Adds all bool/integer/real runtime variables that can be retrieved ths way.
Use the `pg_settings` view to retrieve runtime variables:
https://www.postgresql.org/docs/current/static/view-pg-settings.html
Replaces the use of `SHOW` to retrieve runtime variables.
Only runtime variables with a `vartype` of `bool`, `real`, or `integer`
are currently supported. Uses the `short_desc` field as a description.
This commit deprecates the following metric names:
```
pg_runtime_variable_max_connections
pg_runtime_variable_max_files_per_process
pg_runtime_variable_max_function_args
pg_runtime_variable_max_identifier_length
pg_runtime_variable_max_index_keys
pg_runtime_variable_max_locks_per_transaction
pg_runtime_variable_max_pred_locks_per_transaction
pg_runtime_variable_max_prepared_transactions
pg_runtime_variable_max_standby_archive_delay_milliseconds
pg_runtime_variable_max_standby_streaming_delay_milliseconds
pg_runtime_variable_max_wal_senders
```
They are replaced by equivalent names under `pg_settings` with the exception of
```
pg_runtime_variable_max_standby_archive_delay_milliseconds
pg_runtime_variable_max_standby_streaming_delay_milliseconds
```
which are replaced with
```
pg_settings_max_standby_archive_delay_seconds
pg_settings_max_standby_streaming_delay_seconds
```
Adds approximately 195 new metrics, when considered across all supported
PostgreSQL versions.
On a Debian + PostgreSQL 9.4 system I had a hard time getting the
exporter to work. It looks like I was running into some authentication
issues that weren't logged by sql.Open(), but by sql.DB.QueryRow().
This change extends the warning generated by the call to
checkMapVersions() to also print the error message generated by
sql.DB.QueryRow().
Similar to the node_exporter, this key is synthetic and used to create
a constant metric which records the version strings of PostgreSQL in its
labels.
Added metrics for locks per database per mode, pg_stat_activity, pg_stat_replication.
Updated README.md with possible solution for running as non-superuser.
This is based on the mysqld_exporter, but drastically changes how metrics are
discovered and enumerated since postgres already very closely follows the
Prometheus format.
