/* Finally wait for each such transaction to complete */
foreach(lc, holders)
{
VirtualTransactionId *lockholders = lfirst(lc);
while (VirtualTransactionIdIsValid(*lockholders))
{
VirtualXactLock(*lockholders, true);
lockholders++;
}
}
/*
* VirtualXactLockTableInsert
*
* Insert a lock showing that the given virtual transaction ID is running ---
* this is done at main transaction start when its VXID is assigned.
* The lock can then be used to wait for the transaction to finish.
*/
void
VirtualXactLockTableInsert(VirtualTransactionId vxid)
{
LOCKTAG tag;
Assert(VirtualTransactionIdIsValid(vxid));
SET_LOCKTAG_VIRTUALTRANSACTION(tag, vxid);
(void) LockAcquire(&tag, ExclusiveLock, false, false);
}
/*
* VirtualXactLockTableWait
*
* Waits until the lock on the given VXID is released, which shows that
* the top-level transaction owning the VXID has ended.
*/
void
VirtualXactLockTableWait(VirtualTransactionId vxid)
{
LOCKTAG tag;
Assert(VirtualTransactionIdIsValid(vxid));
SET_LOCKTAG_VIRTUALTRANSACTION(tag, vxid);
(void) LockAcquire(&tag, ShareLock, false, false);
LockRelease(&tag, ShareLock, false);
}
/*
* ConditionalVirtualXactLockTableWait
*
* As above, but only lock if we can get the lock without blocking.
* Returns TRUE if the lock was acquired.
*/
bool
ConditionalVirtualXactLockTableWait(VirtualTransactionId vxid)
{
LOCKTAG tag;
Assert(VirtualTransactionIdIsValid(vxid));
SET_LOCKTAG_VIRTUALTRANSACTION(tag, vxid);
if (LockAcquire(&tag, ShareLock, false, true) == LOCKACQUIRE_NOT_AVAIL)
return false;
LockRelease(&tag, ShareLock, false);
return true;
}
/*
* This is the main executioner for any query backend that conflicts with
* recovery processing. Judgement has already been passed on it within
* a specific rmgr. Here we just issue the orders to the procs. The procs
* then throw the required error as instructed.
*/
static void
ResolveRecoveryConflictWithVirtualXIDs(VirtualTransactionId *waitlist,
ProcSignalReason reason)
{
TimestampTz waitStart;
char *new_status;
/* Fast exit, to avoid a kernel call if there's no work to be done. */
if (!VirtualTransactionIdIsValid(*waitlist))
return;
waitStart = GetCurrentTimestamp();
new_status = NULL; /* we haven't changed the ps display */
while (VirtualTransactionIdIsValid(*waitlist))
{
/* reset standbyWait_us for each xact we wait for */
standbyWait_us = STANDBY_INITIAL_WAIT_US;
/* wait until the virtual xid is gone */
while (!ConditionalVirtualXactLockTableWait(*waitlist))
{
/*
* Report via ps if we have been waiting for more than 500 msec
* (should that be configurable?)
*/
if (update_process_title && new_status == NULL &&
TimestampDifferenceExceeds(waitStart, GetCurrentTimestamp(),
500))
{
const char *old_status;
int len;
old_status = get_ps_display(&len);
new_status = (char *) palloc(len + 8 + 1);
memcpy(new_status, old_status, len);
strcpy(new_status + len, " waiting");
set_ps_display(new_status, false);
new_status[len] = '\0'; /* truncate off " waiting" */
}
/* Is it time to kill it? */
if (WaitExceedsMaxStandbyDelay())
{
pid_t pid;
/*
* Now find out who to throw out of the balloon.
*/
Assert(VirtualTransactionIdIsValid(*waitlist));
pid = CancelVirtualTransaction(*waitlist, reason);
/*
* Wait a little bit for it to die so that we avoid flooding
* an unresponsive backend when system is heavily loaded.
*/
if (pid != 0)
pg_usleep(5000L);
}
}
/* The virtual transaction is gone now, wait for the next one */
waitlist++;
}
/* Reset ps display if we changed it */
if (new_status)
{
set_ps_display(new_status, false);
pfree(new_status);
}
}
