目录
一、环境信息
|------|-------------------------------|
| 名称 | 值 |
| CPU | X86 |
| 操作系统 | CentOS Linux release 8.5.2111 |
| 内存 | 4G |
| 逻辑核数 | 5 |
| DM版本 | 9.1.0.26 |
二、背景描述
生产环境SQL SERVER 存过执行中，对存过进行重建，在存过中包含临时表时，正在执行的会话因临时表统计信息变化等原因触发局部重编译，导致报错提示：2812 找不到存储过程 XXX。在不包含临时表的情况下，存过立即编译完成，有许多系统需从SQL SERVER迁移至达梦，来看看达梦在存过不包含临时表时，是什么样的现象。
三、数据准备
sql
DROP TABLE IF EXISTS SUN;
DROP TABLE IF EXISTS TEMP_T;
CREATE TABLE SUN
(
session_id INT
);
INSERT INTO SUN SELECT LEVEL FROM DUAL CONNECT BY LEVEL <= 10000;
COMMIT;
CREATE TABLE TEMP_T
(
session_id INT
) ;
CREATE OR REPLACE PROCEDURE DM_SUN()
AS
v_sql VARCHAR(4000);
BEGIN
dbms_output.enable;
v_sql := 'INSERT INTO TEMP_T SELECT * FROM SUN';
execute immediate v_sql;
v_sql := 'update TEMP_T set session_id = session_id + 1 where session_id % 9 = 0';
execute immediate v_sql;
DBMS_LOCK.SLEEP(20);
v_sql := 'update TEMP_T set session_id = session_id + 2 where session_id % 7 = 0';
execute immediate v_sql;
COMMIT;
dbms_output.put_line('OK');
EXCEPTION
WHEN OTHERS THEN
ROLLBACK;
dbms_output.put_line('FAIL');
RAISE;
END;
/四、实验步骤
0、参数确认
bash
[root@localhost ~]# cat /opt/Dm9/Data/DAMENG/dm.ini |grep DDL_WAIT_TIME
DDL_WAIT_TIME = 10 #Maximum waiting time in seconds for DDLs
这里是10s，如果怕模拟不出现象，可以适当拉长。
1、开启多个会话
sql
SELECT
SESS_ID,
THRD_ID,
A.USER_NAME,
REPLACE(SUBSTR(CLNT_IP, 1, INSTR(CLNT_IP, ':', -1) -1), '::FFFF:', '') AS CLNT_IP,
A.CLNT_VER,
A.APPNAME,
DATEDIFF(SS, LAST_RECV_TIME, SYSDATE) AS SQL_USED_TIME,
DBMS_LOB.SUBSTR(SF_GET_SESSION_SQL(SESS_ID)) AS SQL_TXT,
PARSE_TIME,
HARD_PARSE_TIME,
LOGIC_READ_CNT,
PHY_READ_CNT,
RECYCLE_LOGIC_READ_CNT,
RECYCLE_PHY_READ_CNT,
IO_WAIT_TIME,
MAX_MEM_USED MAX_MEM_USED_KB,
EXEC_CPU,
EXEC_TIME
FROM
V$SESSIONS A
JOIN V$SQL_STAT B ON A.SESS_ID = B.SESSID -- AND A.SQL_ID = B.SQL_ID
WHERE
A.STATE = 'ACTIVE'
ORDER BY
SQL_USED_TIME DESC;
两个会话对应的线程号分别是12431、12432。
2、追踪锁信息
bash
[root@localhost ~]# strace -e trace=futex -tt -T -f -y -yy -p $(pidof dmserver) 2>&1 | grep -E '12431|12432'只看12431、12432线程的加锁信息，这里会卡顿住，是正常现象，因为还没有执行SQL。
3、会话一调用存过
sql
CALL DM_SUN();4、会话二重建存过
sql
CREATE OR REPLACE PROCEDURE DM_SUN()
AS
v_sql VARCHAR(4000);
BEGIN
dbms_output.enable;
v_sql := 'INSERT INTO TEMP_T SELECT * FROM SUN';
execute immediate v_sql;
v_sql := 'update TEMP_T set session_id = session_id + 1 where session_id % 9 = 0';
execute immediate v_sql;
DBMS_LOCK.SLEEP(20);
v_sql := 'update TEMP_T set session_id = session_id + 2 where session_id % 7 = 0';
execute immediate v_sql;
COMMIT;
dbms_output.put_line('OK');
EXCEPTION
WHEN OTHERS THEN
ROLLBACK;
dbms_output.put_line('FAIL');
RAISE;
END;
/5、会话三查看事务等待关系
sql
WITH
-- 1. 原始等待数据
trx AS (
SELECT
ID AS waiter,
WAIT_FOR_ID AS holder,
WAIT_TIME,
THRD_ID
FROM V$TRXWAIT
),
-- 2. 找出根事务（不等待别人，但正被他人等待）
root AS (
SELECT DISTINCT holder AS root_id
FROM trx
WHERE holder NOT IN (SELECT waiter FROM trx)
),
-- 3. 递归构建阻塞链
wait_chain (trx_id, parent_id, wait_time, thrd_id, lvl, path) AS (
-- 根节点：没有父事务，没有等待时间
SELECT
r.root_id,
NULL,
NULL,
NULL,
1,
TO_CHAR(r.root_id)
FROM root r
UNION ALL
-- 递归：从当前等待者向下找它的子等待者
SELECT
t.waiter,
wc.trx_id,
t.WAIT_TIME,
t.THRD_ID,
wc.lvl + 1,
wc.path || ' -> ' || t.waiter
FROM wait_chain wc
JOIN trx t ON t.holder = wc.trx_id
)
-- 4. 去重关联会话信息（只取每个事务的第一个会话）
, sessions_dedup AS (
SELECT
TRX_ID,
SESS_ID,
SQL_TEXT,
ROW_NUMBER() OVER (PARTITION BY TRX_ID ORDER BY SESS_ID) AS rn
FROM SYS."V$SESSIONS"
)
-- 5. 最终输出，以树形缩进展示
SELECT
wc.lvl,
LPAD(' ', (wc.lvl - 1) * 3) || 'Trx ' || wc.trx_id AS blocking_tree,
wc.trx_id,
wc.wait_time,
wc.thrd_id,
s.SESS_ID,
s.SQL_TEXT AS current_sql,
wc.path AS chain_path,
CASE WHEN wc.lvl = 1 THEN
'SP_CANCEL_SESSION_OPERATION(' || s.SESS_ID || '); ' || 'SP_CLOSE_SESSION(' || s.SESS_ID || ');'
ELSE
NULL
END as KILL_SESS_SQL
FROM wait_chain wc
LEFT JOIN sessions_dedup s
ON s.TRX_ID = wc.trx_id
AND s.rn = 1 -- 确保每个事务只关联一条会话
ORDER BY wc.path; -- 用路径排序，保证树结构顺序
重建等待调用。
6、会话四查看持有锁
sql
WITH
-- 1. 原始等待数据
trx AS (
SELECT
ID AS waiter,
WAIT_FOR_ID AS holder,
WAIT_TIME,
THRD_ID
FROM V$TRXWAIT
),
-- 2. 找出根事务（不等待别人，但正被他人等待）
root AS (
SELECT DISTINCT holder AS root_id
FROM trx
WHERE holder NOT IN (SELECT waiter FROM trx)
),
-- 3. 递归构建阻塞链
wait_chain (trx_id, parent_id, wait_time, thrd_id, lvl, path) AS (
-- 根节点：没有父事务，没有等待时间
SELECT
r.root_id,
NULL,
NULL,
NULL,
1,
TO_CHAR(r.root_id)
FROM root r
UNION ALL
-- 递归：从当前等待者向下找它的子等待者
SELECT
t.waiter,
wc.trx_id,
t.WAIT_TIME,
t.THRD_ID,
wc.lvl + 1,
wc.path || ' -> ' || t.waiter
FROM wait_chain wc
JOIN trx t ON t.holder = wc.trx_id
)
-- 4. 去重关联会话信息（只取每个事务的第一个会话）
, sessions_dedup AS (
SELECT
TRX_ID,
SESS_ID,
SQL_TEXT,
ROW_NUMBER() OVER (PARTITION BY TRX_ID ORDER BY SESS_ID) AS rn
FROM SYS."V$SESSIONS"
)
SELECT
O.OWNER,
O.OBJECT_NAME,
O.OBJECT_TYPE,
L.THRD_ID, -- 锁的创建者线程号
L.TRX_ID, -- 所属事务 ID
L.LTYPE, -- 锁类型：TID 锁、对象锁
L.LMODE, -- 锁模式：S 锁、X 锁、IX 锁、IS 锁
L.BLOCKED, -- 是否处于上锁等待状态。0 表示已上锁成功；1 表示处于上锁等待状态
L.TABLE_ID, -- 对于对象锁，表示表对象或字典对象的 ID；对于 TID 锁，表示封锁记录对应的表 ID。-1 表示事务启动封锁自身的 TID
L.ROW_IDX, -- TID 锁封锁记录行信息。-1 表示事务启动封锁自身的 TID
L.TID -- TID 锁对象事务 ID
FROM V$LOCK L
INNER JOIN
SYS.DBA_OBJECTS O
ON L.TABLE_ID = O.OBJECT_ID
WHERE L.TRX_ID IN (SELECT wc.trx_id FROM wait_chain wc);
线程12431拿到了存过的意向共享锁。
线程12432想拿到存过的排他锁，但没有获取到。
意向共享锁和排他锁互斥，所以等待是正常的。
7、追踪锁信息输出信息
bash
[root@localhost ~]# strace -e trace=futex -tt -T -f -y -yy -p $(pidof dmserver) 2>&1 | grep -E '12431|12432'
[pid 12431] 17:36:25.250615 futex(0x7f49847c0ddc, FUTEX_WAKE_PRIVATE, 2147483647) = 1 <0.000060>
[pid 12431] 17:36:25.250990 futex(0x7f498ad566b8, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=99998720} <unfinished ...>
[pid 12431] 17:36:25.254333 <... futex resumed>) = 0 <0.003272>
[pid 12431] 17:36:25.254498 futex(0x7f498ad56668, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000165>
[pid 12431] 17:36:28.963092 futex(0x7f497b1051dc, FUTEX_WAKE_PRIVATE, 1) = 1 <0.000152>
[pid 12431] 17:36:28.964599 futex(0x7f497b1051dc, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 12431] 17:36:28.964910 <... futex resumed>) = 1 <0.000270>
[pid 12432] 17:36:30.275137 futex(0x7f498b539a50, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=29999521}) = -1 ETIMEDOUT (连接超时) <0.030233>
[pid 12432] 17:36:30.305559 futex(0x7f498b539a00, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000018>
[pid 12432] 17:36:30.306915 futex(0x7f498b539a50, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=29994807}) = -1 ETIMEDOUT (连接超时) <0.030473>
[pid 12432] 17:36:30.337540 futex(0x7f498b539a00, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000018>
[pid 12432] 17:36:30.338908 futex(0x7f498b539a50, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=29998961}) = -1 ETIMEDOUT (连接超时) <0.030505>
[pid 12432] 17:36:30.369579 futex(0x7f498b539a00, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000021>
[pid 12432] 17:36:30.371506 futex(0x7f498b539a50, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=29998951}) = -1 ETIMEDOUT (连接超时) <0.030530>
[pid 12432] 17:36:30.402197 futex(0x7f498b539a00, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000020>
[pid 12432] 17:36:30.403516 futex(0x7f498b539a50, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=29998891}) = -1 ETIMEDOUT (连接超时) <0.030554>
[pid 12432] 17:36:30.434237 futex(0x7f498b539a00, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000019>
[pid 12432] 17:36:30.435571 futex(0x7f498b539a50, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=29998812}) = -1 ETIMEDOUT (连接超时) <0.030566>
[pid 12432] 17:36:30.466288 futex(0x7f498b539a00, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000018>
[pid 12432] 17:36:30.467634 futex(0x7f498b539a50, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=29999182}) = -1 ETIMEDOUT (连接超时) <0.030544>
[pid 12432] 17:36:30.498389 futex(0x7f498b539a00, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000022>futex：一种自旋锁+互斥锁组合的实现，在开始一段时间拿不到自旋锁，自动变为尝试拿互斥锁，减少CPU空转。
12431线程拿到锁。
12432线程差不多30ms内拿不到锁被唤醒，再次尝试加锁。