This cache can serve invalid responses, and has an extremely low hit
rate.
It serves invalid responses because because it's only keyed off
the `since` parameter, but many of the other request parameters also
affect the response or it's side effects. This will become worse once we
implement filtering, because there will be a wider space of parameters
with different responses. This problem is fixable, but not worth it
because of the low hit rate.
The low hit rate is because normal clients will always issue the next
sync request with `since` set to the `prev_batch` value of the previous
response. The only time we expect to see multiple requests with the same
`since` is when the response is empty, but we don't cache empty
responses.
This was confirmed experimentally by logging cache hits and misses over
15 minutes with a wide variety of clients. This test was run on
matrix.computer.surgery, which has only a few active users, but a
large volume of sync traffic from many rooms. Over the test period, we
had 3 hits and 5309 misses. All hits occurred in the first minute, so I
suspect that they had something to do with client recovery from an
offline state. The clients that were connected during the test are:
- element web
- schildichat web
- iamb
- gomuks
- nheko
- fractal
- fluffychat web
- fluffychat android
- cinny web
- element android
- element X android
Fixes: #336
Hardcoding the output path to something in CWD is a pain if you're running
conduwuit through systemd or similar. Also made the error message when
it's unable to create the output file a little more friendly.
Previously, enabling the `tracing_flame` or `allow_jaeger` options would
prevent any logs from being written to stdout. In addition, enabling the
`allow_jaeger` option would inhibit the `tracing_flame` option.
Now that we have a way to use separate tracing filters with different
layers, we can enable all three at the same time without issues.
This commit also prevents the `debug log_level` command from modifying
the `tracing-flame` filter. This was supported previously, but I don't
think it's something that you would ever want to do intentionally. Now
that we have both the normal log filter and the `tracing-flame` filter
enabled at the same time, we want to `debug log_level` to only modify the
normal filter.
This turned out to be quite hairy, mostly because we need to apply the
config's log level filter to the actual logs (stdout and, optionally
sentry), but do not want to filter out the tokio tracing events needed by
the console_subscriber. I hit several edge cases in tracing getting
this to work, and we now depend on a git version of tracing with a
backported patch :(
Benjamin Lee