Have you ever seen this?
Have you ever seen a message like this while working with ORDS? The one where you receive a 503 Service Unavailable response code and message?
This message has something to do with ORDS being unable to make a connection to the database.
But if you keep reading, you’ll see even more information- something related to the Universal Connection Pool- followed by an array of numbers. Did you know that the “stuff” in that array is actually helpful information?
Well…Kris knew.
What does it all mean?
But for the rest of us plebes, what does “max = 30 and current in use = 30” refer to? Well, let’s figure it out!
Take a closer look at the above image. You’ll see an array consisting of the following: [30, 30, 42, 12, 0, 30, 1, 0, 29]. Which, according to the Universal Connection Pool documentation, translates to:
Now what?
So, what do we do with this information? Well, it depends. In this case, it looks like available connections were exhausted. And what could cause that? It’s a mystery, but it doesn’t have to be 😉. You need to do some exploring (It’s not just going to fix itself.)!
Luckily, there are many ways to “peek under the covers” to learn what is happening in and around your database. Some things that come to mind:
- Access and debug logging at the ORDS level
- AWR reports from/in the database
- V$SESSION, along with the other Dynamic Performance Views available in the Oracle database
These are the ones that I’m most familiar. But if you are reading this, what works for you? Drop a comment on what tools you use, and I’ll update this post for others to see!
When you’re ready…
Once you’ve determined what is happening, you can return to ORDS and tweak your JDBC settings—if you need to!
BIG DISCLAIMER: I wouldn't just set your Max connection settings to some arbitrarily high number. That might work in the short term. But until you can figure out what is actually happening across an application's execution path, that approach is just a band-aid solution.
That’s all folks
This post is outside the norm of what I usually post. I’m not doing a walkthrough or tutorial. I’m just…throwing some info out there. I mainly wanted to write this quick PSA before I forgot.
I’ve seen this error come up frequently in questions. I think if more people knew what those numbers meant, it might help with self-diagnosis. I hope I’m not wrong. Catch you later 😎!
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