The daily checklist of a PostgreSQL DBA
We often get this question, What are the most important things a PostgreSQL DBA should do to guarantee optimal performance and reliability, Do we have checklist for PostgreSQL DBAs to follow daily ? Since we are getting this question too often, Thought let’s note it as blog post and share with community of PostgreSQL ecosystem. The only objective this post is to share the information, Please don’t consider this as a run-book or recommendation from MinervaDB PostgreSQL support. We at MinervaDB are not accountable of any negative performance in you PostgreSQL performance with running these scripts in production database infrastructure of your business, The following is a simple daily checklist for PostgreSQL DBA:
Task 1: Check that all the PostgreSQL instances are up and operational:
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pgrep -u postgres -fa -- -D |
What if you have several instances of PostgreSQL are running:
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pgrep -fa -- -D |grep postgres |
Task 2: Monitoring PostgreSQL logsRecord PostgreSQL error logs: Open postgresql.conf configuration file, Under the ERROR REPORTING AND LOGGING section of the file, use following config parameters:
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log_destination = 'stderr' logging_collector = on log_directory = 'pg_log' log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log' log_truncate_on_rotation = off log_rotation_age = 1d log_min_duration_statement = 0 log_connections = on log_duration = on log_hostname = on log_timezone = 'UTC' |
Save the postgresql.conf file and restart the PostgreSQL server:
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sudo service postgresql restart |
Task 3: Confirm PostgreSQL backup completed successfully
Use backup logs (possible only with PostgreSQL logical backup) to audit backup quality:
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$ pg_dumpall > /backup-path/pg-backup-dump.sql > /var/log/postgres/pg-backup-dump.log |
Task 4: Monitoring PostgreSQL Database Size:
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select datname, pg_size_pretty(pg_database_size(datname)) from pg_database order by pg_database_size(datname); |
Task 5: Monitor all PostgreSQL queries running (please repeat this task every 90 minutes during business / peak hours):
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SELECT pid, age(clock_timestamp(), query_start), usename, query FROM pg_stat_activity WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%' ORDER BY query_start desc; |
Task 6: Inventory of indexes in PostgreSQL database:
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select t.relname as table_name, i.relname as index_name, string_agg(a.attname, ',') as column_name from pg_class t, pg_class i, pg_index ix, pg_attribute a where t.oid = ix.indrelid and i.oid = ix.indexrelid and a.attrelid = t.oid and a.attnum = ANY(ix.indkey) and t.relkind = 'r' and t.relname not like 'pg_%' group by t.relname, i.relname order by t.relname, i.relname; |
Task 7: Finding the largest databases in your PostgreSQL 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 |
Task 8: when you are suspecting some serious performance bottleneck in PostgreSQL ? Especially when you suspecting transactions blocking each other:
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WITH RECURSIVE l AS ( SELECT pid, locktype, mode, granted, ROW(locktype,database,relation,page,tuple,virtualxid,transactionid,classid,objid,objsubid) obj FROM pg_locks ), pairs AS ( SELECT w.pid waiter, l.pid locker, l.obj, l.mode FROM l w JOIN l ON l.obj IS NOT DISTINCT FROM w.obj AND l.locktype=w.locktype AND NOT l.pid=w.pid AND l.granted WHERE NOT w.granted ), tree AS ( SELECT l.locker pid, l.locker root, NULL::record obj, NULL AS mode, 0 lvl, locker::text path, array_agg(l.locker) OVER () all_pids FROM ( SELECT DISTINCT locker FROM pairs l WHERE NOT EXISTS (SELECT 1 FROM pairs WHERE waiter=l.locker) ) l UNION ALL SELECT w.waiter pid, tree.root, w.obj, w.mode, tree.lvl+1, tree.path||'.'||w.waiter, all_pids || array_agg(w.waiter) OVER () FROM tree JOIN pairs w ON tree.pid=w.locker AND NOT w.waiter = ANY ( all_pids ) ) SELECT (clock_timestamp() - a.xact_start)::interval(3) AS ts_age, replace(a.state, 'idle in transaction', 'idletx') state, (clock_timestamp() - state_change)::interval(3) AS change_age, a.datname,tree.pid,a.usename,a.client_addr,lvl, (SELECT count(*) FROM tree p WHERE p.path ~ ('^'||tree.path) AND NOT p.path=tree.path) blocked, repeat(' .', lvl)||' '||left(regexp_replace(query, 's+', ' ', 'g'),100) query FROM tree JOIN pg_stat_activity a USING (pid) ORDER BY path; |
Task 9: Identify bloated Tables in PostgreSQL :
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WITH constants AS ( -- define some constants for sizes of things -- for reference down the query and easy maintenance SELECT current_setting('block_size')::numeric AS bs, 23 AS hdr, 8 AS ma ), no_stats AS ( -- screen out table who have attributes -- which dont have stats, such as JSON 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 ( -- calculate null header sizes -- omitting tables which dont have complete stats -- and attributes which aren't visible 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 ( -- estimate header and row size 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 ( -- make estimates of how large the table should be -- based on row and page size 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 ( -- add in estimated TOAST table sizes -- estimate based on 4 toast tuples per page because we dont have -- anything better. also append the no_data tables 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 ( -- add some extra metadata to the table data -- and calculations to be reused -- including whether we cant estimate it -- or whether we think it might be compressed 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 ( -- do final math calculations and formatting 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 ) -- filter output for bloated tables SELECT databasename, schemaname, tablename, can_estimate, est_rows, pct_bloat, mb_bloat, table_mb FROM bloat_data -- this where clause defines which tables actually appear -- in the bloat chart -- example below filters for tables which are either 50% -- bloated and more than 20mb in size, or more than 25% -- bloated and more than 4GB in size WHERE ( pct_bloat >= 50 AND mb_bloat >= 10 ) OR ( pct_bloat >= 25 AND mb_bloat >= 1000 ) ORDER BY pct_bloat DESC; |
Task 10: Identify bloated indexes in PostgreSQL :
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-- btree index stats query -- estimates bloat for btree indexes WITH btree_index_atts AS ( SELECT nspname, indexclass.relname as index_name, indexclass.reltuples, indexclass.relpages, indrelid, indexrelid, indexclass.relam, tableclass.relname as tablename, regexp_split_to_table(indkey::text, ' ')::smallint AS attnum, indexrelid as index_oid FROM pg_index JOIN pg_class AS indexclass ON pg_index.indexrelid = indexclass.oid JOIN pg_class AS tableclass ON pg_index.indrelid = tableclass.oid JOIN pg_namespace ON pg_namespace.oid = indexclass.relnamespace JOIN pg_am ON indexclass.relam = pg_am.oid WHERE pg_am.amname = 'btree' and indexclass.relpages > 0 AND nspname NOT IN ('pg_catalog','information_schema') ), index_item_sizes AS ( SELECT ind_atts.nspname, ind_atts.index_name, ind_atts.reltuples, ind_atts.relpages, ind_atts.relam, indrelid AS table_oid, index_oid, current_setting('block_size')::numeric AS bs, 8 AS maxalign, 24 AS pagehdr, CASE WHEN max(coalesce(pg_stats.null_frac,0)) = 0 THEN 2 ELSE 6 END AS index_tuple_hdr, sum( (1-coalesce(pg_stats.null_frac, 0)) * coalesce(pg_stats.avg_width, 1024) ) AS nulldatawidth FROM pg_attribute JOIN btree_index_atts AS ind_atts ON pg_attribute.attrelid = ind_atts.indexrelid AND pg_attribute.attnum = ind_atts.attnum JOIN pg_stats ON pg_stats.schemaname = ind_atts.nspname -- stats for regular index columns AND ( (pg_stats.tablename = ind_atts.tablename AND pg_stats.attname = pg_catalog.pg_get_indexdef(pg_attribute.attrelid, pg_attribute.attnum, TRUE)) -- stats for functional indexes OR (pg_stats.tablename = ind_atts.index_name AND pg_stats.attname = pg_attribute.attname)) WHERE pg_attribute.attnum > 0 GROUP BY 1, 2, 3, 4, 5, 6, 7, 8, 9 ), index_aligned_est AS ( SELECT maxalign, bs, nspname, index_name, reltuples, relpages, relam, table_oid, index_oid, coalesce ( ceil ( reltuples * ( 6 + maxalign - CASE WHEN index_tuple_hdr%maxalign = 0 THEN maxalign ELSE index_tuple_hdr%maxalign END + nulldatawidth + maxalign - CASE /* Add padding to the data to align on MAXALIGN */ WHEN nulldatawidth::integer%maxalign = 0 THEN maxalign ELSE nulldatawidth::integer%maxalign END )::numeric / ( bs - pagehdr::NUMERIC ) +1 ) , 0 ) as expected FROM index_item_sizes ), raw_bloat AS ( SELECT current_database() as dbname, nspname, pg_class.relname AS table_name, index_name, bs*(index_aligned_est.relpages)::bigint AS totalbytes, expected, CASE WHEN index_aligned_est.relpages <= expected THEN 0 ELSE bs*(index_aligned_est.relpages-expected)::bigint END AS wastedbytes, CASE WHEN index_aligned_est.relpages <= expected THEN 0 ELSE bs*(index_aligned_est.relpages-expected)::bigint * 100 / (bs*(index_aligned_est.relpages)::bigint) END AS realbloat, pg_relation_size(index_aligned_est.table_oid) as table_bytes, stat.idx_scan as index_scans FROM index_aligned_est JOIN pg_class ON pg_class.oid=index_aligned_est.table_oid JOIN pg_stat_user_indexes AS stat ON index_aligned_est.index_oid = stat.indexrelid ), format_bloat AS ( SELECT dbname as database_name, nspname as schema_name, table_name, index_name, round(realbloat) as bloat_pct, round(wastedbytes/(1024^2)::NUMERIC) as bloat_mb, round(totalbytes/(1024^2)::NUMERIC,3) as index_mb, round(table_bytes/(1024^2)::NUMERIC,3) as table_mb, index_scans FROM raw_bloat ) -- final query outputting the bloated indexes -- change the where and order by to change -- what shows up as bloated SELECT * FROM format_bloat WHERE ( bloat_pct > 50 and bloat_mb > 10 ) ORDER BY bloat_mb DESC; |
Task 11: Monitor blocked and blocking activities in PostgreSQL:
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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; |
Task 12: Monitoring PostgreSQL Disk I/O performance:
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-- perform a "select pg_stat_reset();" when you want to reset counter statistics with all_tables as ( SELECT * FROM ( SELECT 'all'::text as table_name, sum( (coalesce(heap_blks_read,0) + coalesce(idx_blks_read,0) + coalesce(toast_blks_read,0) + coalesce(tidx_blks_read,0)) ) as from_disk, sum( (coalesce(heap_blks_hit,0) + coalesce(idx_blks_hit,0) + coalesce(toast_blks_hit,0) + coalesce(tidx_blks_hit,0)) ) as from_cache FROM pg_statio_all_tables --> change to pg_statio_USER_tables if you want to check only user tables (excluding postgres's own tables) ) a WHERE (from_disk + from_cache) > 0 -- discard tables without hits ), tables as ( SELECT * FROM ( SELECT relname as table_name, ( (coalesce(heap_blks_read,0) + coalesce(idx_blks_read,0) + coalesce(toast_blks_read,0) + coalesce(tidx_blks_read,0)) ) as from_disk, ( (coalesce(heap_blks_hit,0) + coalesce(idx_blks_hit,0) + coalesce(toast_blks_hit,0) + coalesce(tidx_blks_hit,0)) ) as from_cache FROM pg_statio_all_tables --> change to pg_statio_USER_tables if you want to check only user tables (excluding postgres's own tables) ) a WHERE (from_disk + from_cache) > 0 -- discard tables without hits ) SELECT table_name as "table name", from_disk as "disk hits", round((from_disk::numeric / (from_disk + from_cache)::numeric)*100.0,2) as "% disk hits", round((from_cache::numeric / (from_disk + from_cache)::numeric)*100.0,2) as "% cache hits", (from_disk + from_cache) as "total hits" FROM (SELECT * FROM all_tables UNION ALL SELECT * FROM tables) a ORDER BY (case when table_name = 'all' then 0 else 1 end), from_disk desc; |
References
- https://www.postgresql.org/developer/related-projects/
- https://www.postgresql.org/community/
- https://github.com/pgexperts
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