PostgreSQL

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Introduction

Database Maintenance and Monitoring script

Monitor Index status dan size for optimization

Over optimizing is a thing We always our database to be performant, so in order to do that we keep things in memory/cache (see earlier) and we index things so we don’t have to scan everything on disk. But there is a trade-off when it comes to indexing your database. Each index the system has to maintain will slow down your write throughput on the database. This is fine when you do need to speed up queries, as long as they’re being utilized. If you added an index years ago, but something within your application changed and you no longer need it best to remove it. Postgres makes it simply to query for unused indexes so you can easily give yourself back some performance by removing them:

/*
 * Over optimizing is a thing
	We always our database to be performant, so in order to do that we keep things in memory/cache (see earlier) and we index things so we don’t have to scan everything on disk. 
	But there is a trade-off when it comes to indexing your database. 
	Each index the system has to maintain will slow down your write throughput on the database. 
	This is fine when you do need to speed up queries, as long as they’re being utilized. 
	If you added an index years ago, but something within your application changed and you no longer need it best to remove it.
	Postgres makes it simply to query for unused indexes so you can easily give yourself back some performance by removing them:
 */
SELECT
  schemaname || '.' || relname AS table,
  indexrelname AS index,
  pg_size_pretty(pg_relation_size(i.indexrelid)) AS index_size,
  idx_scan as index_scans
FROM pg_stat_user_indexes ui
JOIN pg_index i ON ui.indexrelid = i.indexrelid
--WHERE NOT indisunique AND idx_scan < 50 AND pg_relation_size(relid) > 5 * 8192
--where relname = 'ret_gen_tsm_targetomzetline'
where relname in ('ret_gen_tsm_targetomzetgrow','ret_gen_tsm_targetomzetline','ret_tsmrekap_category','ret_gen_tsmtarget_category')
ORDER BY relname asc, pg_relation_size(i.indexrelid) / nullif(idx_scan, 0) DESC NULLS FIRST,
--idx_scan asc,
pg_relation_size(i.indexrelid) desc
;

--drop index ret_gen_tsm_targetomzetline_tag_status_idx;

Monitor Temporary Table

/*
 * We all aware of the temp tables and many times developers are creating temp table for their ad-hoc testing purpose.
 * But unfortunately sometimes, they forget to drop unused temp tables, and temp tables keep active in those idle connections.
 * It also requires unnecessary utilization of disk space.
 * 
 * DBAs are responsible for identifying unused temp tables and then inform to developers so that they can drop their unused temp tables.
 */

SELECT
	n.nspname as SchemaName
	,c.relname as RelationName
	,CASE c.relkind
	WHEN 'r' THEN 'table'
	WHEN 'v' THEN 'view'
	WHEN 'i' THEN 'index'
	WHEN 'S' THEN 'sequence'
	WHEN 's' THEN 'special'
	END as RelationType
	,pg_catalog.pg_get_userbyid(c.relowner) as RelationOwner               
	,pg_size_pretty(pg_relation_size(n.nspname ||'.'|| c.relname)) as RelationSize
FROM pg_catalog.pg_class c
LEFT JOIN pg_catalog.pg_namespace n               
                ON n.oid = c.relnamespace
WHERE  c.relkind IN ('r','s') 
AND  (n.nspname !~ '^pg_toast' and nspname like 'pg_temp%')
ORDER BY pg_relation_size(n.nspname ||'.'|| c.relname) DESC

Monitor Dead Tupple

/*
 * Under the covers Postgres is essentially a giant append only log. 
 * When you write data it appends to the log, when you update data it marks the old record as invalid and writes a new one, 
 * when you delete data it just marks it invalid. Later Postgres comes through and vacuums those dead records (also known as tuples).
 * All those unvacuumed dead tuples are what is known as bloat. Bloat can slow down other writes and create other issues. 
 * Paying attention to your bloat and when it is getting out of hand can be key for tuning vacuum on your database.
 */

WITH constants AS (
  SELECT current_setting('block_size')::numeric AS bs, 23 AS hdr, 4 AS ma
), bloat_info AS (
  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, constants
    GROUP BY 1,2,3,4,5
  ) AS foo
), table_bloat AS (
  SELECT
    schemaname, tablename, 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
  FROM bloat_info
  JOIN pg_class cc ON cc.relname = bloat_info.tablename
  JOIN pg_namespace nn ON cc.relnamespace = nn.oid AND nn.nspname = bloat_info.schemaname AND nn.nspname <> 'information_schema'
), index_bloat AS (
  SELECT
    schemaname, tablename, bs,
    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 bloat_info
  JOIN pg_class cc ON cc.relname = bloat_info.tablename
  JOIN pg_namespace nn ON cc.relnamespace = nn.oid AND nn.nspname = bloat_info.schemaname AND nn.nspname <> 'information_schema'
  JOIN pg_index i ON indrelid = cc.oid
  JOIN pg_class c2 ON c2.oid = i.indexrelid
)
SELECT
  type, schemaname, object_name, bloat, pg_size_pretty(raw_waste) as waste
FROM
(SELECT
  'table' as type,
  schemaname,
  tablename as object_name,
  ROUND(CASE WHEN otta=0 THEN 0.0 ELSE table_bloat.relpages/otta::numeric END,1) AS bloat,
  CASE WHEN relpages < otta THEN '0' ELSE (bs*(table_bloat.relpages-otta)::bigint)::bigint END AS raw_waste
FROM
  table_bloat
    UNION
SELECT
  'index' as type,
  schemaname,
  tablename || '::' || iname as object_name,
  ROUND(CASE WHEN iotta=0 OR ipages=0 THEN 0.0 ELSE ipages/iotta::numeric END,1) AS bloat,
  CASE WHEN ipages < iotta THEN '0' ELSE (bs*(ipages-iotta))::bigint END AS raw_waste
FROM
  index_bloat) bloat_summary
ORDER BY raw_waste DESC, bloat DESC

Monitor Cache Hit Ratio

/*
 * monitor your cache hit ratio
 * URL : https://www.citusdata.com/blog/2019/03/29/health-checks-for-your-postgres-database/
*/
SELECT 
  sum(heap_blks_read) as heap_read,
  sum(heap_blks_hit)  as heap_hit,
  sum(heap_blks_hit) / (sum(heap_blks_hit) + sum(heap_blks_read)) as ratio
FROM 
  pg_statio_user_tables;

Monitoring Database Query Performance

/*
 * monitoring your database query performance. 
 * It records a lot of valuable stats about which queries are run, how fast they return, how many times their run, etc. 
 * Checking in on this set of queries regularly can tell you where is best to add indexes 
 * or optimize your application so your query calls may not be so excessive.
 * URL : https://www.citusdata.com/blog/2019/03/29/health-checks-for-your-postgres-database/
 * 
 * Jalankan : create extension pg_stat_statements; jika belum pernah dilakukan
 */
SELECT query, 
       calls,
       ceil(total_time) as total_time, 
       ceil(total_time / calls) as time_per_call, 
       ceil(stddev_time) as stddev_time, 
       rows, 
       rows / calls as rows_per_call,
       ceil(100.0 * shared_blks_hit / nullif(shared_blks_hit + shared_blks_read, 0)) AS hit_percent
FROM pg_stat_statements
WHERE query not similar to '%pg_%'
--WHERE query similar to '%omzetline%'
--and calls > 500
--ORDER BY calls desc
--ORDER BY total_time desc
order by time_per_call desc
--ORDER BY rows_per
LIMIT 100;

Locks held by Open Transactions (pg_locks)

/*
 * Script to find information about the Locks held by Open Transactions (pg_locks)
 * 
 * PostgreSQL view pg_locks contains the main information about the all types of lock of Database Server.
 * It contains one row per active lockable object.
 * This script is very helpful to all PostgreSQL Database Administrators.
*/

SELECT 
	pl.pid AS ProcessID
	,psa.datname AS DatabaseName
	,psa.usename AS UserName
	,psa.application_name AS ApplicationName
	,ps.relname AS ObjectName
	,psa.query_start AS QueryStartTime
	,psa.state AS QueryState
	,psa.query AS SQLQuery
	,pl.locktype
	,pl.tuple AS TupleNumber
	,pl.mode AS LockMode
	,pl.granted -- True if lock is held, false if lock is awaited
FROM pg_locks AS pl 
LEFT JOIN pg_stat_activity AS psa
	ON pl.pid = psa.pid
LEFT JOIN pg_class AS ps
	ON pl.relation = ps.oid

Check Trigger Status

SELECT * FROM pg_trigger
WHERE tgisinternal=false and tgenabled = 'D'

--tgrelid 'public.c_order'::regclass and

-- enable trigger 
-- ALTER TABLE m_product ENABLE TRIGGER m_product_trg;

-- Disable trigger 
-- ALTER TABLE m_product DISABLE TRIGGER m_product_trg; 

Monitor LIVE and DEAD Tupples

SELECT 
	relname AS ObjectName
	,pg_stat_get_live_tuples(c.oid) AS LiveTuples
	,pg_stat_get_dead_tuples(c.oid) AS DeadTuples
FROM pg_class c
--where relname like 'c_%'
order by pg_stat_get_dead_tuples(c.oid) desc;
--order by pg_stat_get_live_tuples(c.oid) desc;

Monitor LIVE and DEAD Tupples with AUTO VACUUM

SELECT 
    schemaname
    ,relname
    ,n_live_tup
    ,n_dead_tup
    ,last_autovacuum
FROM pg_stat_all_tables
ORDER BY n_dead_tup
    /(n_live_tup
      * current_setting('autovacuum_vacuum_scale_factor')::float8
      + current_setting('autovacuum_vacuum_threshold')::float8)
     DESC

How to

Convert Integer or numeric to row number

select 
    	generate_series(1,tot_wo) as row
from oez_gen_simple_wo sw