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Important QueriesShankarnagEnterpriseDBINDEXAutovacuum - 3Vacuum-5System Queries-6CTID-40Func & Triggers-47

Autovacuum Demo on single tablecreate table :-create table test_auto(id integer primary key,name varchar(10));

Assign the autovacuum settings :-ALTER table test_auto SET (autovacuum_vacuum_threshold=50,autovacuum_analyze_threshold=50);

Inset rows in the table :-insert into test_auto values (generate_series(2,100000));

delete rows :-delete from test_auto where a% 2=0;

Now check the autovacuum is enabled on single table using below command or log files

select last_autovacuum,last_autoanalyze from pg_stat_all_tables where relname='test_auto';

\d+

disable auto vacuum :-ALTER TABLE sometable SET ( autovacuum_enabled = false, toast.autovacuum_enabled = false);

enable auto vacuum :-ALTER TABLE sometable SET ( autovacuum_enabled = true, toast.autovacuum_enabled = true);

Vacuum Demo :create table trunc( id int);

insert into trunc VALUES (generate_series(1,10));

select ctid,id from trunc ;

delete from trunc where id % 2=0;

select ctid,id from trunc ;

VACUUM verbose trunc ;

insert into trunc VALUES (2);

postgres=# select ctid,id from trunc ;System QueriesFind the number of live rows vs dead rows of a table :-

select relname as "Table", n_live_tup as "Live tuples", n_dead_tup as "Dead tuples"from pg_stat_user_tableswhere relname = 'my_table';

Finding the read activity statistics of tables in a databaseselect schemaname as "Schema Name" , relname as "Table Name", seq_tup_read+idx_tup_fetch as " no.of reads" from pg_stat_all_tablesorder by seq_tup_read+idx_tup_fetch;

Finding the write activity statistics of tables in a database::select schemaname as " Schema Name", relname as "Table Name, n_tup_ins+n_tup_upd+n_tup_del as "no.of writes" from pg_stat_all_tablesorder by n_tup_ins+n_tup_upd+n_tup_del;

Find out the I/O statistics of a tableselect relname as "Table", heap_blks_read as "Heap from disc", heap_blks_hit as "Heap from cache", idx_blks_read as "Index from disc", idx_blks_hit as "Index from cache", toast_blks_read as "Toast from disc", toast_blks_hit as "Toast from cache", tidx_blks_read as "Toast index disc", tidx_blks_hit as "Toast index cache"from pg_statio_user_tableswhere relname = 'my_table';

Find the size of all databases in a cluster::select datname as "Database name, pg_size_pretty(pg_database_size(datname)) as "Size of each database"from pg_database;

Find out the index statistics in a databaseselect relname as "Tablename", indexrelname as "Index name", idx_scan as "Index lookups", idx_tup_read as "Index entries", idx_tup_fetch as "Tuples fetched via index" from pg_stat_user_indexes order by relname,indexrelname;

Finding the lock statistics in a databaseselect pid as "Process id, mode, current_query as " Sql query" from pg_locks,pg_stat_activity where granted=false and locktype='transactionid' and pid=procpid order by pid,granted;

Finding the sizes of indexes in a databaseselect relname as "Table name", indexrelname as " Index name", pg_size_pretty( pg_relation_size( indexrelid ) ) as "Size"from pg_stat_all_indexeswhere schemaname = 'public' and relname='users'order by pg_relation_size( indexrelid ) desc;

Finding the Database statistics in a clusterSelect datname as "Database", numbackends as "Backends", xact_commit as "Xact Committed", xact_rollback as "Xact Rolled Back", blks_read as "Blocks Read", blks_hit as "Blocks Hit",(pg_database_size(datid) / 1024)::int as "Size (KB)"FROM pg_stat_database dbWHERE UPPER(db.datname) != 'TEMPLATE0' AND UPPER(db.datname) != 'TEMPLATE1'ORDER BY "Database";

Finding the number of users connected to each Database in a clusterSELECT COUNT(datid) as "Count", datconnlimit "Connection Limit per Database", d.datname as "Database Name" FROM pg_database d LEFT JOIN pg_stat_activity s ON (s.datid = d.oid) GROUP BY 2,3 ORDER BY d.datname;

Size of each table inside the Database on PostgreSQL 8.4 on-words::SELECT tablename as " Table Name", pg_size_pretty(pg_total_relation_size(CAST(tablename AS TEXT))) as Total size of table",pg_size_pretty((pg_total_relation_size(CAST(tablename AS TEXT)) - pg_relation_size(CAST(tablename ASTEXT)))) as "Index size FROM pg_tables WHERE schemaname != 'pg_catalog' AND schemaname != 'information_schema' ORDER BY pg_total_relation_size(CAST(tablename AS TEXT));List of tables in a Database:SELECT relname as "Table Name FROM pg_class WHERE relname !~ '^(pg_|sql_)' AND relkind = 'r';

List sequencesSELECT relname as " Sequence NameFROM pg_class WHERE relkind = 'S' AND relnamespace IN ( SELECT oid FROM pg_namespace WHERE nspname NOT LIKE 'pg_%' AND nspname != 'information_schema' );

List Triggers of a table:SELECT trg.tgname as "Trigger_name" FROM pg_trigger trg, pg_class tbl WHERE trg.tgrelid = tbl.oid AND tbl.relname = 'newtable';

Which tables are being updated the most and looking for vacuum ::select relname, /* pg_size_pretty( pg_relation_size( relid ) ) as table_size,pg_size_pretty( pg_total_relation_size( relid ) ) as table_total_size, */n_tup_upd, n_tup_hot_upd, n_live_tup, n_dead_tup, last_vacuum::date, last_autovacuum::date, last_analyze::date, last_autoanalyze::datefrom pg_stat_all_tableswhere relid in (select oid from pg_classwhere relnamespace not in(select oid from pg_namespacewhere nspname in ('information_schema', 'pg_catalog','pg_toast', 'edbhc' ) ) )order by n_tup_upd desc, schemaname, relname;

It gives index scanned less than 200 times and is not unique.SELECT idstat.relname AS table_name, indexrelname AS index_name, idstat.idx_scan AS times_used,pg_size_pretty(pg_relation_size(idstat.relname)) AS table_size,pg_size_pretty(pg_relation_size(indexrelname)) AS index_size, n_tup_upd + n_tup_ins + n_tup_del as num_writes, indexdef AS definitionFROM pg_stat_user_indexes AS idstat JOIN pg_indexes ON indexrelname = indexname JOIN pg_stat_user_tables AS tabstat ON idstat.relname = tabstat.relnameWHERE idstat.idx_scan < 200 AND indexdef !~* 'unique'ORDER BY idstat.relname, indexrelname;Size of each schema in a Database::SELECT nspname, sum(relpages * cast( 8192 AS bigint )) as "table size", sum( ( select sum(relpages) from pg_class i, pg_index idx where i.oid = idx.indexrelid and t.oid=idx.indrelid ) ) * cast( 8192 AS bigint ) as "index size", sum ( relpages * cast( 8192 AS bigint ) + ( select sum(relpages) from pg_class i, pg_index idx where i.oid = idx.indexrelid and t.oid=idx.indrelid ) * cast( 8192 AS bigint ) ) as "size" FROM pg_class t, pg_namespace WHERE relnamespace = pg_namespace.oid and pg_namespace.nspname not like 'pg_%' and pg_namespace.nspname != 'information_schema' and relkind = 'r' group by nspname;

Find out how many pages and tuples are used by a tableselect relname as "table", reltuples as "number of tuples", relpages as "number of 8kb pages" from pg_class where relname = 'table';

Find out the Primary key tables in a databaseSELECT tablename FROM pg_tables WHERE tablename IN (SELECT r.relname FROM pg_class r, pg_constraint c WHERE r.oid = c.conrelid AND c.contype = 'p') AND schemaname = 'public';

Which user PID is locking on which transaction processselect bl.pid as blocked_pid, a.usename as blocked_user,kl.pid as blocking_pid, ka.usename as blocking_user, a.current_query as blocked_statement from pg_catalog.pg_locks bl join pg_catalog.pg_stat_activity a on bl.pid = a.procpid join pg_catalog.pg_locks kl join pg_catalog.pg_stat_activity ka on kl.pid = ka.procpid on bl.transactionid = kl.transactionid and bl.pid != kl.pid where not bl.granted;

Checking the user permissionsSELECT relname as "Relation", relacl as "Access permissions" FROM pg_classWHERE relkind IN ('r', 'v', 'S') AND relname !~ '^pg_' ORDER BY relname;

Retrieving the name of the user associated with the current postgres backend.postgres=# select getpgusername(); getpgusername --------------- postgres

Retrieving the client encoding of the serverpostgres=# select pg_client_encoding(); pg_client_encoding -------------------- UTF8

SIGHUP signal to the postmaster, causing the configuration files to be reloaded by all server processes.

postgres=# Select pg_reload_conf();pg_reload_conf ---------------- t(1 row)

pg_rotate_logfile:: pg_rotate_logfile signals the log-file manager to switch to a new output file immediately and it works only when logtype is stderr.

postgres=# select pg_ls_dir('pg_log'); pg_ls_dir ------------------------------------------postgresql-2010-10-22_221941.log postgresql-2010-10-23_000000.log postgresql-2010-10-23_011320.log postgresql-2010-10-24_000000.logpostgres=# select pg_rotate_logfile(); pg_rotate_logfile ------------------- t(1 row)postgres=# select pg_ls_dir('pg_log'); pg_ls_dir ------------------------------------------postgresql-2010-10-22_221941.log postgresql-2010-10-23_000000.log postgresql-2010-10-23_011320.log postgresql-2010-10-24_000000.log postgresql-2010-10-24_135627.log5. pg_ls_dir -- It shows content of given directory except the special entries . and ...(it is treated as relative to $PGDATA). it is not possible (or i dont know how to) to go to another directories than $PGDATA.

postgres=# select pg_ls_dir('pg_xlog'); pg_ls_dir -------------------------- 000000010000000000000003 000000010000000000000004 000000010000000000000005 archive_status(4 rows)6. pg_sleep It makes the current sessions process sleep until seconds seconds have elapsed.Ex:postgres=# SELECT CURRENT_TIMESTAMP; SELECT pg_sleep(60); SELECT CURRENT_TIMESTAMP; now ---------------------------------- 2010-10-24 13:51:54.158547+05:30(1 row) pg_sleep ---------- (1 row) now ---------------------------------- 2010-10-24 13:52:54.186517+05:30(1 row)

pg_char_to_encoding convert from one from of encoding to anotherEX:- How do I convert a database in the ASCII format into one of the UTF-8 format?template1=# create database test with encoding='SQL_ASCII';CREATE DATABASEtemplate1=# \connect testYou are now connected to database "test".test=# create table a (x text);CREATE TABLEtest=# insert into a values ('');INSERT 33304378 1test=# select * from a;x--(1 row)Contd :-test=# update pg_database set encoding =pg_catalog.pg_char_to_encoding('UTF8') where datname='test';UPDATE 1test=# select * from a;x--(1 row)test=# \connect template1You are now connected to database "template1".template1=# \connect testYou are now connected to database "test".test=# select * from a;x--(1 row)

pg_postmaster_start_time Retrieves the postmaster start timepostgres=# select pg_postmaster_start_time(); pg_postmaster_start_time ------------------------------- 2010-09-01 11:39:36.472834-04(1 row)

pg_switch_xlog Generates manual switch on the current transaction log in the database.postgres=# select pg_xlogfile_name(pg_current_xlog_location()); pg_xlogfile_name -------------------------- 000000010000000000000009(1 row)postgres=# select pg_switch_xlog(); pg_switch_xlog ---------------- 0/A000000(1 row)postgres=# select pg_xlogfile_name(pg_current_xlog_insert_location()); pg_xlogfile_name -------------------------- 00000001000000000000000A(1 row)

pg_current_xlog_location -- displays the current transaction log write locationpostgres=# select pg_current_xlog_location(); pg_current_xlog_location -------------------------- 0/8000064(1 row)

pg_xlogfile_name extract the transaction log file name.postgres=# select pg_xlogfile_name('0/8000064'); pg_xlogfile_name -------------------------- 000000010000000000000008(1 row)

pg_current_xlog_insert_location Retrieves the current transaction log insertion file name.

postgres=# select pg_current_xlog_insert_location(); pg_current_xlog_insert_location --------------------------------- 0/A000064

pg_stat_get_numscans -- It shows the number of sequential scans occured on a table syntax: select pg_stat_get_numscans(oid);postgres=# select relfilenode,relname from pg_class where relname='test'; relfilenode | relname -------------+--------- 18328 | test(1 row)postgres=# select pg_stat_get_numscans(18328); pg_stat_get_numscans ---------------------- 4 (or)postgres=# select relname,seq_scan from pg_Stat_user_tables; relname | seq_scan --------------------+---------- sl_table | 0 sl_setsync | 0 test | 4

pg_stat_get_live_tuples -- Retrieves the number of live rows in a tablesyntax: select pg_stat_get_live_tuples(oid);postgres=# select relfilenode,relname from pg_class where relname='test'; relfilenode | relname -------------+--------- 18328 | test(1 row)postgres=# select pg_stat_get_live_tuples(18328); pg_stat_get_live_tuples ------------------------- 10(1 row)

pg_stat_get_dead_tuples -- Retrieves the dead rows in a table.Syntax: select pg_stat_get_dead_tuples(oid);postgres=# select pg_stat_get_dead_tuples(18328); pg_stat_get_dead_tuples ------------------------- 0(1 row)

CTID Demopostgres=# select pg_relation_size('emails'); pg_relation_size------------------ 8192

postgres=# select ctid,* from emails;

ctid | email--------+-------------------------------- (0,1) | 1995liufang@sima.com (0,2) | molly.nguyen@tenethealth.com (0,3) | edwyn0407@blackberry.net (0,4) | kathryn.canete@tenethealth.com (0,5) | akanwo@yahoo.com (0,6) | dnh@a.com (0,7) | cteng1230@gmail.com (0,8) | ajuvenillehood@aol.com (0,9) | derkmau@gmail.com (0,10) | gbarnes@remax.net(10 rows)postgres=# select * from emails where ctid='(0,8)'; email------------------------ ajuvenillehood@aol.com(1 row)

postgres=# delete from email where ctid < 5;ERROR: relation "email" does not existpostgres=# delete from emails where ctid < 5;ERROR: operator does not exist: tid < integerLINE 1: delete from emails where ctid < 5; ^HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.postgres=# delete from emails where email='ajuvenillehood@aol.com';DELETE 1postgres=# select ctid,* from emails; ctid | email--------+-------------------------------- (0,1) | 1995liufang@sima.com (0,2) | molly.nguyen@tenethealth.com (0,3) | edwyn0407@blackberry.net (0,4) | kathryn.canete@tenethealth.com (0,5) | akanwo@yahoo.com (0,6) | dnh@a.com (0,7) | cteng1230@gmail.com (0,9) | derkmau@gmail.com (0,10) | gbarnes@remax.net(9 rows)

postgres=# select * from emails where ctid='(0,8)'; email-------(0 rows)postgres=# \d clusterDid not find any relation named "cluster".postgres=# \h clusterCommand: CLUSTERDescription: cluster a table according to an indexSyntax:CLUSTER tablename [ USING indexname ]CLUSTER

postgres=# cluster emails;ERROR: there is no previously clustered index for table "emails"postgres=# VACUUM ANALYZE emails;VACUUMpostgres=# select * from emails where ctid='(0,8)'; email-------(0 rows)

postgres=# select ctid,* from emails; ctid | email--------+-------------------------------- (0,1) | 1995liufang@sima.com (0,2) | molly.nguyen@tenethealth.com (0,3) | edwyn0407@blackberry.net (0,4) | kathryn.canete@tenethealth.com (0,5) | akanwo@yahoo.com (0,6) | dnh@a.com (0,7) | cteng1230@gmail.com (0,9) | derkmau@gmail.com (0,10) | gbarnes@remax.net(9 rows)postgres=# select ctid,xmin,xmax,* from emails; ctid | xmin | xmax | email--------+------+------+-------------------------------- (0,1) | 575 | 0 | 1995liufang@sima.com (0,2) | 575 | 0 | molly.nguyen@tenethealth.com (0,3) | 575 | 0 | edwyn0407@blackberry.net (0,4) | 575 | 0 | kathryn.canete@tenethealth.com (0,5) | 575 | 0 | akanwo@yahoo.com (0,6) | 575 | 0 | dnh@a.com (0,7) | 575 | 0 | cteng1230@gmail.com (0,9) | 575 | 0 | derkmau@gmail.com (0,10) | 575 | 0 | gbarnes@remax.net(9 rows)

FUNCTIONScreate or replace function sum_val(i numeric, z numeric) returns numeric as$$beginreturn i+z;end;$$ language plpgsql;

create or replace function differ(x numeric, y numeric) returns void as$$declared numeric;begind:=x-y;raise notice 'Difference is: %',d;return;end;$$ language plpgsql;

select differ(10,5);create or replace function dis_cus(c_id numeric) returns void as$$declarerec RECORD;beginselect into rec * from customer where custid=c_id;if found thenraise notice 'Customer Name: %', rec.custname;raise notice 'Account No: %', rec.accountid;elseraise notice 'No Data';end if;return;end;$$ language plpgsql;

select differ(10,5);create or replace function dis() returns void as$$declarerec numeric;beginrec:=0;while rec