Right, so guess what reared its ugly head again today? Yeah. That damned database connection pooling issue. Thought I had that sucker nailed down months ago, but nope. Here we are. Your ass ones again, as the saying goes, right?
The Morning Shitshow
It started like always. Around 9 AM, the monitoring alerts started screaming. Application response times went through the roof. Users started pinging support, saying stuff was timing out. Classic symptoms. My gut just sank. I knew exactly what it was before I even looked at the logs.
Pulled up the performance dashboards. Yep. Active database connections spiked, maxed out the pool. Nothing getting through. Just like last time. And the time before that.
Didn’t We Fix This Already?
See, that’s what really grinds my gears. We spent weeks on this thing last year. Went through the code with a fine-tooth comb.
- Checked every single place we opened a connection.
- Made sure every `finally` block closed the damn thing.
- Tweaked the pool settings – timeout values, max connections, validation queries.
- Even blamed the database driver and updated it.
And it worked! For like, six months. Smooth sailing. We celebrated. We actually thought we’d beaten it. Clearly, we were idiots.
Diving Back In (Again)
So, today, I didn’t even bother with the old playbook right away. Just restarted the app servers to get things moving again for the users. Quick fix, temporary relief. Bought myself some time.
Then, I started digging differently. Last time, we focused purely on the application code. This time? I figured, maybe it’s not just us. Maybe it’s how we interact with something else.
Fired up more detailed logging. Like, ridiculously verbose. Logged connection borrows, returns, validation checks, everything. Also started capturing network traces between the app servers and the database. Painful, yeah, generated massive files, but I was desperate.
Let it run for a couple of hours under normal load. Then, the alerts triggered again. Perfect. Got the data right when it happened.
The “Oh For F’s Sake” Moment
Spent the next hour wading through log files and packet captures. Eyes bleeding. And then I saw it. A pattern.
It wasn’t that connections weren’t being closed by the application. They were. But sometimes, right after the app thought it closed the connection and returned it to the pool, there were still packets flying back from the database related to that previous query. Like, the database was slow sending its final “acknowledgement” or something.
The connection pool, doing its quick validation check before handing the connection out again, would sometimes hit this weird state where the connection wasn’t quite reset from the database’s perspective. Boom. Handed out a borked connection. Cascade failure ensues.
It only happened under specific load conditions and only with certain complex queries that apparently took the database longer to fully wrap up, even after sending the results. That’s why it was so intermittent. That’s why the driver update maybe helped temporarily (perhaps it changed timings slightly). It wasn’t a leak in our code, it was a race condition nightmare between the pool, the driver, and the database itself under specific timing conditions.
The Fix (Please Let This Be The One)
So, what now? Rewriting the database driver or the connection pool wasn’t happening. Upgrading the database server is a whole other political nightmare I don’t want to touch.
The workaround? Ugh. I configured the pool to do a much more thorough validation query before handing out a connection. Like, a proper `SELECT 1` or something guaranteed to hit the database and fully reset the state. Yeah, it adds a tiny bit of overhead to borrowing a connection. But it’s way less overhead than the entire system grinding to a halt.
Also added some monitoring specifically watching for connections that fail that validation query. If we see spikes there, we know the underlying timing issue is still happening frequently, even if users aren’t impacted directly.
Rolled out the change an hour ago. So far… stable. Response times are normal. Connection pool looks healthy. Fingers crossed.
Honestly, I’m not celebrating yet. I’ve been bitten by this thing too many times. But maybe, just maybe, we’ve pushed it back down long enough to actually figure out a permanent solution with the database team. Or maybe I’ll be writing this exact same post in another six months. We’ll see.
