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PostgreSQL 查看表膨胀情况的方法
表膨胀(Table Bloat)是PostgreSQL中由于MVCC机制导致的一种常见现象，当大量数据被更新或删除后，表中会积累"死元组"(dead tuples)，这些死元组占据空间但不可见，导致表实际占用的磁盘空间远大于有效数据所需空间。
使用内置视图查看表膨胀
1 使用 pg_stat_user_tables 视图
SELECTschemaname || '.' || relname AS table_name,pg_size_pretty(pg_total_relation_size(relid)) AS total_size,pg_size_pretty(pg_relation_size(relid)) AS data_size,n_live_tup AS live_tuples,n_dead_tup AS dead_tuples,round((n_dead_tup::numeric / (n_live_tup + n_dead_tup) * 100), 2) AS dead_tuple_percent,last_vacuum,last_autovacuum
FROM pg_stat_user_tables
WHERE n_live_tup > 0
ORDER BY dead_tuple_percent DESC;
输出示例：
table_name | total_size | data_size | live_tuples | dead_tuples | dead_tuple_percent | last_vacuum | last_autovacuum
--------------+------------+------------+-------------+-------------+--------------------+----------------------------+-------------------------------yewu1.t3 | 8192 bytes | 8192 bytes | 10 | 90 | 90.00 | | 2025-04-04 00:59:57.62698-07yewu1.t1 | 712 kB | 440 kB | 10000 | 0 | 0.00 | 2025-05-02 00:09:40.147-07 | 2025-04-03 16:43:51.808336-07yewu1.test10 | 8192 bytes | 8192 bytes | 4 | 0 | 0.00 | | yewu1.t2 | 472 kB | 440 kB | 10000 | 0 | 0.00 | | 2025-04-03 16:46:51.858759-07
(4 rows)
2. 使用 pgstattuple 扩展获取详细膨胀数据
-- 先创建扩展
CREATE EXTENSION IF NOT EXISTS pgstattuple;-- 查看特定表的膨胀情况
SELECT * FROM pgstattuple('schema_name.table_name');-- 估算所有表的膨胀情况
SELECTschemaname || '.' || relname AS table,(pgstattuple(schemaname || '.' || relname)).*
FROM pg_stat_user_tables;
输出示例：
table | table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_
percent
-------------------------+-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+------
--------yewu1.t1 | 450560 | 10000 | 378894 | 84.09 | 0 | 0 | 0 | 9020 | 2yewu1.t2 | 450560 | 10000 | 378894 | 84.09 | 0 | 0 | 0 | 9020 | 2public.pgbench_history | 14024704 | 267227 | 12826896 | 91.46 | 0 | 0 | 0 | 7488 | 0.05yewu1.test1 | 8192 | 3 | 161 | 1.97 | 0 | 0 | 0 | 7984 | 97.46yewu1.test6 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0public.pgbench_tellers | 8192 | 100 | 3600 | 43.95 | 0 | 0 | 0 | 3764 | 45.95yewu2.t4 | 8192 | 1 | 28 | 0.34 | 0 | 0 | 0 | 8128 | 99.22yewu1.test5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0public.pgbench_branches | 8192 | 10 | 320 | 3.91 | 0 | 0 | 0 | 7804 | 95.26yewu1.test7 | 513892352 | 10000000 | 408888897 | 79.57 | 0 | 0 | 0 | 135876 | 0.03yewu1.test3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0yewu1.test2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0yewu1.t3 | 8192 | 10 | 351 | 4.28 | 90 | 3241 | 39.56 | 3764 | 45.95public.pgbench_accounts | 134479872 | 1000000 | 121000000 | 89.98 | 0 | 0 | 0 | 1840616 | 1.37yewu1.test10 | 8192 | 4 | 136 | 1.66 | 0 | 0 | 0 | 7988 | 97.51yewu1.test4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0yewu1.test8 | 513892352 | 10000000 | 408888897 | 79.57 | 0 | 0 | 0 | 135876 | 0.03
(17 rows)