | public | datahub_fact_scm_materialgeneral | 33225 | pg_toast | pg_toast_33222
33229 | public | etl_errorlog | 33232 | pg_toast | pg_toast_33229
16395 | public | test | 32781 | pg_toast | pg_toast_16395
33216 | public | datahub_fact_scm_materialgeneral_etl | 33220 | pg_toast | pg_toast_33216
(4 rows)
10.查看FSM页面的内部节点结构，查看free space map的信息。
select * from fsm_page_contents(page bytea) returns text
=====>>eg.
SELECT fsm_page_contents(get_raw_page('t', 'fsm', 0));
fsm_page_contents
-------------------
0: 251 +
1: 251 +
3: 251 +
7: 251 +
15: 251 +
31: 251 +
63: 251 +
127: 251 +
255: 251 +
511: 251 +
1023: 251 +
2047: 251 +
4095: 251 +
8191: 251 +
16383: 251 +
fp_next_slot: 0 +
(1 row)