Actually, on further thought, there's a really simple solution that
we've used elsewhere: make sure you have the resource you need *before*
you get into the critical section of code. I've applied the attached
revised patch.

regards, tom lane

*** src/backend/storage/lmgr/lwlock.c.orig Fri Dec 31 17:46:10 2004
--- src/backend/storage/lmgr/lwlock.c Fri Apr 8 10:14:04 2005
***************
*** 213,218 ****
--- 213,222 ----
*/
Assert(!(proc == NULL && IsUnderPostmaster));

+ /* Ensure we will have room to remember the lock */
+ if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
+ elog(ERROR, "too many LWLocks taken");
+
/*
* Lock out cancel/die interrupts until we exit the code section
* protected by the LWLock. This ensures that interrupts will not
***************
*** 328,334 ****
SpinLockRelease_NoHoldoff(&lock->mutex);

/* Add lock to list of locks held by this backend */
- Assert(num_held_lwlocks < MAX_SIMUL_LWLOCKS);
held_lwlocks[num_held_lwlocks++] = lockid;

/*
--- 332,337 ----
***************
*** 353,358 ****
--- 356,365 ----

PRINT_LWDEBUG("LWLockConditionalAcquire", lockid, lock);

+ /* Ensure we will have room to remember the lock */
+ if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
+ elog(ERROR, "too many LWLocks taken");
+
/*
* Lock out cancel/die interrupts until we exit the code section
* protected by the LWLock. This ensures that interrupts will not
***************
*** 397,403 ****
else
{
/* Add lock to list of locks held by this backend */
- Assert(num_held_lwlocks < MAX_SIMUL_LWLOCKS);
held_lwlocks[num_held_lwlocks++] = lockid;
}

--- 404,409 ----

---------------------------(end of broadcast)---------------------------
TIP 4: Don't 'kill -9' the postmaster

"Tom Lane" <tgl@sss.pgh.pa.us> writes
> Actually, on further thought, there's a really simple solution that
> we've used elsewhere: make sure you have the resource you need *before*
> you get into the critical section of code. I've applied the attached
> revised patch.
>

Oh, that's the one - why didn't think of it at the first time? :-)

Regards,
Qingqing