同一函数之间的 PL/pgSQL 死锁

Question

我目前在 PostgreSQL 11.3 上运行 tpc-c benchmark，遇到了一个在 Oracle 上从未出现过的棘手死锁问题（类似 sql）。

问题函数是

create or replace
function bmsql_func_payment
(
    in_w_id integer,
    in_d_id integer,
    in_c_w_id integer,
    in_c_d_id integer,
    in_h_amount double precision,
    in_c_id integer,
    in_c_last varchar
) returns void as $$
declare
v_c_id integer := in_c_id;
v_d_name varchar(10);
v_w_name varchar(10);
v_c_data varchar(500);
v_c_credit char(2);
v_rowid tid;
BEGIN
-- @deadlock on bmsql_district
UPDATE bmsql_district SET d_ytd = d_ytd + in_h_amount
    WHERE d_w_id = in_w_id AND d_id = in_d_id
    RETURNING d_name INTO v_d_name;
-- @deadlock on bmsql_warehouse
UPDATE bmsql_warehouse SET w_ytd = w_ytd + in_h_amount
    WHERE w_id = in_w_id RETURNING w_name INTO v_w_name;

if in_c_last IS NOT NULL THEN
    v_rowid := bmsql_func_rowid_from_clast(in_w_id, in_d_id, in_c_last);
    SELECT c_credit, c_id INTO v_c_credit, v_c_id
        FROM bmsql_customer WHERE ctid = v_rowid;
ELSE
    SELECT c_credit INTO v_c_credit
        FROM bmsql_customer
        WHERE c_w_id = in_c_w_id AND c_d_id = in_c_d_id AND c_id = v_c_id;
END IF;

-- v_c_balance = v_c_balance - in_h_amount;
IF v_c_credit = 'GC' THEN
    UPDATE bmsql_customer
        SET c_balance = c_balance - in_h_amount,
        c_ytd_payment = c_ytd_payment + in_h_amount,
        c_payment_cnt = c_payment_cnt + 1
        WHERE c_w_id = in_c_w_id AND c_d_id = in_c_d_id AND c_id = v_c_id;
ELSE
    UPDATE bmsql_customer
        SET c_balance = c_balance - in_h_amount,
        c_ytd_payment = c_ytd_payment + in_h_amount,
        c_payment_cnt = c_payment_cnt + 1,
        c_data = v_c_data
        WHERE c_w_id = in_c_w_id AND c_d_id = in_c_d_id AND c_id = v_c_id
        RETURNING c_data INTO v_c_data;
    INSERT INTO bmsql_history
        (h_c_id, h_c_d_id, h_c_w_id, h_d_id, h_w_id, h_date, h_amount, h_data)
        VALUES
        (v_c_id, in_c_d_id, in_c_w_id, in_d_id, in_w_id,
        clock_timestamp(), in_h_amount, v_w_name || v_d_name);
END IF;
END;
$$ LANGUAGE plpgsql;

从日志中，似乎几个相同的函数之间发生了死锁，我不知道为什么这是可能的，因为它们都以相同的顺序持有锁？

死锁日志：

2019-07-26 14:19:03.418 CST,"bmsql","postgres",72147,"127.0.0.1:36051",5d3a9b56.119d3,3,"SELECT",2019-07-26 14:19:02 CST,21/4,356156,ERROR,40P01,"deadlock detected","Process 72147 waits for ShareLock on transaction 356150; blocked by process 72160.
Process 72160 waits for ShareLock on transaction 356137; blocked by process 72138.
Process 72138 waits for ShareLock on transaction 356153; blocked by process 72145.
Process 72145 waits for ShareLock on transaction 356156; blocked by process 72147.
Process 72147: SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)
Process 72160: SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)
Process 72138: SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)
Process 72145: SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)","See server log for query details.",,,"while updating tuple (21,77) in relation ""bmsql_warehouse""
SQL statement ""UPDATE bmsql_warehouse SET w_ytd = w_ytd + in_h_amount
WHERE w_id = in_w_id RETURNING w_name""
PL/pgSQL function bmsql_func_payment(integer,integer,integer,integer,double precision,integer,character varying) line 13 at SQL statement","SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)",,"DeadLockReport, deadlock.c:1140",""
2019-07-26 14:19:03.476 CST,"bmsql","postgres",72132,"127.0.0.1:36036",5d3a9b56.119c4,3,"SELECT",2019-07-26 14:19:02 CST,6/2,356130,ERROR,40P01,"deadlock detected","Process 72132 waits for ShareLock on transaction 356132; blocked by process 72157.
Process 72157 waits for ShareLock on transaction 356137; blocked by process 72138.
Process 72138 waits for ShareLock on transaction 356153; blocked by process 72145.
Process 72145 waits for ShareLock on transaction 356152; blocked by process 72133.
Process 72133 waits for ShareLock on transaction 356130; blocked by process 72132.
Process 72132: SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)
Process 72157: SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)
Process 72138: SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)
Process 72145: SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)
Process 72133: SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)","See server log for query details.",,,"while updating tuple (67,70) in relation ""bmsql_warehouse""
SQL statement ""UPDATE bmsql_warehouse SET w_ytd = w_ytd + in_h_amount
WHERE w_id = in_w_id RETURNING w_name""
PL/pgSQL function bmsql_func_payment(integer,integer,integer,integer,double precision,integer,character varying) line 13 at SQL statement","SELECT bmsql_func_payment($1,$2,$3,$4,$5,$6,$7)",,"DeadLockReport, deadlock.c:1140",""
...

Answer 1

您是否尝试过在函数开始时对导致死锁的表进行显式锁定？这样，在函数处理走得太远之前，就会尽早获得锁。您可以将锁定语句添加到函数中的第一个查询或作为独立语句：

LOCK TABLE bmsql_district IN SHARE ROW EXCLUSIVE MODE;
LOCK TABLE bmsql_warehouse IN SHARE ROW EXCLUSIVE MODE;

您可能需要调整锁定级别。几个链接：

https://www.postgresql.org/docs/11/explicit-locking.html
https://www.citusdata.com/blog/2018/02/15/when-postgresql-blocks/