Export custom collectd PostgreSQL metrics to GCP Stackdriver Monitoring - stackdriver

Question

Background
I'm trying to export PostgreSQL replication delay by adding a custom <Query>
statement to my PostgreSQL config (original config from Stackdriver PostgreSQL
Plugin) in
stackdriver-agents collectd configuration
directory.
/opt/stackdriver/collectd/etc/postgresql.conf:
# This is the monitoring configuration for PostgreSQL.
# Make sure the statistics collector is enabled in your PostgreSQL configuration.
# NOTE: This configuration needs to be hand-edited in order to work.
# Look for DATABASE_NAME, STATS_USER, STATS_PASS, POSTGRESQL_HOST and POSTGRESQL_PORT to adjust your configuration file.
LoadPlugin postgresql
<Plugin "postgresql">
<Query replication_lag_seconds>
Statement "SELECT (CASE WHEN pg_last_xlog_receive_location() = pg_last_xlog_replay_location() THEN 0 ELSE EXTRACT (EPOCH FROM now() - pg_last_xact_replay_timestamp()) END) AS log_delay"
<Result>
Type "gauge"
ValuesFrom "log_delay"
</Result>
</Query>
# Each database needs a separate Database section.
# Replace DATABASE_NAME in the Database section with the name of the database.
<Database "THE_DATABASE">
# Host and port are only used for TCP/IP connections.
# Leaving them out indicates you wish to connect via domain sockets.
# When using non-standard PostgreSQL configurations, replace the below with
Host "localhost"
Port "5432"
User "THE_USER"
Password "hunter2"
Query backends
Query transactions
Query queries
Query table_states
Query disk_io
Query disk_usage
Query replication_lag_seconds # My custom query
</Database>
</Plugin>
The stackdriver-agent logs confirm that the plugin is loaded and that the plugin
is able to connect to the PostgreSQL server.
collectd[30418]: plugin_load: plugin "postgresql" successfully loaded.
collectd[13849]: Successfully connected to database THE_DATABASE (user THE_USER) at server localhost:5432 (server version: 9.4.12, protocol version: 3, pid: 13862)
By this time, I would expect to see my "log_delay" metric to show up in
Stackdriver monitoring when looking at metrics for the "Instance (GCE)"
resource. I can see that other PostgreSQL metrics have made it through, more
specifically:
I also can't seem to find any of the other default Query [...] metrics
inherited from the default PostgreSQL collectd configuration
referenced by Stackdriver PostgreSQL Plugin Documentation:
# [...]
LoadPlugin postgresql
<Plugin "postgresql">
# [...]
<Database "DATABASE_NAME">
# [...]
User "STATS_USER"
Password "STATS_PASS"
Query backends
Query transactions
Query queries
Query table_states
Query disk_io
Query disk_usage
</Database>
</Plugin>
Question
How do I get my collecd custom replication_lag_seconds metric to show up in Stackdriver Monitoring?
Do I need to configure Custom
Metrics in order to get
the metrics to show up in Stackdriver Monitoring?

Answer 1

The Stackdriver monitoring agent sends a set of curated metrics for each supported third-party application. That set cannot be extended by users -- anything that isn't a curated metric will be ignored by the API and must be sent via the custom metrics mechanism.