Alvaro Herrera <[EMAIL PROTECTED]> writes:
> I'm cooking a patch for this which seems pretty reasonable, but I'm
> having a problem: what mechanism do we have for waiting until a process
> exits?
None, and I think you probably don't want to sit on the database lock
while waiting, either. I was envisioning a simple sleep loop, viz
for(;;)
{
acquire database lock;
foreach(PGPROC entry in that database)
{
if (it's autovac)
send sigint;
else
fail;
}
if (found any autovacs)
{
release database lock;
sleep(100ms or so);
/* loop back and try again */
}
else
break;
}
Also see Peter's nearby suggestion that we ought to wait instead of fail
for *all* cases of somebody attached to the database. This would adapt
readily enough to that.
I was complaining elsewhere that I didn't want to use a sleep loop
for fixing the fsync-synchronization issue, but CREATE/DROP DATABASE
seems a much heavier-weight operation, so I don't feel that a sleep
is inappropriate here.
> Maybe make autovacuum acquire an LWLock at start, which it then
> keeps until it's gone, but it seems wasteful to have a lwlock just for
> that purpose.
And it doesn't scale to multiple autovacs anyway, much less the wait-for-
everybody variant.
regards, tom lane
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