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When Oracle SOA Database Pollers Collide by Aaron Dolan

Juergen Kress
PaaS Partner Adoption

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Oracle SOA Database Adapters provide a polling mechanism that will periodically query a table to see if a there is a new or changed record.  If so, it can trigger a BPEL process.  This is enormously useful.  However, on one client I ran into a series of issues with database pollers in a clustered environment when they … collided.  (queue dramatic music)

The issue began one quiet morning early in the project after I started my WebLogic Admin Server and 2 SOA 11g Managed Servers.  I then deployed my process with my shiny new database poller.  I was very excited to see it work in the Development Environment.  I had tested it the night before in my local VM and it worked great.

I won’t bore you with the details of what the overall process did, but suffice it to say, I was not excited with the database error I received when the pollers fired.  You heard me right … pollers.

I did NOT anticipate that SOA would have a separate database poller for each managed server for the same process.  However, after consulting with colleagues, I found that they too had seen this rather odd and seemingly illogical behavior.

Luckily after a bit of sleuthing, I found a nice solution – the Distributed Polling flag.  As usual, the A Team came to the rescue with an outstanding article that nicely explained the inner guts of how this works: DB Adapter – Distributed Polling (SKIP LOCKED) Demystified.

In short, this flag doesn’t allow more than 1 server to issue a lock on a table at a given time.  In effect, this ensures that you end up with 1 database poller for your process and not 1 per managed server (however, there is a twist to this that I’ll discuss in a moment). Read the complete article here.

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