💾 Archived View for gemini.ctrl-c.club › ~stack › gemlog › 2023-06-26.tailf.gmi captured on 2023-07-10 at 13:49:47. Gemini links have been rewritten to link to archived content

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hottail -- tail -f with a heat-map

I am a big fan of log files. As I develop and test, and deploy code, logs provide invaluable information for debugging and improving (and sometimes, understanding) the system.

While watching logs with 'tail -f' works pretty well, I would _really_ like to see a heat-mapped view of a log. By that I mean colorized lines which start hot and slowly cool -- allowing me to instantly see if anything happened recently, as well as the relative age of entries -- at a glance!

I assumed that anything I can think someone has already done -- the world is now big enough for that. But it appears that no one has, in this case. There are many ways to colorize a log based on its content, but not time-based.

If you know of something like that, please email stack@ctrl-c.club.

Maybe I'll do it myself?

My crocodile brain started coding before I even finished the first search... It's an interesting problem (as I get older I find all problems interesting)... There are some curious edge cases that can really screw you:

A log may be rotated or wiped, so caching state (required for color-mapping against time) is tricky;
A log may not be a log - something can write random data in the middle!
A line may not be finished writing when sampled!
I need to correllate between reads to age older lines - kind of an interesting sliding window problem...
I need to either be notified of file changes or sample file size efficiently enough.

So I could read the tail -n- bytes into a buffer and scan backwards for line ends, entering them into an index (along with a timestamp). Later, if a change is detected (say, filesize changed), I can re-read, and scan again, but in a more complicated way, against the old index:

New data is just scanned with new timestamp;
Old data must match the index, timestamp copied;
Mismatch indicates a log rotation; dump old data;
Except a mismatch in the final line-end of old log may mean a partially-written line and is not an error.

A redisplay task should assign colors based on age, and reprint the required lines. This should be configurable...

Configuration: parameters (ugh), mapping strategy, adjusting time and color at runtime, etc.

Maybe worth a few days of coding, since I have nothing better to do. I want to say a day, but I know better.

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