Size of temp tables created in a particular session - postgresql

Question

I created a temp table using below query
Drop table if exists tmp_a;
Create temp table tmp_a
(
id int
);
Insert into tmp_a select generate_series(1,10000);
When I queried pg_stat_activity, it is showing as "IDLE" in current_query column for the above session.
I will get the size of all temp table from pg_class table using this query.
But I want the list of temp tables created for a particular session and the size of those temp tables i.e if I created two temp tables from two different sessions then the result should be like below
procpid | temp table name | size | username
12345 | tmp_a | 20 | gpadmin
12346 | tmp_b | 30 | gpadmin
Please share the query if anyone has it

Answer 1

It's actually simpler than you think --
The temporary schema namesapce is the same as the session id --
So...
SELECT
a.procpid as ProcessID,
a.sess_id as SessionID,
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
LEFT JOIN pg_catalog.pg_stat_activity a ON 'pg_temp_' || a.sess_id::varchar = n.nspname
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;
And you get --
processid | sessionid | schemaname | relationname | relationtype | relationowner | relationsize
-----------+-----------+------------+--------------+--------------+---------------+--------------
5006 | 9 | pg_temp_9 | tmp_a | table | gpadmin | 384 kB
5006 | 9 | pg_temp_9 | tmp_b | table | gpadmin | 384 kB
(2 rows)
Let's put that process to sleep -- and startup another....
gpadmin=#
[1]+ Stopped psql
[gpadmin#gpdb-sandbox ~]$ psql
psql (8.2.15)
Type "help" for help.
gpadmin=# SELECT nspname
FROM pg_namespace
WHERE oid = pg_my_temp_schema();
nspname
---------
(0 rows)
gpadmin=# Create temp table tmp_a( id int );
NOTICE: Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'id' as the Greenplum Database data distribution key for this table.
HINT: The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
CREATE TABLE
gpadmin=# SELECT nspname
FROM pg_namespace
WHERE oid = pg_my_temp_schema();
nspname
---------
pg_temp_10
(1 row)
... run the same query ...
processid | sessionid | schemaname | relationname | relationtype | relationowner | relationsize
-----------+-----------+------------+--------------+--------------+---------------+--------------
5006 | 9 | pg_temp_9 | tmp_a | table | gpadmin | 384 kB
5006 | 9 | pg_temp_9 | tmp_b | table | gpadmin | 384 kB
27365 | 10 | pg_temp_10 | tmp_a | table | gpadmin | 384 kB
(3 rows)