Configuring EDB OTEL

The following configuration options are available with edb_otel.

Permissions

No permissions changes are required for edb_otel.

Prerequisites

Before using edb_otel to export metrics, you must set up an OpenTelemetry collector endpoint that edb_otel can communicate with. For detailed information on how to set up a quick test of the OpenTelemetry endpoint using Docker, see OTLP Exporter Example.

GUCs

The following GUC variables are available in edb_otel.

Configuring to use from an SQL interface

To use the edb_otel extension from a SQL interface, in postgresql.conf:

1. Set the parameter edb_otel.edb_otel_endpoint to point to the collector endpoint. For example:

edb_otel.edb_otel_endpoint='localhost:4317'

2. Add edb_otel to the shared_preload_libraries. For example:

shared_preload_libraries = '$libdir/dbms_pipe,$libdir/edb_gen,$libdir/dbms_aq,$libdir/edb_otel'

Configuring to use in C code

To use the edb_otel extension from your C code:

1. Ensure the edb_otel_ext.h file is in reach of your extension at build time. The file is placed in $prefix/include/server/extension/edb_otel/ when the edb_otel dev/devel package is installed. Your makefile must add pg_config --includedir-server to its include search paths so your extension can use it as:

#include "extension/edb_otel/edb_otel_ext.h"

This header contains the signature of the function that's used to send metrics to the OTEL endpoint.

2. When the edb_otel extension is loaded, it places a function pointer in the rendezvous variable identified by edb_otel_metric_func. So the next step is to get that function pointer:

edb_otel_metric_func_type * p_edb_otel_metric =
    (edb_otel_metric_func_type *) find_rendezvous_variable("edb_otel_metric_func");

You can store the function pointer in a session-long variable, but take care in case edb_otel gets loaded after the calling code.

Since the instrumented code must continue to work even when edb_otel isn't in use, if the function pointer returns NULL, no error should be raised, and the function must not be called.

For example, instrumenting pg_stat_statements to send the number of plans can look similar to this:

if (*p_edb_otel_metric) {
    char val[100] = {0};
    sprintf(val, "%ld", e->counters.calls[PGSS_PLAN]);
    (*p_edb_otel_metric)("pg_stat_statements",
                         "plans",
                         EDB_OTEL_GAUGE,
                         val,
                         labels);
}

The edb_otel_metric function has the following parameters.

For a detailed example of this C API usage, where pg_stat_statements was instrumented to send all metrics through OTEL, see this example.