Re: Frequent 'deadlock detected' in 7.4 ... or just my bad

D'oh ... just tested my assumption, it was wrong ... *sigh* okay, back
to the drawing board on the code ...

On Mon, 5 Apr 2004, Marc G. Fournier wrote:

> On Mon, 5 Apr 2004, Tom Lane wrote:
>
> > "Marc G. Fournier" <scrappy(at)postgresql(dot)org> writes:
> > > Now, the scripts are wrap'd in a BEGIN/END ... if a file fails to be
> > > loaded, I want the whole thing to rollback ... the deadlock itself, I'm
> > > presuming, is because two servers are trying to update the same
> > > $ip_id/$port/$company_id record, at the same time ...
> >
> > Actually, the problem is more likely that two servers try to update two
> > different rows in opposite orders. It's not possible to deadlock when
> > only one lock is involved.
> >
> > You could work around this by ensuring that all sessions update rows in
> > a consistent order; for instance, at the beginning of a transaction sort
> > your intended updates by primary key and then apply in that order.
>
> Actually, unless I'm mistaken about how hashes work in perl, the update
> order for all servers is the same ... basically what happens is:
>
> 1. a traffic table is read in, and loaded into a hash table that is
> ordered by company_id, ip_id and port:
>
> $traffic{$ip_rec{$ip}{'company_id'}}{$ip_id}{$port} += $bytes1 + $bytes2;
>
> 2. a foreach loop is run on that resultant list to do the updates to the
> database:
>
> foreach $company_id ( keys %traffic ) {
> foreach $ip_id ( keys %{$traffic{$company_id}} ) {
> foreach $port ( keys %{$traffic{$company_id}{$ip_id}} ) {
>
> and the updates are done based on those 3 values, plus the byte value
> of $traffic{$company_id}{$ip_id}{$port} ...
>
> Now, my first mistake may be that I'm mis-assuming that the hashes will
> be read in a sorted order ... ? If this is the case, though, then sort
> order shouldn't be an issue, as all servers would be sorted the same way
> ...
>
>
>
> ----
> Marc G. Fournier Hub.Org Networking Services (http://www.hub.org)
> Email: scrappy(at)hub(dot)org Yahoo!: yscrappy ICQ: 7615664
>

----
Marc G. Fournier Hub.Org Networking Services (http://www.hub.org)
Email: scrappy(at)hub(dot)org Yahoo!: yscrappy ICQ: 7615664