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Custom Alert - Total table bloat in database as a percentage

Description

This alert utilizes a very popular query used by PostgreSQL administrators to periodically monitor database table bloat.  How often you check database table bloat is dependent on your application, but every month or two is a reasonable time-frame.

Alert Definition

To create the alert, click on Alerts > Manage Alerts tab and create a Custom Alert of type Custom SQL Alert - Multiple Numeric Return. Configure the alert with values similar to these:

Alert Name: Long running 

Execution Interval: 30 minutes -- You may want to change the interval based on your database workload.  

Notification Text: Empty

Important: The SQL Text in DPA alerts are limited to 4000 characters.  The following SQL Statement was modified so it wouldn't exceed this limit.  Feel free to modify this alert and use other queries or variations based on your PostgreSQL versions and environment.   

SQL Statement:

WITH constants AS (SELECT current_setting('block_size')::numeric AS bs, 23 AS hdr, 8 AS ma),
no_stats AS (SELECT table_schema, table_name,n_live_tup::numeric as est_rows,pg_table_size(relid)::numeric as table_size
FROM information_schema.columns JOIN pg_stat_user_tables as psut ON table_schema = psut.schemaname AND table_name = psut.relname LEFT OUTER JOIN pg_stats ON table_schema = pg_stats.schemaname AND table_name = pg_stats.tablename AND column_name = attname
WHERE attname IS NULL AND table_schema NOT IN ('pg_catalog', 'information_schema')
GROUP BY table_schema, table_name, relid, n_live_tup),null_headers AS (SELECT hdr+1+(sum(case when null_frac <> 0 THEN 1 else 0 END)/8) as nullhdr,SUM((1-null_frac)*avg_width) as datawidth, MAX(null_frac) as maxfracsum, schemaname,tablename,hdr, ma, bs FROM pg_stats CROSS JOIN constants LEFT OUTER JOIN no_stats ON schemaname = no_stats.table_schema AND tablename = no_stats.table_name WHERE schemaname NOT IN ('pg_catalog', 'information_schema') AND no_stats.table_name IS NULL AND EXISTS ( SELECT 1 FROM information_schema.columns WHERE schemaname = columns.table_schema AND tablename = columns.table_name ) GROUP BY schemaname, tablename, hdr, ma, bs),
data_headers AS (SELECT ma, bs, hdr, 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 null_headers), table_estimates AS ( SELECT schemaname, tablename, bs, reltuples::numeric as est_rows, relpages * bs as table_bytes,
CEIL((reltuples*(datahdr + nullhdr2 + 4 + ma -(CASE WHEN datahdr%ma=0 THEN ma ELSE datahdr%ma END))/(bs-20))) * bs AS expected_bytes,reltoastrelid
FROM data_headers JOIN pg_class ON tablename = relname JOIN pg_namespace ON relnamespace = pg_namespace.oid AND schemaname = nspname
WHERE pg_class.relkind = 'r'),estimates_with_toast AS (SELECT schemaname, tablename, TRUE as can_estimate, est_rows,
table_bytes + ( coalesce(toast.relpages, 0) * bs ) as table_bytes, expected_bytes + ( ceil( coalesce(toast.reltuples, 0) / 4 ) * bs ) as expected_bytes
FROM table_estimates LEFT OUTER JOIN pg_class as toast ON table_estimates.reltoastrelid = toast.oid AND toast.relkind = 't'),
table_estimates_plus AS (SELECT current_database() as databasename,schemaname, tablename, can_estimate, est_rows,
CASE WHEN table_bytes > 0 THEN table_bytes::NUMERIC ELSE NULL::NUMERIC END AS table_bytes,
CASE WHEN expected_bytes > 0 THEN expected_bytes::NUMERIC ELSE NULL::NUMERIC END AS expected_bytes,
CASE WHEN expected_bytes > 0 AND table_bytes > 0 AND expected_bytes <= table_bytes THEN (table_bytes - expected_bytes)::NUMERIC ELSE 0::NUMERIC END AS bloat_bytes FROM estimates_with_toast
UNION ALL
SELECT current_database() as databasename, table_schema, table_name, FALSE, est_rows, table_size, NULL::NUMERIC, NULL::NUMERIC
FROM no_stats), bloat_data AS (select current_database() as databasename,schemaname, tablename, can_estimate,table_bytes, round(table_bytes/(1024^2)::NUMERIC,3) as table_mb, expected_bytes, round(expected_bytes/(1024^2)::NUMERIC,3) as expected_mb, round(bloat_bytes*100/table_bytes) as pct_bloat, round(bloat_bytes/(1024::NUMERIC^2),2) as mb_bloat, table_bytes, expected_bytes, est_rows FROM table_estimates_plus)
SELECT databasename ||'.'|| schemaname||'.'|| tablename || ' est rows: ' || est_rows, pct_bloat FROM bloat_data WHERE (pct_bloat >= 50 AND mb_bloat >= 20 ) OR ( pct_bloat >= 25 AND mb_bloat >= 1000 )
ORDER BY pct_bloat DESC

Units: %

High Threshold: Min 95, Max <blank> 

Medium Threshold: Min 50, Max 75

Low Threshold: Min 25, Max 50

Version history
Revision #:
4 of 4
Last update:
‎08-04-2020 09:05 AM
Updated by: