Whenever we start processing a request, we now enter a tracing "span"
that includes context information like the tenant and timeline ID, and
the operation we're performing. That context information gets attached
to every log message we create within the span. That way, we don't need
to include basic context information like that in every log message, and
it also becomes easier to filter the logs programmatically.
This removes the eplicit timeline and tenant IDs from most log messages,
as you get that information from the enclosing span now.
Also improve log messages in general, dialing down the level of some
messages that are not very useful, and adding information to others.
We now obey the RUST_LOG env variable, if it's set.
The 'tracing' crate allows for different log formatters, like JSON or
bunyan output. The one we use now is human-readable multi-line format,
which is nice when reading the log directly, but hard for
post-processing. For production, we'll probably want JSON output and
some tools for working with it, but that's left as a TODO. The log
format is easy to change.
This contains a lowest common denominator of pageserver and safekeeper log
initialisation routines. It uses daemonize flag to decide where to
stream log messages. In case daemonize is true log messages are
forwarded to file. Otherwise streaming to stdout is used. Usage of
stdout for log output is the default in docker side of things, so make
it easier to browse our logs via builtin docker commands.
