588
PostgreSQL 鎖等待診斷詳解
PostgreSQL和大多數傳統RDBMS一樣，都設計了大量的鎖來保證並發操作的數據一致性。
同時PG在設計鎖等待時，以隊列方式存儲等待鎖。
參考
ProcSleep()@src/backend/storage/lmgr/proc.c
https://blog.163.com/digoal@126/blog/static/163877040201352010122653/
因此，會出現一種問題。
例如一個長事務A持有一個表的某條記錄的更新鎖。
接下來的一個事務B要TRUNCATE這個表，會把這個鎖放到等待隊列去。
在接下來的事務C......如果請求的鎖和TRUNCATE表的鎖發生衝突，也會放到等待隊列去。
這其實是有利有弊的，利是什麼呢？
B在A釋放後，可以立即獲得鎖進行TRUNCATE。
弊是什麼？
排在B後麵的事務會被堵塞，雖然它們可能和A沒有鎖衝突，也需要等待。
弊端往往在某些湊巧的情況下起到放大效果。
例如一個表的操作非常頻繁，如果剛好有一個長事務在裏麵，然後又剛好有事務需要獲得一個排他鎖，那麼接下來的頻繁DML請求都會被堵塞。
一般可以用鎖超時來降低弊端帶來的這種影響，配置參數lock_timeout，如果鎖等待超過這個時間，會強行中斷，從等待隊列去除。
另外，如果我們沒有設置lock_timeout或者不方便設置lock_timeout的話，一旦發現數據庫出現了大量的等待，應該如何找到罪魁禍首呢？即處於等待狀態的查詢，它們到底在等待誰？
找到之後可以認為的殺掉這些罪魁禍首。
使用以下SQL
with t_wait as
(select a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.objid,a.objsubid,a.pid,a.virtualtransaction,a.virtualxid,a,transactionid,b.query,b.xact_start,b.query_start,b.usename,b.datname from pg_locks a,pg_stat_activity b where a.pid=b.pid and not a.granted),
t_run as
(select a.mode,a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.objid,a.objsubid,a.pid,a.virtualtransaction,a.virtualxid,a,transactionid,b.query,b.xact_start,b.query_start,b.usename,b.datname from pg_locks a,pg_stat_activity b where a.pid=b.pid and a.granted)
select r.locktype,r.mode,r.usename r_user,r.datname r_db,r.relation::regclass,r.pid r_pid,r.xact_start r_xact_start,r.query_start r_query_start,r.query r_query,
w.usename w_user,w.datname w_db,w.pid w_pid,w.xact_start w_xact_start,w.query_start w_query_start,w.query w_query
from t_wait w,t_run r where
r.locktype is not distinct from w.locktype and
r.database is not distinct from w.database and
r.relation is not distinct from w.relation and
r.page is not distinct from w.page and
r.tuple is not distinct from w.tuple and
r.classid is not distinct from w.classid and
r.objid is not distinct from w.objid and
r.objsubid is not distinct from w.objsubid
order by r.xact_start;
例如：
-[ RECORD 1 ]-+---------------------------------------------------------------------
locktype | relation
mode | ShareUpdateExclusiveLock
r_user | postgres
r_db | postgres
relation | tbl
r_pid | 24579
r_xact_start | 2015-05-10 09:43:53.956252+08
r_query_start | 2015-05-10 09:43:53.956252+08
r_query | autovacuum: VACUUM ANALYZE public.tbl (to prevent wraparound)
w_user | postgres
w_db | postgres
w_pid | 24737
w_xact_start | 2015-05-10 09:47:15.294562+08
w_query_start | 2015-05-10 09:47:15.294562+08
w_query | insert into tbl(crt_time) select now() from generate_series(1,1000);
.....
(1001 rows)
幹掉它：
postgres=# select pg_terminate_backend(24579);
-[ RECORD 1 ]--------+--
pg_terminate_backend | t
再次查詢，等待消失。
postgres=# with t_wait as
(select a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.objid,a.objsubid,a.pid,a.virtualtransaction,a.virtualxid,a,transactionid,b.query,b.xact_start,b.query_start,b.usename,b.datname from pg_locks a,pg_stat_activity b where a.pid=b.pid and not a.granted),
t_run as
(select a.mode,a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.objid,a.objsubid,a.pid,a.virtualtransaction,a.virtualxid,a,transactionid,b.query,b.xact_start,b.query_start,b.usename,b.datname from pg_locks a,pg_stat_activity b where a.pid=b.pid and a.granted)
select r.locktype,r.mode,r.usename r_user,r.datname r_db,r.relation::regclass,r.pid r_pid,r.xact_start r_xact_start,r.query_start r_query_start,r.query r_query,
w.usename w_user,w.datname w_db,w.pid w_pid,w.xact_start w_xact_start,w.query_start w_query_start,w.query w_query
from t_wait w,t_run r where
r.locktype is not distinct from w.locktype and
r.database is not distinct from w.database and
r.relation is not distinct from w.relation and
r.page is not distinct from w.page and
r.tuple is not distinct from w.tuple and
r.classid is not distinct from w.classid and
r.objid is not distinct from w.objid and
r.objsubid is not distinct from w.objsubid
order by r.xact_start;
(No rows)
實際上，這個查詢還不是完美，因為鎖等待實際上是一個TRUNCATE TABLE的操作造成的，而因為AUTO VACUUM FREEZE和TRUNCATE操作衝突了，所以這兩個會話的鎖都會對後麵的DML造成影響，實際上，我們要找到的應該是級別最高的鎖(TRUNCATE)，幹掉這個才是最重要的，普通的vacuum並不會和DML衝突。
所以我們需要改進一下這個查詢語句。
從pg_locks視圖的函數的源碼，可以知道mode是怎麼來的。
src/backend/utils/adt/lockfuncs.c
/*
* pg_lock_status - produce a view with one row per held or awaited lock mode
*/
Datum
pg_lock_status(PG_FUNCTION_ARGS)
{
......
Datum values[NUM_LOCK_STATUS_COLUMNS];
......
values[12] = CStringGetTextDatum(GetLockmodeName(instance->locktag.locktag_lockmethodid, mode));
......
}
src/backend/storage/lmgr/lock.c
/*
* Fetch the lock method table associated with a given lock
*/
LockMethod
GetLocksMethodTable(const LOCK *lock)
{
LOCKMETHODID lockmethodid = LOCK_LOCKMETHOD(*lock);
Assert(0 < lockmethodid && lockmethodid < lengthof(LockMethods));
return LockMethods[lockmethodid];
}
/* Names of lock modes, for debug printouts */
static const char *const lock_mode_names[] =
{
"INVALID",
"AccessShareLock",
"RowShareLock",
"RowExclusiveLock",
"ShareUpdateExclusiveLock",
"ShareLock",
"ShareRowExclusiveLock",
"ExclusiveLock",
"AccessExclusiveLock"
};
/*
* Data structures defining the semantics of the standard lock methods.
*
* The conflict table defines the semantics of the various lock modes.
*/
static const LOCKMASK LockConflicts[] = {
0,
/* AccessShareLock */
(1 << AccessExclusiveLock),
/* RowShareLock */
(1 << ExclusiveLock) | (1 << AccessExclusiveLock),
/* RowExclusiveLock */
(1 << ShareLock) | (1 << ShareRowExclusiveLock) |
(1 << ExclusiveLock) | (1 << AccessExclusiveLock),
/* ShareUpdateExclusiveLock */
(1 << ShareUpdateExclusiveLock) |
(1 << ShareLock) | (1 << ShareRowExclusiveLock) |
(1 << ExclusiveLock) | (1 << AccessExclusiveLock),
/* ShareLock */
(1 << RowExclusiveLock) | (1 << ShareUpdateExclusiveLock) |
(1 << ShareRowExclusiveLock) |
(1 << ExclusiveLock) | (1 << AccessExclusiveLock),
/* ShareRowExclusiveLock */
(1 << RowExclusiveLock) | (1 << ShareUpdateExclusiveLock) |
(1 << ShareLock) | (1 << ShareRowExclusiveLock) |
(1 << ExclusiveLock) | (1 << AccessExclusiveLock),
/* ExclusiveLock */
(1 << RowShareLock) |
(1 << RowExclusiveLock) | (1 << ShareUpdateExclusiveLock) |
(1 << ShareLock) | (1 << ShareRowExclusiveLock) |
(1 << ExclusiveLock) | (1 << AccessExclusiveLock),
/* AccessExclusiveLock */
(1 << AccessShareLock) | (1 << RowShareLock) |
(1 << RowExclusiveLock) | (1 << ShareUpdateExclusiveLock) |
(1 << ShareLock) | (1 << ShareRowExclusiveLock) |
(1 << ExclusiveLock) | (1 << AccessExclusiveLock)
};
static const LockMethodData default_lockmethod = {
AccessExclusiveLock, /* highest valid lock mode number */
LockConflicts,
lock_mode_names,
#ifdef LOCK_DEBUG
&Trace_locks
#else
&Dummy_trace
#endif
};
static const LockMethodData user_lockmethod = {
AccessExclusiveLock, /* highest valid lock mode number */
LockConflicts,
lock_mode_names,
#ifdef LOCK_DEBUG
&Trace_userlocks
#else
&Dummy_trace
#endif
};
src/include/storage/lock.h
/*
* These are the valid values of type LOCKMODE for all the standard lock
* methods (both DEFAULT and USER).
*/
/* NoLock is not a lock mode, but a flag value meaning "don't get a lock" */
#define NoLock 0
#define AccessShareLock 1 /* SELECT */
#define RowShareLock 2 /* SELECT FOR UPDATE/FOR SHARE */
#define RowExclusiveLock 3 /* INSERT, UPDATE, DELETE */
#define ShareUpdateExclusiveLock 4 /* VACUUM (non-FULL),ANALYZE, CREATE
* INDEX CONCURRENTLY */
#define ShareLock 5 /* CREATE INDEX (WITHOUT CONCURRENTLY) */
#define ShareRowExclusiveLock 6 /* like EXCLUSIVE MODE, but allows ROW
* SHARE */
#define ExclusiveLock 7 /* blocks ROW SHARE/SELECT...FOR
* UPDATE */
#define AccessExclusiveLock 8 /* ALTER TABLE, DROP TABLE, VACUUM
* FULL, and unqualified LOCK TABLE */
改進後的查詢如下：
用一個函數來將鎖轉換為數字，
postgres=# create or replace function f_lock_level(i_mode text) returns int as $$
declare
begin
case i_mode
when 'INVALID' then return 0;
when 'AccessShareLock' then return 1;
when 'RowShareLock' then return 2;
when 'RowExclusiveLock' then return 3;
when 'ShareUpdateExclusiveLock' then return 4;
when 'ShareLock' then return 5;
when 'ShareRowExclusiveLock' then return 6;
when 'ExclusiveLock' then return 7;
when 'AccessExclusiveLock' then return 8;
else return 0;
end case;
end;
$$ language plpgsql strict;
修改查詢語句，按鎖級別排序：
with t_wait as
(select a.mode,a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.objid,a.objsubid,
a.pid,a.virtualtransaction,a.virtualxid,a,transactionid,b.query,b.xact_start,b.query_start,
b.usename,b.datname from pg_locks a,pg_stat_activity b where a.pid=b.pid and not a.granted),
t_run as
(select a.mode,a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.objid,a.objsubid,
a.pid,a.virtualtransaction,a.virtualxid,a,transactionid,b.query,b.xact_start,b.query_start,
b.usename,b.datname from pg_locks a,pg_stat_activity b where a.pid=b.pid and a.granted)
select r.locktype,r.mode r_mode,r.usename r_user,r.datname r_db,r.relation::regclass,r.pid r_pid,
r.page r_page,r.tuple r_tuple,r.xact_start r_xact_start,r.query_start r_query_start,
now()-r.query_start r_locktime,r.query r_query,w.mode w_mode,w.pid w_pid,w.page w_page,
w.tuple w_tuple,w.xact_start w_xact_start,w.query_start w_query_start,
now()-w.query_start w_locktime,w.query w_query
from t_wait w,t_run r where
r.locktype is not distinct from w.locktype and
r.database is not distinct from w.database and
r.relation is not distinct from w.relation and
r.page is not distinct from w.page and
r.tuple is not distinct from w.tuple and
r.classid is not distinct from w.classid and
r.objid is not distinct from w.objid and
r.objsubid is not distinct from w.objsubid and
r.transactionid is not distinct from w.transactionid and
r.pid <> w.pid
order by f_lock_level(w.mode)+f_lock_level(r.mode) desc,r.xact_start;
現在可以排在前麵的就是鎖級別高的等待，優先幹掉這個。
-[ RECORD 1 ]-+---------------------------------------------------------------------
locktype | relation -- 衝突類型
r_mode | ShareUpdateExclusiveLock -- 持鎖模式
r_user | postgres -- 持鎖用戶
r_db | postgres -- 持鎖數據庫
relation | tbl -- 持鎖對象
r_pid | 25656 -- 持鎖進程
r_xact_start | 2015-05-10 14:11:16.08318+08 -- 持鎖事務開始時間
r_query_start | 2015-05-10 14:11:16.08318+08 -- 持鎖SQL開始時間
r_locktime | 00:01:49.460779 -- 持鎖時長
r_query | vacuum freeze tbl; -- 持鎖SQL,注意不一定是這個SQL帶來的鎖,也有可能是這個事務在之前執行的SQL加的鎖
w_mode | AccessExclusiveLock -- 等待鎖模式
w_pid | 26731 -- 等待鎖進程
w_xact_start | 2015-05-10 14:11:17.987362+08 -- 等待鎖事務開始時間
w_query_start | 2015-05-10 14:11:17.987362+08 -- 等待鎖SQL開始時間
w_locktime | 00:01:47.556597 -- 等待鎖時長
w_query | truncate tbl; -- 等待鎖SQL
-[ RECORD 2 ]-+---------------------------------------------------------------------
locktype | relation
r_mode | ShareUpdateExclusiveLock
r_user | postgres
r_db | postgres
relation | tbl
r_pid | 25656
r_xact_start | 2015-05-10 14:11:16.08318+08
r_query_start | 2015-05-10 14:11:16.08318+08
r_locktime | 00:01:49.460779
r_query | vacuum freeze tbl;
w_mode | RowExclusiveLock
w_pid | 25582
w_xact_start | 2015-05-10 14:11:22.845+08
w_query_start | 2015-05-10 14:11:22.845+08
w_locktime | 00:01:42.698959
w_query | insert into tbl(crt_time) select now() from generate_series(1,1000); -- 這個SQL其實等待的是truncate tbl的鎖;
......
鎖衝突判斷函數：
LockCheckConflicts()@src/backend/storage/lmgr/lock.c
我們可以創建一個函數用來殺掉對同一個對象某些鎖等待時間和等待進程超出閾值的進程。
例如擴展數據塊的鎖超出一定數量，我們想辦法殺掉，避免大量等待。
CREATE OR REPLACE FUNCTION public.f_kill_extend(i_interval interval, i_waiting bigint)
RETURNS void
LANGUAGE plpgsql
STRICT
AS $function$
declare
v_database oid;
v_relation oid;
v_pid int;
v_record record;
begin
if (pg_is_in_recovery()) then
return;
end if;
for v_record in with t_wait as
(select a.mode,a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.objid,a.objsubid,
a.pid,a.virtualtransaction,a.virtualxid,a,transactionid,b.query,b.xact_start,b.query_start,
b.usename,b.datname from pg_locks a,pg_stat_activity b where a.pid=b.pid and not a.granted),
t_run as
(select a.mode,a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.objid,a.objsubid,
a.pid,a.virtualtransaction,a.virtualxid,a,transactionid,b.query,b.xact_start,b.query_start,
b.usename,b.datname from pg_locks a,pg_stat_activity b where a.pid=b.pid and a.granted)
select r.locktype,r.mode r_mode,r.usename r_user,r.datname r_db,r.relation::regclass,r.pid r_pid,
r.page r_page,r.tuple r_tuple,r.xact_start r_xact_start,r.query_start r_query_start,
now()-r.query_start r_locktime,r.query r_query,w.mode w_mode,w.pid w_pid,w.page w_page,
w.tuple w_tuple,w.xact_start w_xact_start,w.query_start w_query_start,
now()-w.query_start w_locktime,w.query w_query
from t_wait w,t_run r where
r.locktype is not distinct from w.locktype and
r.database is not distinct from w.database and
r.relation is not distinct from w.relation and
r.page is not distinct from w.page and
r.tuple is not distinct from w.tuple and
r.classid is not distinct from w.classid and
r.objid is not distinct from w.objid and
r.objsubid is not distinct from w.objsubid and
r.transactionid is not distinct from w.transactionid and
r.pid <> w.pid
order by f_lock_level(w.mode)+f_lock_level(r.mode) desc,r.xact_start
LOOP
raise notice '%', v_record;
END LOOP;
for v_database,v_relation in select database,relation from pg_locks where
locktype='extend' and mode='ExclusiveLock' and not granted and
pid in (select pid from pg_stat_activity where now()-xact_start > i_interval)
group by 1,2 having count(*) > i_waiting
loop
perform pg_terminate_backend(pid) from pg_locks
where database=v_database and relation=v_relation;
end loop;
return;
end;
$function$;
例如：
psql -c "select f_kill_extend(interval '1 sec', 10);"
[參考]
1. https://blog.163.com/digoal@126/blog/static/163877040201352010122653/
2. src/backend/storage/lmgr/proc.c
/*
* ProcSleep -- put a process to sleep on the specified lock
*
* Caller must have set MyProc->heldLocks to reflect locks already held
* on the lockable object by this process (under all XIDs).
*
* The lock table's partition lock must be held at entry, and will be held
* at exit.
*
* Result: STATUS_OK if we acquired the lock, STATUS_ERROR if not (deadlock).
*
* ASSUME: that no one will fiddle with the queue until after
* we release the partition lock.
*
* NOTES: The process queue is now a priority queue for locking.
*
* P() on the semaphore should put us to sleep. The process
* semaphore is normally zero, so when we try to acquire it, we sleep.
*/
int
ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
{
LOCKMODE lockmode = locallock->tag.mode;
LOCK *lock = locallock->lock;
PROCLOCK *proclock = locallock->proclock;
uint32 hashcode = locallock->hashcode;
LWLockId partitionLock = LockHashPartitionLock(hashcode);
PROC_QUEUE *waitQueue = &(lock->waitProcs);
LOCKMASK myHeldLocks = MyProc->heldLocks;
bool early_deadlock = false;
bool allow_autovacuum_cancel = true;
int myWaitStatus;
PGPROC *proc;
int i;
/*
* Determine where to add myself in the wait queue.
*
* Normally I should go at the end of the queue. However, if I already
* hold locks that conflict with the request of any previous waiter, put
* myself in the queue just in front of the first such waiter. This is not
* a necessary step, since deadlock detection would move me to before that
* waiter anyway; but it's relatively cheap to detect such a conflict
* immediately, and avoid delaying till deadlock timeout.
*
* Special case: if I find I should go in front of some waiter, check to
* see if I conflict with already-held locks or the requests before that
* waiter. If not, then just grant myself the requested lock immediately.
* This is the same as the test for immediate grant in LockAcquire, except
* we are only considering the part of the wait queue before my insertion
* point.
*/
if (myHeldLocks != 0)
{
LOCKMASK aheadRequests = 0;
proc = (PGPROC *) waitQueue->links.next;
for (i = 0; i < waitQueue->size; i++)
{
/* Must he wait for me? */
if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks)
{
/* Must I wait for him ? */
if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks)
{
/*
* Yes, so we have a deadlock. Easiest way to clean up
* correctly is to call RemoveFromWaitQueue(), but we
* can't do that until we are *on* the wait queue. So, set
* a flag to check below, and break out of loop. Also,
* record deadlock info for later message.
*/
RememberSimpleDeadLock(MyProc, lockmode, lock, proc);
early_deadlock = true;
break;
}
/* I must go before this waiter. Check special case. */
if ((lockMethodTable->conflictTab[lockmode] & aheadRequests) == 0 &&
LockCheckConflicts(lockMethodTable,
lockmode,
lock,
proclock,
MyProc) == STATUS_OK)
{
/* Skip the wait and just grant myself the lock. */
GrantLock(lock, proclock, lockmode);
GrantAwaitedLock();
return STATUS_OK;
}
/* Break out of loop to put myself before him */
break;
}
/* Nope, so advance to next waiter */
aheadRequests |= LOCKBIT_ON(proc->waitLockMode);
proc = (PGPROC *) proc->links.next;
}
/*
* If we fall out of loop normally, proc points to waitQueue head, so
* we will insert at tail of queue as desired.
*/
}
else
{
/* I hold no locks, so I can't push in front of anyone. */
proc = (PGPROC *) &(waitQueue->links);
}
/*
* Insert self into queue, ahead of the given proc (or at tail of queue).
*/
SHMQueueInsertBefore(&(proc->links), &(MyProc->links));
waitQueue->size++;
lock->waitMask |= LOCKBIT_ON(lockmode);
/* Set up wait information in PGPROC object, too */
MyProc->waitLock = lock;
MyProc->waitProcLock = proclock;
MyProc->waitLockMode = lockmode;
MyProc->waitStatus = STATUS_WAITING;
/*
* If we detected deadlock, give up without waiting. This must agree with
* CheckDeadLock's recovery code, except that we shouldn't release the
* semaphore since we haven't tried to lock it yet.
*/
if (early_deadlock)
{
RemoveFromWaitQueue(MyProc, hashcode);
return STATUS_ERROR;
}
/* mark that we are waiting for a lock */
lockAwaited = locallock;
/*
* Release the lock table's partition lock.
*
* NOTE: this may also cause us to exit critical-section state, possibly
* allowing a cancel/die interrupt to be accepted. This is OK because we
* have recorded the fact that we are waiting for a lock, and so
* LockErrorCleanup will clean up if cancel/die happens.
*/
LWLockRelease(partitionLock);
/*
* Also, now that we will successfully clean up after an ereport, it's
* safe to check to see if there's a buffer pin deadlock against the
* Startup process. Of course, that's only necessary if we're doing Hot
* Standby and are not the Startup process ourselves.
*/
if (RecoveryInProgress() && !InRecovery)
CheckRecoveryConflictDeadlock();
/* Reset deadlock_state before enabling the timeout handler */
deadlock_state = DS_NOT_YET_CHECKED;
/*
* Set timer so we can wake up after awhile and check for a deadlock. If a
* deadlock is detected, the handler releases the process's semaphore and
* sets MyProc->waitStatus = STATUS_ERROR, allowing us to know that we
* must report failure rather than success.
*
* By delaying the check until we've waited for a bit, we can avoid
* running the rather expensive deadlock-check code in most cases.
*
* If LockTimeout is set, also enable the timeout for that. We can save a
* few cycles by enabling both timeout sources in one call.
*/
if (LockTimeout > 0)
{
EnableTimeoutParams timeouts[2];
timeouts[0].id = DEADLOCK_TIMEOUT;
timeouts[0].type = TMPARAM_AFTER;
timeouts[0].delay_ms = DeadlockTimeout;
timeouts[1].id = LOCK_TIMEOUT;
timeouts[1].type = TMPARAM_AFTER;
timeouts[1].delay_ms = LockTimeout;
enable_timeouts(timeouts, 2);
}
else
enable_timeout_after(DEADLOCK_TIMEOUT, DeadlockTimeout);
/*
* If someone wakes us between LWLockRelease and PGSemaphoreLock,
* PGSemaphoreLock will not block. The wakeup is "saved" by the semaphore
* implementation. While this is normally good, there are cases where a
* saved wakeup might be leftover from a previous operation (for example,
* we aborted ProcWaitForSignal just before someone did ProcSendSignal).
* So, loop to wait again if the waitStatus shows we haven't been granted
* nor denied the lock yet.
*
* We pass interruptOK = true, which eliminates a window in which
* cancel/die interrupts would be held off undesirably. This is a promise
* that we don't mind losing control to a cancel/die interrupt here. We
* don't, because we have no shared-state-change work to do after being
* granted the lock (the grantor did it all). We do have to worry about
* canceling the deadlock timeout and updating the locallock table, but if
* we lose control to an error, LockErrorCleanup will fix that up.
*/
do
{
PGSemaphoreLock(&MyProc->sem, true);
/*
* waitStatus could change from STATUS_WAITING to something else
* asynchronously. Read it just once per loop to prevent surprising
* behavior (such as missing log messages).
*/
myWaitStatus = MyProc->waitStatus;
/*
* If we are not deadlocked, but are waiting on an autovacuum-induced
* task, send a signal to interrupt it.
*/
if (deadlock_state == DS_BLOCKED_BY_AUTOVACUUM && allow_autovacuum_cancel)
{
PGPROC *autovac = GetBlockingAutoVacuumPgproc();
PGXACT *autovac_pgxact = &ProcGlobal->allPgXact[autovac->pgprocno];
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
/*
* Only do it if the worker is not working to protect against Xid
* wraparound.
*/
if ((autovac != NULL) &&
(autovac_pgxact->vacuumFlags & PROC_IS_AUTOVACUUM) &&
!(autovac_pgxact->vacuumFlags & PROC_VACUUM_FOR_WRAPAROUND))
{
int pid = autovac->pid;
StringInfoData locktagbuf;
StringInfoData logbuf; /* errdetail for server log */
initStringInfo(&locktagbuf);
initStringInfo(&logbuf);
DescribeLockTag(&locktagbuf, &lock->tag);
appendStringInfo(&logbuf,
_("Process %d waits for %s on %s."),
MyProcPid,
GetLockmodeName(lock->tag.locktag_lockmethodid,
lockmode),
locktagbuf.data);
/* release lock as quickly as possible */
LWLockRelease(ProcArrayLock);
ereport(LOG,
(errmsg("sending cancel to blocking autovacuum PID %d",
pid),
errdetail_log("%s", logbuf.data)));
pfree(logbuf.data);
pfree(locktagbuf.data);
/* send the autovacuum worker Back to Old Kent Road */
if (kill(pid, SIGINT) < 0)
{
/* Just a warning to allow multiple callers */
ereport(WARNING,
(errmsg("could not send signal to process %d: %m",
pid)));
}
}
else
LWLockRelease(ProcArrayLock);
/* prevent signal from being resent more than once */
allow_autovacuum_cancel = false;
}
/*
* If awoken after the deadlock check interrupt has run, and
* log_lock_waits is on, then report about the wait.
*/
if (log_lock_waits && deadlock_state != DS_NOT_YET_CHECKED)
{
StringInfoData buf;
const char *modename;
long secs;
int usecs;
long msecs;
initStringInfo(&buf);
DescribeLockTag(&buf, &locallock->tag.lock);
modename = GetLockmodeName(locallock->tag.lock.locktag_lockmethodid,
lockmode);
TimestampDifference(get_timeout_start_time(DEADLOCK_TIMEOUT),
GetCurrentTimestamp(),
&secs, &usecs);
msecs = secs * 1000 + usecs / 1000;
usecs = usecs % 1000;
if (deadlock_state == DS_SOFT_DEADLOCK)
ereport(LOG,
(errmsg("process %d avoided deadlock for %s on %s by rearranging queue order after %ld.%03d ms",
MyProcPid, modename, buf.data, msecs, usecs)));
else if (deadlock_state == DS_HARD_DEADLOCK)
{
/*
* This message is a bit redundant with the error that will be
* reported subsequently, but in some cases the error report
* might not make it to the log (eg, if it's caught by an
* exception handler), and we want to ensure all long-wait
* events get logged.
*/
ereport(LOG,
(errmsg("process %d detected deadlock while waiting for %s on %s after %ld.%03d ms",
MyProcPid, modename, buf.data, msecs, usecs)));
}
if (myWaitStatus == STATUS_WAITING)
ereport(LOG,
(errmsg("process %d still waiting for %s on %s after %ld.%03d ms",
MyProcPid, modename, buf.data, msecs, usecs)));
else if (myWaitStatus == STATUS_OK)
ereport(LOG,
(errmsg("process %d acquired %s on %s after %ld.%03d ms",
MyProcPid, modename, buf.data, msecs, usecs)));
else
{
Assert(myWaitStatus == STATUS_ERROR);
/*
* Currently, the deadlock checker always kicks its own
* process, which means that we'll only see STATUS_ERROR when
* deadlock_state == DS_HARD_DEADLOCK, and there's no need to
* print redundant messages. But for completeness and
* future-proofing, print a message if it looks like someone
* else kicked us off the lock.
*/
if (deadlock_state != DS_HARD_DEADLOCK)
ereport(LOG,
(errmsg("process %d failed to acquire %s on %s after %ld.%03d ms",
MyProcPid, modename, buf.data, msecs, usecs)));
}
/*
* At this point we might still need to wait for the lock. Reset
* state so we don't print the above messages again.
*/
deadlock_state = DS_NO_DEADLOCK;
pfree(buf.data);
}
} while (myWaitStatus == STATUS_WAITING);
/*
* Disable the timers, if they are still running. As in LockErrorCleanup,
* we must preserve the LOCK_TIMEOUT indicator flag: if a lock timeout has
* already caused QueryCancelPending to become set, we want the cancel to
* be reported as a lock timeout, not a user cancel.
*/
if (LockTimeout > 0)
{
DisableTimeoutParams timeouts[2];
timeouts[0].id = DEADLOCK_TIMEOUT;
timeouts[0].keep_indicator = false;
timeouts[1].id = LOCK_TIMEOUT;
timeouts[1].keep_indicator = true;
disable_timeouts(timeouts, 2);
}
else
disable_timeout(DEADLOCK_TIMEOUT, false);
/*
* Re-acquire the lock table's partition lock. We have to do this to hold
* off cancel/die interrupts before we can mess with lockAwaited (else we
* might have a missed or duplicated locallock update).
*/
LWLockAcquire(partitionLock, LW_EXCLUSIVE);
/*
* We no longer want LockErrorCleanup to do anything.
*/
lockAwaited = NULL;
/*
* If we got the lock, be sure to remember it in the locallock table.
*/
if (MyProc->waitStatus == STATUS_OK)
GrantAwaitedLock();
/*
* We don't have to do anything else, because the awaker did all the
* necessary update of the lock table and MyProc.
*/
return MyProc->waitStatus;
}
最後更新：2017-04-01 13:37:08
上一篇：
MongoDB權限管理代碼分析
下一篇： Greenplum TPC-H測試
- Intellij IDEA 快捷鍵整理（TonyCody）
- 物聯世界 矚目無錫
- VMware加強自身安全性，與IBM和Intel展開合作
- Java 25天基礎-DAY 05-麵向對象-構造函數
- ASP.NET入門隨想之抽象的力量
- 雲服務器 ECS 建站教程：ECS上搭建Docker(CentOS7)
- 最新Mac惡意軟件現身，安全專家提醒不要過於自信
- 深入淺出 spring-data-elasticsearch 之 ElasticSearch 架構初探（一）
- maven學習十之myEclipse搭建maven項目總結
- 利用DataGramPacket和DtaGramSocket編寫的從服務端獲取圖片