Re: [PERFORM] [HACKERS] temporary table vs array performance

[Pavel Stehule <pavel.stehule@xxxxxxxxx>]

2016-09-26 17:39 GMT+02:00 dbyzaa@xxxxxxx <dbyzaa@xxxxxxx>:

test:

create type  h3 as (id int,name char(10));

CREATE or replace FUNCTION proc17() 
RETURNS SETOF h3  AS $$ 
DECLARE
v_rec h3;
BEGIN 
    create temp table abc(id int,name varchar) on commit drop;
insert into abc select 1,'lw';
insert into abc select 2,'lw2';
for v_rec in
select * from abc loop
return next v_rec;
end loop;
END; 
$$ 
LANGUAGE plpgsql;


CREATE or replace FUNCTION proc16() 
RETURNS   SETOF h3 AS $$ 
DECLARE
 id_array int[];
 name_arr varchar[];
 v_rec h3;
BEGIN 
    id_array =array[1,2];
    name_arr=array['lw','lw2'];
for v_rec in
select unnest(id_array)  ,unnest(name_arr) loop
return next v_rec;                
end loop;
END; 
$$ 
LANGUAGE plpgsql;
postgres=# select * from proc17();
 id |    name    
----+------------
  1 | lw        
  2 | lw2       
(2 rows)

Time: 68.372 ms
postgres=# select * from proc16();
 id |    name    
----+------------
  1 | lw        
  2 | lw2       
(2 rows)

Time: 1.357 ms

temp talbe result:

[postgres@pg95 test_sql]$ pgbench -M prepared -n -r -c 2 -j 2 -T 10 -f temporary_test_1.sql 
transaction type: Custom query
scaling factor: 1
query mode: prepared
number of clients: 2
number of threads: 2
duration: 10 s
number of transactions actually processed: 5173
latency average: 3.866 ms
tps = 517.229191 (including connections establishing)
tps = 517.367956 (excluding connections establishing)
statement latencies in milliseconds:
3.863798 select * from proc17();

array result:

[postgres@pg95 test_sql]$ pgbench -M prepared -n -r -c 2 -j 2 -T 10 -f arrary_test_1.sql 
transaction type: Custom query
scaling factor: 1
query mode: prepared
number of clients: 2
number of threads: 2
duration: 10 s
number of transactions actually processed: 149381
latency average: 0.134 ms
tps = 14936.875176 (including connections establishing)
tps = 14940.234960 (excluding connections establishing)
statement latencies in milliseconds:
0.132983 select * from proc16();

Array is not convenient to use in function, whether there are other methods can be replaced temp table in function

Temporary tables are pretty expensive - from more reasons, and horrible when you use fresh table for two rows only. More if you recreate it every transaction.

More often pattern is create first and delete repeatedly. Better don't use temp tables when it is necessary. It is one reason why PostgreSQL supports a arrays. Partially - PostgreSQL arrays are analogy to T-SQL memory tables.

Regards

Pavel

 

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dbyzaa@xxxxxxx