Avoid duplicate peers for no-direct and maybe-direct forwarding

Hello,

    While trying to configure Squid to resend the request to the second
cache_peer if the first one fails, I noticed that the first peer is
tried twice:

  # this peer will be tried twice in a row:
  cache_peer 172.16.101.151 parent 80 0 originserver no-query
  # then this peer will be tried
  cache_peer 172.16.103.151 parent 80 0 originserver no-query
  # this is required to allow retries
  retry_on_error on

I believe the first peer is accessed twice because it is added twice to
the list of possible peers. Here is the peerSelectFoo() code that adds
the same peer twice because peerGetAllParents() is called after
peerGetSomeParent():

> case DIRECT_NO:
> peerGetSomeParent(ps);
> peerGetAllParents(ps);
> break;
>
> default:
...
> if (request->flags.hierarchical || !Config.onoff.nonhierarchical_direct) {
> peerGetSomeParent(ps);
> peerGetAllParents(ps);
> }

I hit the maybe-direct case in my tests, but the no-direct case seems to
have the same flaw. The peer failure I am simulating is a 403 Forbidden
response, but it probably does not matter.

Assuming it is wrong to add (and then use) the same parent twice for the
same request (because it screws up retries and such), we have a few options:

1. Change peerGetAllParents() so that only new parents are added. This
will fix my use case, but there could be other cases where we add
duplicate peers -- I see other conditional peerGet*() calls before and
after the ones quoted above. It may be difficult to avoid duplicates
under all conditions.

2. Change lower-level peerAddFwdServer() so that only new servers are
added even if the higher level code tries to add duplicates; the "same
server" comparison can be done using server address (including port) and
disregarding the hierarchy code. This will fix my use case, but I am not
100% sure whether skipping some servers would break some configurations
because those servers have "more important" hierarchy code, even though
they are added later/last.

Should I do #2? Is there a better option?

Thank you,

Alex.
Received on Sun Apr 29 2012 - 04:50:29 MDT