PostgreSQL queries

Disk usage

Most of these queries vary based on the database you are connected to.

General Table Size Information Grouped For Partitioned Tables 

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WITH RECURSIVE pg_inherit(inhrelid, inhparent) AS
    (select inhrelid, inhparent
    FROM pg_inherits
    UNION
    SELECT child.inhrelid, parent.inhparent
    FROM pg_inherit child, pg_inherits parent
    WHERE child.inhparent = parent.inhrelid),
pg_inherit_short AS (SELECT * FROM pg_inherit WHERE inhparent NOT IN (SELECT inhrelid FROM pg_inherit))
SELECT table_schema
    , TABLE_NAME
    , row_estimate
    , pg_size_pretty(total_bytes) AS total
    , pg_size_pretty(index_bytes) AS INDEX
    , pg_size_pretty(toast_bytes) AS toast
    , pg_size_pretty(table_bytes) AS TABLE
  FROM (
    SELECT *, total_bytes-index_bytes-COALESCE(toast_bytes,0) AS table_bytes
    FROM (
         SELECT c.oid
              , nspname AS table_schema
              , relname AS TABLE_NAME
              , SUM(c.reltuples) OVER (partition BY parent) AS row_estimate
              , SUM(pg_total_relation_size(c.oid)) OVER (partition BY parent) AS total_bytes
              , SUM(pg_indexes_size(c.oid)) OVER (partition BY parent) AS index_bytes
              , SUM(pg_total_relation_size(reltoastrelid)) OVER (partition BY parent) AS toast_bytes
              , parent
          FROM (
                SELECT pg_class.oid
                    , reltuples
                    , relname
                    , relnamespace
                    , pg_class.reltoastrelid
                    , COALESCE(inhparent, pg_class.oid) parent
                FROM pg_class
                    LEFT JOIN pg_inherit_short ON inhrelid = oid
                WHERE relkind IN ('r', 'p')
             ) c
             LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
  ) a
  WHERE oid = parent
) a
ORDER BY total_bytes DESC;

General Table Size Information 

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SELECT *, pg_size_pretty(total_bytes) AS total
    , pg_size_pretty(index_bytes) AS index
    , pg_size_pretty(toast_bytes) AS toast
    , pg_size_pretty(table_bytes) AS table
  FROM (
  SELECT *, total_bytes-index_bytes-coalesce(toast_bytes,0) AS table_bytes FROM (
      SELECT c.oid,nspname AS table_schema, relname AS table_name
              , c.reltuples AS row_estimate
              , pg_total_relation_size(c.oid) AS total_bytes
              , pg_indexes_size(c.oid) AS index_bytes
              , pg_total_relation_size(reltoastrelid) AS toast_bytes
          FROM pg_class c
          LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
          WHERE relkind = 'r'
  ) a
) a;

Finding the largest databases in your cluster 

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SELECT d.datname as Name,  pg_catalog.pg_get_userbyid(d.datdba) as Owner,
    CASE WHEN pg_catalog.has_database_privilege(d.datname, 'CONNECT')
        THEN pg_catalog.pg_size_pretty(pg_catalog.pg_database_size(d.datname))
        ELSE 'No Access'
    END as Size
FROM pg_catalog.pg_database d
    order by
    CASE WHEN pg_catalog.has_database_privilege(d.datname, 'CONNECT')
        THEN pg_catalog.pg_database_size(d.datname)
        ELSE NULL
    END desc -- nulls first
    LIMIT 20;

Finding the size of your biggest relations

Relations are objects in the database such as tables and indexes, and this query shows the size of all the individual parts.

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SELECT nspname || '.' || relname AS "relation",
    pg_size_pretty(pg_relation_size(C.oid)) AS "size"
  FROM pg_class C
  LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
  WHERE nspname NOT IN ('pg_catalog', 'information_schema')
  ORDER BY pg_relation_size(C.oid) DESC
  LIMIT 20;

Finding the total size of your biggest tables 

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SELECT nspname || '.' || relname AS "relation",
    pg_size_pretty(pg_total_relation_size(C.oid)) AS "total_size"
  FROM pg_class C
  LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
  WHERE nspname NOT IN ('pg_catalog', 'information_schema')
    AND C.relkind <> 'i'
    AND nspname !~ '^pg_toast'
  ORDER BY pg_total_relation_size(C.oid) DESC
  LIMIT 20;

Indexes

Index summary 

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SELECT
    pg_class.relname,
    pg_size_pretty(pg_class.reltuples::bigint) AS rows_in_bytes,
    pg_class.reltuples AS num_rows,
    count(indexname) AS number_of_indexes,
    CASE WHEN x.is_unique = 1 THEN 'Y'
       ELSE 'N'
    END AS UNIQUE,
    SUM(case WHEN number_of_columns = 1 THEN 1
              ELSE 0
            END) AS single_column,
    SUM(case WHEN number_of_columns IS NULL THEN 0
             WHEN number_of_columns = 1 THEN 0
             ELSE 1
           END) AS multi_column
FROM pg_namespace 
LEFT OUTER JOIN pg_class ON pg_namespace.oid = pg_class.relnamespace
LEFT OUTER JOIN
       (SELECT indrelid,
           max(CAST(indisunique AS integer)) AS is_unique
       FROM pg_index
       GROUP BY indrelid) x
       ON pg_class.oid = x.indrelid
LEFT OUTER JOIN
    ( SELECT c.relname AS ctablename, ipg.relname AS indexname, x.indnatts AS number_of_columns FROM pg_index x
           JOIN pg_class c ON c.oid = x.indrelid
           JOIN pg_class ipg ON ipg.oid = x.indexrelid  )
    AS foo
    ON pg_class.relname = foo.ctablename
WHERE 
     pg_namespace.nspname='public'
AND  pg_class.relkind = 'r'
GROUP BY pg_class.relname, pg_class.reltuples, x.is_unique
ORDER BY 2;

Index size/usage statistics 

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SELECT
    t.schemaname,
    t.tablename,
    indexname,
    c.reltuples AS num_rows,
    pg_size_pretty(pg_relation_size(quote_ident(t.schemaname)::text || '.' || quote_ident(t.tablename)::text)) AS table_size,
    pg_size_pretty(pg_relation_size(quote_ident(t.schemaname)::text || '.' || quote_ident(indexrelname)::text)) AS index_size,
    CASE WHEN indisunique THEN 'Y'
        ELSE 'N'
    END AS UNIQUE,
    number_of_scans,
    tuples_read,
    tuples_fetched
FROM pg_tables t
LEFT OUTER JOIN pg_class c ON t.tablename = c.relname
LEFT OUTER JOIN (
    SELECT
        c.relname AS ctablename,
        ipg.relname AS indexname,
        x.indnatts AS number_of_columns,
        idx_scan AS number_of_scans,
        idx_tup_read AS tuples_read,
        idx_tup_fetch AS tuples_fetched,
        indexrelname,
        indisunique,
        schemaname
    FROM pg_index x
    JOIN pg_class c ON c.oid = x.indrelid
    JOIN pg_class ipg ON ipg.oid = x.indexrelid
    JOIN pg_stat_all_indexes psai ON x.indexrelid = psai.indexrelid
) AS foo ON t.tablename = foo.ctablename AND t.schemaname = foo.schemaname
WHERE t.schemaname NOT IN ('pg_catalog', 'information_schema')
ORDER BY 1,2;

Duplicate indexes 

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SELECT pg_size_pretty(sum(pg_relation_size(idx))::bigint) as size,
       (array_agg(idx))[1] as idx1, (array_agg(idx))[2] as idx2,
       (array_agg(idx))[3] as idx3, (array_agg(idx))[4] as idx4
FROM (
    SELECT indexrelid::regclass as idx, (indrelid::text ||E'\n'|| indclass::text ||E'\n'|| indkey::text ||E'\n'||
                                         coalesce(indexprs::text,'')||E'\n' || coalesce(indpred::text,'')) as key
    FROM pg_index) sub
GROUP BY key HAVING count(*)>1
ORDER BY sum(pg_relation_size(idx)) DESC;

Maintenance

PostgreSQL wiki

CLUSTER-ing

CLUSTER

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CLUSTER [VERBOSE] table_name [ USING index_name ]
CLUSTER [VERBOSE]

CLUSTER instructs PostgreSQL to cluster the table specified by table_name based on the index specified by index_name. The index must already have been defined on table_name.

When a table is clustered, it is physically reordered based on the index information.

VACUUM-ing

Proper vacuuming, particularly autovacuum configuration, is crucial to a fast and reliable database.

Introduction to VACUUM, ANALYZE, EXPLAIN, and COUNT

It is not advised to run VACUUM FULL, instead look at clustering. VACUUM FULL is a much more intensive task and acquires an ACCESS EXCLUSIVE lock on the table, blocking reads and writes. Whilst CLUSTER also does acquire this lock it’s a less intensive and faster process.

Finding number of dead rows 

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SELECT relname, n_dead_tup FROM pg_stat_user_tables WHERE n_dead_tup <> 0 ORDER BY 2 DESC;

Finding last vacuum/auto-vacuum date 

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SELECT relname, last_vacuum, last_autovacuum FROM pg_stat_user_tables;

Checking auto-vacuum is enabled 

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SELECT name, setting FROM pg_settings WHERE name='autovacuum';

View all auto-vacuum setting 

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SELECT * from pg_settings where category like 'Autovacuum';

Locks

Looking at granted locks 

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SELECT relation::regclass, * FROM pg_locks WHERE NOT granted;

Сombination of blocked and blocking activity 

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SELECT blocked_locks.pid     AS blocked_pid,
         blocked_activity.usename  AS blocked_user,
         blocking_locks.pid     AS blocking_pid,
         blocking_activity.usename AS blocking_user,
         blocked_activity.query    AS blocked_statement,
         blocking_activity.query   AS current_statement_in_blocking_process
   FROM  pg_catalog.pg_locks         blocked_locks
    JOIN pg_catalog.pg_stat_activity blocked_activity  ON blocked_activity.pid = blocked_locks.pid
    JOIN pg_catalog.pg_locks         blocking_locks 
        ON blocking_locks.locktype = blocked_locks.locktype
        AND blocking_locks.database IS NOT DISTINCT FROM blocked_locks.database
        AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation
        AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page
        AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple
        AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid
        AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid
        AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid
        AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid
        AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
        AND blocking_locks.pid != blocked_locks.pid

    JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
   WHERE NOT blocked_locks.granted;