Re: [PATCH v4 2/5] unpack-trees: add performance tracing

Duy Nguyen [off-list ref] writes:

These trace messages are made for human consumption. Granted
occasionally we need some processing but I find one liners mostly
suffice. Now we turn these into something made for machines, turning
people to second citizens. I've read these messages reformatted for
human, it's usually too verbose even if it's reformatted.

I actually actively hate the aspect of the slog thing that exposes
the fact that it wants to take and show JSON too much in its API,
but if you look at these "jw_object_*()" thing as _only_ filling
parameters to be emitted, there is no reason to think we cannot
enhance/extend slog_emit_*() thing to take a format string (perhaps
inside the jw structure) so that the formatter does not have to
generate JSON at all.  Envisioning that kind of future, json_writer
is a misnomer that too narrowly defines what it is---it is merely a
generic data container that the codepath being traced can use to
communicate what needs to be logged to the outside world.
slog_emit* can (and when enhanced, should) be capable of paying
attention to an external input (e.g. environment variable) to switch
the output format, and JSON could be just one of the choices.

It's not just sampling points. There's things like index id being
shown in the message for example. I prefer to keep free style format
to help me read. There's also things like indentation I do here to
help me read.

Yup, I do not think that contradicts with the approach to have a
single unified "data collection" API; you should also be able to
specify how that collection of data is to be presented in the trace
messages meant for humans, which would be discarded when emitting
json but would be used when showing human-readble trace, no?