May 17, 2026, 11:40 PM

2026-05-18 06:40:19 +00:00
commit 64944cf004
896 changed files with 310709 additions and 0 deletions
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+-- Analyze stats for a table testanalyze(schema is public)
+
+dbaclass=# analyze testanalyze;
+ANALYZE
+
+-- For analyzing selected columns for emptab table ( schema is dbatest)
+
+dbaclass=# analyze dbatest.emptab (datname,datdba);
+ANALYZE
+
+dbaclass=# select relname,reltuples from pg_class where relname in ('testanalyze','emptab');
+relname      | reltuples
+-------------+-----------
+testanalyze  | 4
+emptab       | 4
+(2 rows)
+
+dbaclass=# select schemaname,relname,analyze_count,last_analyze,last_autoanalyze from pg_stat_user_tables where relname in ('testanalyze','emptab');
+schemaname  | relname     | analyze_count | last_analyze                     | last_autoanalyze
+------------+-------------+---------------+----------------------------------+------------------
+public      | testanalyze | 1             | 2020-07-21 17:00:49.687053+05:30 |
+dbatest     | emptab      | 1             | 2020-07-21 17:10:01.111517+05:30 |
+(2 rows)
+
+---Analyze command with verbose command
+
+dbaclass=# analyze verbose dbatest.emptab (datname,datdba);
+
+INFO:  analyzing "dbatest.emptab"
+INFO:  "emptab": scanned 1 of 1 pages, containing 4 live rows and 0 dead rows; 4 rows in sample, 4 estimated total rows
+ANALYZE
+
+---Analyze tables in the current schema that the user has access to.
+
+ 
+
+dbaclass=# analyze ;
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+-- Finding statistics level of a column ( orders.orderdate)
+-- statistics level range is 1-10000 ( where 100 means 1 percent,10000 means 100 percent)
+
+edbstore=> SELECT attname as column_name , attstattarget as stats_level FROM pg_attribute WHERE attrelid = (SELECT oid FROM pg_class WHERE relname = 'orders') and attname='orderdate';
+
+column_name  | stats_level
+-------------+-------------
+orderdate    | 1000
+(1 row)
+
+-- To change statistics level of a column:
+
+edbstore=> alter table orders alter column orderdate set statistics 1000;
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+dbaclass=# SELECT a.query,p.phase, p.blocks_total,p.blocks_done,p.tuples_total, p.tuples_done FROM pg_stat_progress_create_index p JOIN pg_stat_activity a ON p.pid = a.pid;
+
+-[ RECORD 1 ]+-------------------------------
+query        | reindex index test_idx;
+phase        | building index: scanning table
+blocks_total | 61281
+blocks_done  | 15331
+tuples_total | 0
+tuples_done  | 0
+
+(or)
+
+dbaclass=# select pid,datname,command,phase,tuples_total,tuples_done,partitions_total,partitions_done from pg_stat_progress_create_index;
+
+-[ RECORD 1 ]-
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+select * from pg_stat_progress_vacuum;
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+REINDEX rebuilds an index using the data stored in the index's table, replacing the old copy of the index. There are several scenarios in which to use REINDEX:
+
+- Rebuild particular index:
+
+postgres=# REINDEX INDEX TEST_IDX2;
+REINDEX
+
+-- Rebuild all indexes on a table:
+
+postgres=# REINDEX TABLE TEST;
+REINDEX
+
+-- Rebuild all indexes of tables in a schema:
+postgres=# reindex schema public;
+REINDEX
+
+-- Rebuild all indexes in a database :
+
+postgres=# reindex database dbaclass;
+REINDEX
+
+-- Reindex with verbose option:
+
+postgres=# reindex (verbose) table test;
+INFO: index "test_idx" was reindexed
+DETAIL: CPU: user: 5.44 s, system: 2.72 s, elapsed: 11.96 s
+INFO: index "test_idx2" was reindexed
+DETAIL: CPU: user: 3.34 s, system: 1.01 s, elapsed: 5.49 s
+INFO: index "pg_toast_17395_index" was reindexed
+DETAIL: CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s
+REINDEX
+
+Rebuild index without causing lock on the table:( using concurrently option) 
+
+postgres=# REINDEX ( verbose) table concurrently test;
+INFO: index "public.test_idx" was reindexed
+INFO: index "public.test_idx2" was reindexed
+INFO: index "pg_toast.pg_toast_17395_index" was reindexed
+INFO: table "public.test" was reindexed
+DETAIL: CPU: user: 11.09 s, system: 6.23 s, elapsed: 24.63 s.
+REINDEX
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+VACUUM - >  REMOVES DEAD ROWS, AND MARK THEM FOR REUSE, BUT IT DOESN’T RETURN THE SPACE TO ORACLE,. IT DOESN'T NEED EXCLUSIVE LOCK ON THE TABLE.
+
+-------------------------------------------------------------------------
+
+vacuum a table:
+
+dbaclass=# vacuum dbatest.emptab;
+VACUUM
+
+both vacuum and analyze:
+
+dbaclass=# vacuum analyze dbatest.emptab;
+VACUUM
+
+with verbose:
+
+dbaclass# vacuum verbose analyze dbatest.emptab;
+
+Monitor vacuum process( if vacuum process runs for a long time)
+
+dbaclass#select * from pg_stat_progress_vacuum;
+
+Check vacuum related information for the table
+
+dbaclass=# select schemaname,relname,last_vacuum,vacuum_count from pg_stat_user_tables where relname='emptab';
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+VACUUM FULL - > JUST LIKE MOVE COMMAND IN ORACLE . IT TAKES MORE TIME, BUT IT RETURNS THE SPACE TO OS BECAUSE OF ITS COMPLEX ALGORITHM. IT also requires additional disk space , which can store the new copy of the table., until the activity is completed. Also it locks the table exclusively, which block all operations on the table .
+
+-- Command to run vacuum full command for table:
+
+dbaclass=# VACUUM FULL dbatest.emptab;
+VACUUM
+
+ 
+
+DEMO TO CHECK HOW IT RECLAIMS SPACE:
+
+-- Check existing space and delete some data:
+dbaclass=# select pg_size_pretty(pg_relation_size('dbatest.emptab'));
+pg_size_pretty
+----------------
+114 MB
+(1 row)
+
+dbaclass=# delete from dbatest.emptab where oid=13634;
+DELETE 131072
+
+-- We can observe size is still same:
+
+dbaclass=# select pg_size_pretty(pg_relation_size('dbatest.emptab'));
+pg_size_pretty
+----------------
+114 MB
+(1 row)
+
+-- Run vacuum full and observe the space usage:
+
+dbaclass=# VACUUM FULL dbatest.emptab;
+VACUUM
+
+dbaclass=# select pg_size_pretty(pg_relation_size('dbatest.emptab'));
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+Autovacuum methods automates the executions vacuum,freeze and analyze commands.
+
+-- Find whether autovacuum is enabled or not:
+
+dbaclass=# select name,setting,short_desc,boot_val,pending_restart from pg_settings where name in ('autovacuum','track_counts');
+name.         | setting | short_desc                                | boot_val | pending_restart
+--------------+---------+-------------------------------------------+----------+-----------------
+autovacuum    | on      | Starts the autovacuum subprocess.         | on        | f
+track_counts  | on      | Collects statistics on database activity. | on        | f
+(2 rows)
+
+-- Find other autovacuum related parameter settings
+dbaclass=# select name,setting,short_desc,min_val,max_val,enumvals,boot_val,pending_restart from pg_settings where category like 'Autovacuum';
+
+
+- Change autovacuum settings:( they need restart)
+
+dbaclass=# alter system set autovacuum_max_workers=10 ;
+ALTER SYSTEM
+
+Now restart :
+
+pg_ctl stop
+pg_ctl start