postgresql – Postgre性能不随着核心数量的增加而增加

CREATE TABLE school ( 
    id SERIAL NOT NULL PRIMARY KEY,name TEXT NOT NULL
);

CREATE TABLE class ( 
    id SERIAL NOT NULL PRIMARY KEY,name TEXT,school_id INTEGER NOT NULL REFERENCES school
);

CREATE TABLE student ( 
    id SERIAL NOT NULL PRIMARY KEY,class_id INTEGER NOT NULL REFERENCES class
);

-- ALL id and foreign keys have indexs

总共装载了1500万行,1500所学校,每所学校500班,每班200名学生.

之后创建一个简单的pgbench脚本

setrandom sId1 1 20000000
setrandom sId2 1 20000000
setrandom sId3 1 20000000

select count(*) from school s 
join class c on s.id=c.school_id 
join student stu on c.id=stu.class_id where s.id=:sId1;

select count(*) from school s 
join class c on s.id=c.school_id 
join student stu on c.id=stu.class_id where s.id=:sId2;

select count(*) from school s 
join class c on s.id=c.school_id 
join student stu on c.id=stu.class_id where s.id=:sId3;

现在运行脚本

pgbench -c 90 -f ./sql.sql  -n -t 1000

2个内核,7.5 GB,90个客户端 –

OUTPUT:
number of transactions actually processed: 90000/90000
tps = 1519.690555 (including connections establishing)
tps = 2320.408683 (excluding connections establishing

26个内核,30 GB,90个客户端 –

number of transactions actually processed: 90000/90000
tps = 1553.721286 (including connections establishing)
tps = 2405.664795 (excluding connections establishing)

题：
为什么我们从2核到26核才有80 tps？