Show database bloat

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(summary of a few shortcomings of the query)
(Notes)
 
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== Notes ==
 
== Notes ==
  
This query is for informational purposes only. It provides a [http://archives.postgresql.org/pgsql-admin/2011-06/msg00015.php loose estimate] of table growth activity only, and should not be construed as a 100% accurate portrayal of space consumed by database objects. To obtain more accurate information about database bloat, please refer to the [http://www.postgresql.org/docs/9.1/static/pgstattuple.html pgstattuple] or [http://www.postgresql.org/docs/9.1/static/pgfreespacemap.html pg_freespacemap] contrib modules.
+
This query is for informational purposes only. It provides a [http://archives.postgresql.org/pgsql-admin/2011-06/msg00015.php loose estimate] of table growth activity only, and should not be construed as a 100% accurate portrayal of space consumed by database objects. To obtain more accurate information about database bloat, please refer to the [http://www.postgresql.org/docs/current/static/pgstattuple.html pgstattuple] or [http://www.postgresql.org/docs/current/static/pgfreespacemap.html pg_freespacemap] contrib modules.

Latest revision as of 17:03, 22 February 2013

Performance Snippets

Show database bloat

Works with PostgreSQL

>=8.0

Written in

SQL

Depends on

Nothing


This snippet displays the estimated amount of bloat in your tables and indices. Snippet is taken from Greg Sabino Mullane's excellent check_postgres script.

SELECT
  current_database(), schemaname, tablename, /*reltuples::bigint, relpages::bigint, otta,*/
  ROUND(CASE WHEN otta=0 THEN 0.0 ELSE sml.relpages/otta::numeric END,1) AS tbloat,
  CASE WHEN relpages < otta THEN 0 ELSE bs*(sml.relpages-otta)::bigint END AS wastedbytes,
  iname, /*ituples::bigint, ipages::bigint, iotta,*/
  ROUND(CASE WHEN iotta=0 OR ipages=0 THEN 0.0 ELSE ipages/iotta::numeric END,1) AS ibloat,
  CASE WHEN ipages < iotta THEN 0 ELSE bs*(ipages-iotta) END AS wastedibytes
FROM (
  SELECT
    schemaname, tablename, cc.reltuples, cc.relpages, bs,
    CEIL((cc.reltuples*((datahdr+ma-
      (CASE WHEN datahdr%ma=0 THEN ma ELSE datahdr%ma END))+nullhdr2+4))/(bs-20::float)) AS otta,
    COALESCE(c2.relname,'?') AS iname, COALESCE(c2.reltuples,0) AS ituples, COALESCE(c2.relpages,0) AS ipages,
    COALESCE(CEIL((c2.reltuples*(datahdr-12))/(bs-20::float)),0) AS iotta -- very rough approximation, assumes all cols
  FROM (
    SELECT
      ma,bs,schemaname,tablename,
      (datawidth+(hdr+ma-(case when hdr%ma=0 THEN ma ELSE hdr%ma END)))::numeric AS datahdr,
      (maxfracsum*(nullhdr+ma-(case when nullhdr%ma=0 THEN ma ELSE nullhdr%ma END))) AS nullhdr2
    FROM (
      SELECT
        schemaname, tablename, hdr, ma, bs,
        SUM((1-null_frac)*avg_width) AS datawidth,
        MAX(null_frac) AS maxfracsum,
        hdr+(
          SELECT 1+count(*)/8
          FROM pg_stats s2
          WHERE null_frac<>0 AND s2.schemaname = s.schemaname AND s2.tablename = s.tablename
        ) AS nullhdr
      FROM pg_stats s, (
        SELECT
          (SELECT current_setting('block_size')::numeric) AS bs,
          CASE WHEN substring(v,12,3) IN ('8.0','8.1','8.2') THEN 27 ELSE 23 END AS hdr,
          CASE WHEN v ~ 'mingw32' THEN 8 ELSE 4 END AS ma
        FROM (SELECT version() AS v) AS foo
      ) AS constants
      GROUP BY 1,2,3,4,5
    ) AS foo
  ) AS rs
  JOIN pg_class cc ON cc.relname = rs.tablename
  JOIN pg_namespace nn ON cc.relnamespace = nn.oid AND nn.nspname = rs.schemaname AND nn.nspname <> 'information_schema'
  LEFT JOIN pg_index i ON indrelid = cc.oid
  LEFT JOIN pg_class c2 ON c2.oid = i.indexrelid
) AS sml
ORDER BY wastedbytes DESC

[edit] Notes

This query is for informational purposes only. It provides a loose estimate of table growth activity only, and should not be construed as a 100% accurate portrayal of space consumed by database objects. To obtain more accurate information about database bloat, please refer to the pgstattuple or pg_freespacemap contrib modules.

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