I have a standard transaction group with the sole purpose of executing a query tag at the top of the hour. I know there are similar posts asking how to accomplish this. That is not the question, not looking for suggestions for schedule based and so-on, simply want to know why this setup fails to execute ~1 out of 100 hours. I have this same setup on 2 servers across 5 projects. It has been running for 5+ years, no one noticed the random failures until recently when we missed 4 executions back-to-back, enough to create gaps in the plot that displays this data, alerting my clients to the issue. After exhausting all options that explain this failure as a new problem, I went back 8 years, and found missed execution had been occuring since start-up. This spans multiple ignition versions, java builds, server settings etc.
Execution Scheduling: Timer, 1 minute(s)
Execute this group on Trigger
Only execute once while trigger is active
Trigger conditions - is = 0 (or false)
Expression tag, run always
1 triggered expression item which runs an insert into select. The query takes less than 100ms to run.
For testing purposes, I set up the exact same group, only I stored the value of the minute extract along with the current timestamp. Instead of executing on trigger = 0, I executed on trigger value change. I let this run for 12 hours. I didn’t have a single disagreement between the dateextract and the timestamp, but I did miss around 1 out of every 100 minutes, on both servers across all projects.
Very simple problem, yet after 3 rounds with tech support, no one can offer an explanation. No clock drifts, no server issues, no db/server sync issues. When I look at it from a DSP perspective, this group ‘undersamples’ the trigger tag (looking for a change in minute, only once a minute). But I am assured that without clock drifts, this shouldn’t miss.
Any thoughts? Not a big deal for this particular dataset, but highly concerning given the failure rate I have observed.