获取分区 table 的 table 大小（Postgres 10+）

Question

我在 Postgres weekly 上遇到了这个查询，它以字节为单位显示了 tables、它们的大小、toast 大小和索引大小：

SELECT
  relname AS table_name,
  pg_size_pretty(pg_total_relation_size(relid)) AS total,
  pg_size_pretty(pg_relation_size(relid)) AS internal,
  pg_size_pretty(pg_table_size(relid) - pg_relation_size(relid)) AS external,
  pg_size_pretty(pg_indexes_size(relid)) AS indexes
FROM pg_catalog.pg_statio_user_tables 
ORDER BY pg_total_relation_size(relid) DESC;

我知道 Postgres 正在为每个分区创建一个 table，所以我分别为每个分区获取条目，但是有没有办法为每个 table 获取一行，而不管这是否table是否分区？

Answer 1

当然可以，但是您必须加入一堆其他目录 table 并使用 GROUP BY。

目录 pg_class 中的属性 relkind 将告诉您关系是否已分区 (p) 或未分区 (r)。
目录pg_inherits会告诉你哪个分区(inhrelid)属于哪个分区table(inhparent).

因为分区可以再分区，所以要覆盖所有的基就得写一个递归的通用table表达式

Answer 2

按照@Laurenz Albe 的说明，我创建了一个满足我需求的查询。这将从特定数据库中获取所有分区 table 的总内存。

SELECT
   pi.inhparent::regclass AS parent_table_name, 
   pg_size_pretty(sum(pg_total_relation_size(psu.relid))) AS total,
   pg_size_pretty(sum(pg_relation_size(psu.relid))) AS internal,
   pg_size_pretty(sum(pg_table_size(psu.relid) - pg_relation_size(psu.relid))) AS external, -- toast
   pg_size_pretty(sum(pg_indexes_size(psu.relid))) AS indexes
FROM pg_catalog.pg_statio_user_tables psu
   JOIN pg_class pc ON psu.relname = pc.relname
   JOIN pg_database pd ON pc.relowner = pd.datdba
   JOIN pg_inherits pi ON pi.inhrelid = pc.oid
WHERE pd.datname = :database_name
GROUP BY pi.inhparent
ORDER BY sum(pg_total_relation_size(psu.relid)) DESC;

请注意，在我们有多个分区的情况下，根 table 不会有一行，但每个父 table 都会有自己的行

Answer 3

即使我们有多个分区级别，这也会为每个父级 table 提供 table 大小：

WITH RECURSIVE tables AS (
  SELECT
    c.oid AS parent,
    c.oid AS relid,
    1     AS level
  FROM pg_catalog.pg_class c
  LEFT JOIN pg_catalog.pg_inherits AS i ON c.oid = i.inhrelid
    -- p = partitioned table, r = normal table
  WHERE c.relkind IN ('p', 'r')
    -- not having a parent table -> we only get the partition heads
    AND i.inhrelid IS NULL
  UNION ALL
  SELECT
    p.parent         AS parent,
    c.oid            AS relid,
    p.level + 1      AS level
  FROM tables AS p
  LEFT JOIN pg_catalog.pg_inherits AS i ON p.relid = i.inhparent
  LEFT JOIN pg_catalog.pg_class AS c ON c.oid = i.inhrelid AND c.relispartition
  WHERE c.oid IS NOT NULL
)
SELECT
  parent ::REGCLASS                                  AS table_name,
  array_agg(relid :: REGCLASS)                       AS all_partitions,
  pg_size_pretty(sum(pg_total_relation_size(relid))) AS pretty_total_size,
  sum(pg_total_relation_size(relid))                 AS total_size
FROM tables
GROUP BY parent
ORDER BY sum(pg_total_relation_size(relid)) DESC

获取分区 table 的 table 大小（Postgres 10+）

Get table size of partitioned table (Postgres 10+)

postgresql

postgresql-10

postgresql-11

postgres-12