conduwuit/docs/troubleshooting.md

# Troubleshooting conduwuit

> ## Docker users ⚠️
>
> Docker is extremely UX unfriendly. Because of this, a ton of issues or support
> is actually Docker support, not conduwuit support. We also cannot document the
> ever-growing list of Docker issues here.
>
> If you intend on asking for support and you are using Docker, **PLEASE**
> triple validate your issues are **NOT** because you have a misconfiguration in
> your Docker setup.
>
> If there are things like Compose file issues or Dockerhub image issues, those
> can still be mentioned as long as they're something we can fix.

## General potential issues

#### Potential DNS issues when using Docker

Docker has issues with its default DNS setup that may cause DNS to not be
properly functional when running conduwuit, resulting in federation issues. The
symptoms of this have shown in excessively long room joins (30+ minutes) from
very long DNS timeouts, log entries of "mismatching responding nameservers",
and/or partial or non-functional inbound/outbound federation.

This is **not** a conduwuit issue, and is purely a Docker issue. It is not
sustainable for heavy DNS activity which is normal for Matrix federation. The
workarounds for this are:
- Use DNS over TCP via the config option `query_over_tcp_only = true`
- Don't use Docker's default DNS setup and instead allow the container to use
and communicate with your host's DNS servers (host's `/etc/resolv.conf`)

## Rocksdb / database issues

#### Direct IO

Some filesystems may not like RocksDB using [Direct
IO](https://github.com/facebook/rocksdb/wiki/Direct-IO). Direct IO is for
non-buffered I/O which improves conduwuit performance, but at least FUSE is a
filesystem potentially known to not like this. See the [example
config](configuration/examples.md) for disabling it if needed. Issues from
Direct IO on unsupported filesystems are usually shown as startup errors.

#### Database corruption

If your database is corrupted *and* is failing to start (e.g. checksum
mismatch), it may be recoverable but careful steps must be taken, and there is
no guarantee it may be recoverable.

The first thing that can be done is launching conduwuit with the
`rocksdb_repair` config option set to true. This will tell RocksDB to attempt to
repair itself at launch. If this does not work, disable the option and continue
reading.

RocksDB has the following recovery modes:

- `TolerateCorruptedTailRecords`
- `AbsoluteConsistency`
- `PointInTime`
- `SkipAnyCorruptedRecord`

By default, conduwuit uses `TolerateCorruptedTailRecords` as generally these may
be due to bad federation and we can re-fetch the correct data over federation.
The RocksDB default is `PointInTime` which will attempt to restore a "snapshot"
of the data when it was last known to be good. This data can be either a few
seconds old, or multiple minutes prior. `PointInTime` may not be suitable for
default usage due to clients and servers possibly not being able to handle
sudden "backwards time travels", and `AbsoluteConsistency` may be too strict.

`AbsoluteConsistency` will fail to start the database if any sign of corruption
is detected. `SkipAnyCorruptedRecord` will skip all forms of corruption unless
it forbids the database from opening (e.g. too severe). Usage of
`SkipAnyCorruptedRecord` voids any support as this may cause more damage and/or
leave your database in a permanently inconsistent state, but it may do something
if `PointInTime` does not work as a last ditch effort.

With this in mind:

- First start conduwuit with the `PointInTime` recovery method. See the [example
config](configuration/examples.md) for how to do this using
`rocksdb_recovery_mode`
- If your database successfully opens, clients are recommended to clear their
client cache to account for the rollback
- Leave your conduwuit running in `PointInTime` for at least 30-60 minutes so as
much possible corruption is restored
- If all goes will, you should be able to restore back to using
`TolerateCorruptedTailRecords` and you have successfully recovered your database

## Debugging

Note that users should not really be debugging things. If you find yourself
debugging and find the issue, please let us know and/or how we can fix it.
Various debug commands can be found in `!admin debug`.

#### Debug/Trace log level

conduwuit builds without debug or trace log levels by default for at least
performance reasons. This may change in the future and/or binaries providing
such configurations may be provided. If you need to access debug/trace log
levels, you will need to build without the `release_max_log_level` feature.

#### Changing log level dynamically

conduwuit supports changing the tracing log environment filter on-the-fly using
the admin command `!admin debug change-log-level`. This accepts a string
**without quotes** the same format as the `log` config option.

#### Pinging servers

conduwuit can ping other servers using `!admin debug ping`. This takes a server
name and goes through the server discovery process and queries
`/_matrix/federation/v1/version`. Errors are outputted.

#### Allocator memory stats

When using jemalloc with jemallocator's `stats` feature, you can see conduwuit's
jemalloc memory stats by using `!admin debug memory-stats`