When Oracle SOA Database Pollers Collide by Aaron Dolan

April 4, 2018 Leave a comment

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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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Unknown's avatarAbout Jürgen Kress
As a middleware expert Jürgen works at Oracle EMEA Alliances and Channels, responsible for Oracle’s EMEA Fusion Middleware partner business. He is the founder of the Oracle SOA & BPM and the WebLogic Partner Communities and the global Oracle Partner Advisory Councils. With more than 5000 members from all over the world the Middleware Partner Community is the most successful and active community at Oracle. Jürgen manages the community with monthly newsletters, webcasts and conferences. He hosts his annual Fusion Middleware Partner Community Forums and the Fusion Middleware Summer Camps, where more than 200 partners get product updates, roadmap insights and hands-on trainings. Supplemented by many web 2.0 tools like twitter, discussion forums, online communities, blogs and wikis. For the SOA & Cloud Symposium by Thomas Erl, Jürgen is a member of the steering board. He is also a frequent speaker at conferences like the SOA & BPM Integration Days, JAX, UKOUG, OUGN, or OOP.

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