http://www.slony.info/bugzilla/show_bug.cgi?id=273

           Summary: Slon can try to pull data from a behind provider.
           Product: Slony-I
           Version: devel
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: low
         Component: slon
        AssignedTo: slony1-bugs at lists.slony.info
        ReportedBy: ssinger at ca.afilias.info
                CC: slony1-bugs at lists.slony.info
   Estimated Hours: 0.0


In master/2.2 I've been getting the occasional failure of one of the disorder
tests ('merge set', before any set merging takes place).  What happens is one
of the subscriber nodes (often node 3) will try to pull data in sync_event from
a node that is not the provider or origin (often node 5).  This node is too far
behind so the sync fails.

I had attached with gdb and saw that the wd->provider chain contains two nodes,
a) The origin node 1 and b) the node that it was not far enough behind.  The
SYNC event it is processing comes from event_provider=1

The adjust_provider_info function seems to process some event that came from
listener 5. It logs the following:

just after the subscription to set 1 finishes.

2012-06-28 15:40:34,803 [db3 stdout] DEBUG . - 2012-06-28 15:40:34 EDT CONFIG
remoteWorkerThread_1: added active set 1 to provider 1
2012-06-28 15:40:34,803 [db3 stdout] DEBUG . - 2012-06-28 15:40:34 EDT CONFIG
remoteWorkerThread_1: added event provider provider 5

The 'added event provider provider 5' is debugging I added to the if block in
'step 4' of adjust_provider info.

What I *suspect* is happening is that
* Node 3 is not yet subscribed to any sets
* remoteListener_5 on node 3 queues up the subscription events and a SYNC event
from node 1
* The subscription finishes
* adjust_provider_info is called it adds node 1 as a provider since it is the
origin of the set.  It also adds node 5 as a provider since it is where the
event was received from (step 4).
* We process the SYNC event from node 1.

In sync_event we expect BOTH of those providers in the provider list (1 and 5)
to be far enough ahead.

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