# logfmt for PostgreSQL

Format PostgreSQL logs as [logfmt](https://brandur.org/logfmt).

logfmt is a log style designed by Heroku.
It's a compact way of presenting untyped structured log, easier for human to read and for machine to marshal.
logfmt is now a best practice in Grafana/Loki and kubernetes world.

```
ts=2023-05-25T10:01:50.992+0200 level=LOG message="checkpoint starting: time"
ts=2023-05-25T10:01:50.992+0200 level=LOG message="checkpoint complete: wrote 15 buffers (0.1%); 0 WAL file(s) added, 0 removed, 0 recycled; write=1.215 s, sync=0.008 s, total=1.236 s; sync files=13, longest=0.005 s, average=0.001 s; distance=63 kB, estimate=63 kB; lsn=0/1CB7BA0, redo lsn=0/1CB7B68"
```


## Build and Installation from Source

For now, logfmt is only available through git.

- Get the source code using git.
- Setup your PATH with `pg_config` for the target PostgreSQL version.
- Type `make` to build.
- Type `make install` to install.

logfmt is known to work with PostgreSQL 16beta1.


## Enable logfmt

- Add `logfmt` to `shared_preload_libraries`.
- Restart PostgreSQL.


## Parameter

The `logfmt.application_context` parameter allows you to set an application-centric tag to group log entries.
For example, set it to the UUID of a web request or a background task.


## Fields

logfmt has opininated field names
based on regular logfmt fields
and on elog and jsonlog PostgreSQL fields.
logfmt respects `log_error_verbosity` parameter.

Terse fields:

- `application_name` and `application_context`
- `dbname`
- `level` - Error severity.
- `message`
- `pid` - Postgres process identifier.
- `statement`, `statement.position`
- `ts` - Log timestamp with millisecond and timezone offset.
- `user`


Default fields:

- `remote.host`, `remote.port`
- `context`
- `detail`
- `hint`
- `xid`, `vxid`
- `internal.query`, `internal.position`
- `backend_type`
- `leader.pid`
- `statement.qid` - pg_stat_statement query ID.

Verbose fields:

- `backtrace`
- `errcode` - SQL error code.
- `location.file`, `location.line`, `location.func`


Output order is hard coded.


## About

logfmt is a PostgreSQL extension initiated by Dalibo.