Re: [HACKERS] Table locking ...

Okay, I did find a LOCK being issued, just not sure if its required or
not, with MVCC...

On Sat, 8 Jan 2000, The Hermit Hacker wrote:

> 
> I'm seeing a weird problem, that I don't think I should be expecting in
> v6.5.3 of PostgreSQL ... an inability to SELECT form a database while the
> UdmSearch/indexer is running...
> 
> ps shows:
> 
> 30040  ??  R     20:54.37 /home/database/v6.5.3/bin/postgres pgsql 216.126.84.1 udmsearch UPDATE
> 43846  ??  I      0:00.03 /home/database/v6.5.3/bin/postgres pgsql 216.126.84.1 udmsearch SELECT waiting
> 
> And, if I do successive ps's in a row, the 'SELECT waiting' stays, but the
> UPDATING keeps flashing between 'UPDATING' and 'idle'...
> 
> *Eventually*, the SELECT gets perform and the call returns...
> 
> But, with MVCC, I didn't think that I should see any 'hangs' on SELECT
> calls...the process on 43846 is 'indexer -S', which just generates stats
> on the database.
> 
> The problem, in the case of this particular application, is that if
> multiple searches were to happen, while the database is being updated, it
> seems that this could be a point of contention?
> 
> >From what I can tell reading through the reading through the code, there
> is never a TABLE LOCK issued when using PostgreSQL, but it does use
> BEGIN/END...
> 
> Am I misunderstanding how MVCC is supposed to work?  Could we have a bug
> in v6.5.3?
> 
> I'm still looking through the code, to see if I've overlooked something,
> but I figure I'd check to see if maybe I'm misunderstanding MVCC
> altogether first...
> 
> I'm CCng in the author of the code, just in case this is something that
> I'm overlooking in theh code...
> 
> Marc G. Fournier                   ICQ#7615664               IRC Nick: Scrappy
> Systems Administrator @ hub.org 
> primary: scrappy@hub.org           secondary: scrappy@{freebsd|postgresql}.org 
> 
> 
> ************
> 

Marc G. Fournier                   ICQ#7615664               IRC Nick: Scrappy
Systems Administrator @ hub.org 
primary: scrappy@hub.org           secondary: scrappy@{freebsd|postgresql}.org