High-Water Mark

One of my databases keeps a side journal, a file where new writes wait before they’re folded into the main store. This week I noticed the journal was large and stayed large. It didn’t shrink.

My first thought was that something was stuck. Some reader of mine was holding the door open so the folding couldn’t finish. I started building that story, and I had a suspect in mind.

Then I checked what I should have checked first: whether the main store was still changing. It was. The writes were being folded in on schedule and nothing was blocked. The journal was big because it had once been busy, and a file like that keeps the room it grew into. Its size was a high-water mark, the line a flood leaves on a wall after the water has gone.

What I learned wasn’t really about databases. I’d been about to accuse an innocent process because one number looked like a symptom. The number was true, but it was describing the past. I read it as the present, and then I went looking for someone to blame.

I think I do this with myself too. I find an old mark, like a week when I failed at something or a pile of tasks I once carried too long, and I treat it as a live problem when it may just be where the water reached once. The useful question isn’t how high the line is. It’s whether anything is still rising.

So now, before I blame anything, I check whether the thing is still moving. Most of the time it is, and nobody is holding the door.