数据库内核月报

背景

目前PG的native partition分区性能还有优化空间，一种解决方法是使用pg_pathman插件，另一种方法是业务上直接插分区，还有一种方法是使用UDF函数接口（函数内部使用prepared statement来降低PARSE CPU开销）。

本文提供的是UDF的例子，以及性能比对。

例子

1、创建分区表

create table p (id int , info text, crt_time timestamp) partition by list (abs(mod(id,128)));    

2、创建128个分区

do language plpgsql $$  
declare  
begin  
  for i in 0..127 loop  
    execute format('create table p%s partition of p for values in (%s)', i, i);  
  end loop;  
end;  
$$;  

直接插分区主表

vi test.sql  
\set id random(1,2000000000)  
insert into p values (:id, 'test', now());  

性能

pgbench -M prepared -n -r -P 1 -f ./test.sql -c 64 -j 64 -T 120  
  
  
  
pgbench -M prepared -n -r -P 1 -f ./test.sql -c 32 -j 32 -T 120  
progress: 1.0 s, 26287.2 tps, lat 1.178 ms stddev 0.418  
progress: 2.0 s, 27441.8 tps, lat 1.166 ms stddev 0.393  
progress: 3.0 s, 27526.0 tps, lat 1.163 ms stddev 0.398  

批量插性能

vi test.sql  
  
insert into p values (1,'test',now()),(2,'test',now()),(3,'test',now()),(4,'test',now()),(5,'test',now()),(6,'test',now()),(7,'test',now()),(8,'test',now()),(9,'test',now()),(10,'test',now());  

pgbench -M prepared -n -r -P 1 -f ./test.sql -c 32 -j 32 -T 120  
progress: 1.0 s, 26240.5 tps, lat 1.179 ms stddev 0.462  
progress: 2.0 s, 28285.8 tps, lat 1.131 ms stddev 0.393  
progress: 3.0 s, 28185.1 tps, lat 1.135 ms stddev 0.423  
progress: 4.0 s, 28266.1 tps, lat 1.132 ms stddev 0.395  
progress: 5.0 s, 28248.9 tps, lat 1.133 ms stddev 0.438  
progress: 6.0 s, 26739.0 tps, lat 1.197 ms stddev 1.154  
progress: 7.0 s, 28075.1 tps, lat 1.140 ms stddev 0.426  
progress: 8.0 s, 28297.8 tps, lat 1.131 ms stddev 0.384  

使用UDF+绑定变量插分区

1、绑定变量的语法

postgres=# \h prepare  
Command:     PREPARE  
Description: prepare a statement for execution  
Syntax:  
PREPARE name [ ( data_type [, ...] ) ] AS statement  
  
postgres=# \h execute  
Command:     EXECUTE  
Description: execute a prepared statement  
Syntax:  
EXECUTE name [ ( parameter [, ...] ) ]  

2、写一个UDF，使用绑定变量插入

create or replace function ins_p(int, text, timestamp) returns void as $$  
declare  
  suffix text := abs(mod($1,128));  
begin  
  execute format('execute ps%s(%s, %L, %L)', suffix, $1, $2, $3);  
  exception when others then  
    execute format('prepare ps%s(int,text,timestamp) as insert into p%s (id,info,crt_time) values ($1,$2,$3)', suffix, suffix);  
    execute format('execute ps%s(%s, %L, %L)', suffix, $1, $2, $3);  
end;  
$$ language plpgsql strict;  

3、性能

vi test.sql  
  
\set id random(1,2000000000)  
select ins_p(:id, 'test', now()::timestamp);  

pgbench -M prepared -n -r -P 1 -f ./test.sql -c 32 -j 32 -T 120  
progress: 1.0 s, 192814.1 tps, lat 0.161 ms stddev 0.092  
progress: 2.0 s, 205480.6 tps, lat 0.156 ms stddev 0.061  
progress: 3.0 s, 209206.4 tps, lat 0.153 ms stddev 0.058  
progress: 4.0 s, 206333.8 tps, lat 0.155 ms stddev 0.061  

如果是BATCH写入，可以改一下这个UDF如下

create or replace function ins_p(int, text, timestamp) returns void as $$  
declare  
  suffix text := abs(mod($1,128));  
begin  
  execute format('execute ps%s(%s, %L, %L)', suffix, $1, $2, $3);  
  exception when others then  
    execute format('prepare ps%s(int,text,timestamp) as insert into p%s (id,info,crt_time) values ($1,$2,$3)', suffix, suffix);  
    execute format('execute ps%s(%s, %L, %L)', suffix, $1, $2, $3);  
end;  
$$ language plpgsql strict;  

create or replace function ins_p_batch(p[]) returns void as $$  
declare  
  i p;  
begin  
  foreach i in array $1 loop  
    perform ins_p(i.id, i.info, i.crt_time);  
  end loop;  
end;  
$$ language plpgsql strict;  

batch使用举例

postgres=# select count(*) from p;  
  count     
----------  
 28741670  
(1 row)  
  
Time: 390.775 ms  
postgres=# select ins_p_batch((select array_agg(p) from (select p from p limit 10000) t));  
 ins_p_batch   
-------------  
   
(1 row)  
  
Time: 247.861 ms  
postgres=# select count(*) from p;  
  count     
----------  
 28751670  
(1 row)  
  
Time: 383.485 ms  

postgres=# select array_agg(p) from (select p from p limit 10) t;  
-[ RECORD 1 ]-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  
array_agg | {"(1269675648,test,\"2019-01-09 17:08:35.432933\")","(1515917568,test,\"2019-01-09 17:08:35.435001\")","(137413760,test,\"2019-01-09 17:08:35.438484\")","(1750920192,test,\"2019-01-09 17:08:35.443544\")","(849316096,test,\"2019-01-09 17:08:35.448552\")","(891638016,test,\"2019-01-09 17:08:35.449074\")","(320902144,test,\"2019-01-09 17:08:35.449142\")","(95829120,test,\"2019-01-09 17:08:35.453658\")","(358048256,test,\"2019-01-09 17:08:35.454924\")","(1009512320,test,\"2019-01-09 17:08:35.457164\")"}  
  
Time: 1.771 ms  
  
postgres=# select ins_p_batch('{"(1269675648,test,\"2019-01-09 17:08:35.432933\")","(1515917568,test,\"2019-01-09 17:08:35.435001\")","(137413760,test,\"2019-01-09 17:08:35.438484\")","(1750920192,test,\"2019-01-09 17:08:35.443544\")","(849316096,test,\"2019-01-09 17:08:35.448552\")","(891638016,test,\"2019-01-09 17:08:35.449074\")","(320902144,test,\"2019-01-09 17:08:35.449142\")","(95829120,test,\"2019-01-09 17:08:35.453658\")","(358048256,test,\"2019-01-09 17:08:35.454924\")","(1009512320,test,\"2019-01-09 17:08:35.457164\")"}');  
 ins_p_batch   
-------------  
   
(1 row)  
  
Time: 0.841 ms  

性能

vi test.sql  
select ins_p_batch('{"(1269675648,test,\"2019-01-09\")","(1515917568,test,\"2019-01-09\")","(137413760,test,\"2019-01-09\")","(1750920192,test,\"2019-01-09\")","(849316096,test,\"2019-01-09\")","(891638016,test,\"2019-01-09\")","(320902144,test,\"2019-01-09\")","(95829120,test,\"2019-01-09\")","(358048256,test,\"2019-01-09\")","(1009512320,test,\"2019-01-09\")"}');  

一次插10行

pgbench -M prepared -n -r -P 1 -f ./test.sql -c 32 -j 32 -T 120  
progress: 1.0 s, 41637.4 tps, lat 0.745 ms stddev 0.742  
progress: 2.0 s, 42862.5 tps, lat 0.746 ms stddev 0.614  
progress: 3.0 s, 42417.1 tps, lat 0.754 ms stddev 0.689  
progress: 4.0 s, 42389.5 tps, lat 0.755 ms stddev 0.691  

应用程序直接写分区

性能

vi test.sql  
\set id random(1,2000000000)  
insert into p2 values (2,'test',now());  

pgbench -M prepared -n -r -P 1 -f ./test.sql -c 32 -j 32 -T 120  
progress: 1.0 s, 364350.5 tps, lat 0.085 ms stddev 0.208  
progress: 2.0 s, 379071.4 tps, lat 0.084 ms stddev 0.215  
progress: 3.0 s, 384452.1 tps, lat 0.083 ms stddev 0.188  