子事务可见性判断 & 性能
测试SQL
BEGIN;
PREPARE sel(integer) AS
SELECT count(*)
FROM contend
WHERE id BETWEEN $1 AND $1 + 100;
PREPARE upd(integer) AS
UPDATE contend SET val = val + 1
WHERE id IN ($1, $1 + 10, $1 + 20, $1 + 30);
SAVEPOINT a;
\set rnd random(1,990)
EXECUTE sel(10 * :rnd + :client_id + 1);
EXECUTE upd(10 * :rnd + :client_id);
SAVEPOINT a;
\set rnd random(1,990)
EXECUTE sel(10 * :rnd + :client_id + 1);
EXECUTE upd(10 * :rnd + :client_id);
...
SAVEPOINT a;
\set rnd random(1,990)
EXECUTE sel(10 * :rnd + :client_id + 1);
EXECUTE upd(10 * :rnd + :client_id);
DEALLOCATE ALL;
COMMIT;
子事务：tps = 167.382164
pgbench -f subtrans.sql -n -c 6 -T 600
transaction type: subtrans.sql
scaling factor: 1
query mode: simple
number of clients: 6
number of threads: 1
duration: 600 s
number of transactions actually processed: 100