Allow changing otel endpoint setting without restart

README.md

@@ -155,3 +155,5 @@ pg_tracing.otel_naptime = 2000
 ```
 
 If an otel endpoint is defined, a background worker will be started and will send spans every $naptime using the OTLP HTTP/JSON protocol.
+The endpoint can be changed while the server is running, but if it was not set when the server was started, changing it to non-empty value
+requires a restart.

src/pg_tracing.c

@@ -123,13 +123,13 @@ static int	pg_tracing_buffer_mode = PG_TRACING_KEEP_ON_FULL;	/* behaviour on ful
 																 * buffer */
 static char *pg_tracing_filter_query_ids = NULL;	/* only sample query
 													 * matching query ids */
-static char *pg_tracing_otel_endpoint = NULL;	/* Otel collector to send
+char	   *pg_tracing_otel_endpoint = NULL;	/* Otel collector to send
 												 * spans to */
 char	   *pg_tracing_otel_service_name = NULL;	/* Service name set in
 													 * otel traces */
-static int	pg_tracing_otel_naptime;	/* Delay between upload of spans to
+int			pg_tracing_otel_naptime;	/* Delay between upload of spans to
 										 * otel collector */
-static int	pg_tracing_otel_connect_timeout_ms; /* Connect timeout to the otel
+int			pg_tracing_otel_connect_timeout_ms; /* Connect timeout to the otel
 												 * collector */
 static char *guc_tracecontext_str = NULL;	/* Trace context string propagated
 											 * through GUC variable */
@@ -448,7 +448,7 @@ _PG_init(void)
 							10000,
 							1000,
 							500000,
-							PGC_POSTMASTER,
+							PGC_SIGHUP,
 							0,
 							NULL,
 							NULL,
@@ -461,29 +461,29 @@ _PG_init(void)
 							1000,
 							100,
 							600000,
-							PGC_POSTMASTER,
+							PGC_SIGHUP,
 							0,
 							NULL,
-							NULL,
+							&otel_config_int_assign_hook,
 							NULL);
 
 	DefineCustomStringVariable("pg_tracing.otel_endpoint",
 							   "Otel endpoint to send spans.",
 							   "If unset, no background worker to export to otel is created.",
 							   &pg_tracing_otel_endpoint,
 							   NULL,
-							   PGC_POSTMASTER,
+							   PGC_SIGHUP,
 							   0,
 							   NULL,
-							   NULL,
+							   &otel_config_string_assign_hook,
 							   NULL);
 
 	DefineCustomStringVariable("pg_tracing.otel_service_name",
 							   "Service Name to set in traces sent to otel.",
 							   NULL,
 							   &pg_tracing_otel_service_name,
 							   "PostgreSQL_Server",
-							   PGC_POSTMASTER,
+							   PGC_SIGHUP,
 							   0,
 							   NULL,
 							   NULL,
@@ -536,8 +536,7 @@ _PG_init(void)
 	if (pg_tracing_otel_endpoint != NULL)
 	{
 		elog(INFO, "Starting otel exporter worker on endpoint %s", pg_tracing_otel_endpoint);
-		pg_tracing_start_worker(pg_tracing_otel_endpoint, pg_tracing_otel_naptime,
-								pg_tracing_otel_connect_timeout_ms);
+		pg_tracing_start_worker();
 	}
 }
 

src/pg_tracing.h

@@ -426,6 +426,9 @@ extern pgTracingSpans * shared_spans;
 extern char *shared_str;
 extern int	nested_level;
 extern char *pg_tracing_otel_service_name;
+extern char *pg_tracing_otel_endpoint;
+extern int	pg_tracing_otel_naptime;
+extern int	pg_tracing_otel_connect_timeout_ms;
 
 extern void
 			store_span(const Span * span);
@@ -464,6 +467,12 @@ extern Size
 
 /* pg_tracing_otel.c */
 extern void
-			pg_tracing_start_worker(const char *endpoint, int naptime, int connect_timeout_ms);
+			pg_tracing_start_worker(void);
+
+extern void
+			otel_config_int_assign_hook(int newval, void *extra);
+
+extern void
+			otel_config_string_assign_hook(const char *newval, void *extra);
 
 #endif

src/pg_tracing_otel.c

@@ -13,6 +13,7 @@
 #include "pg_tracing.h"
 #include "postmaster/bgworker.h"
 #include "postmaster/interrupt.h"
+#include "utils/guc.h"
 #include "utils/memutils.h"
 #include "storage/latch.h"
 #include "storage/procsignal.h"
@@ -28,10 +29,7 @@ typedef struct OtelContext
 	pgTracingSpans *spans;		/* A copy of spans to send */
 	char	   *spans_str;		/* A copy of span text */
 
-	const char *endpoint;		/* Target otel collector */
-	int			naptime;		/* Duration between upload ot spans to the
-								 * otel collector */
-	int			connect_timeout_ms; /* Connection timeout in ms */
+	bool		config_changed;
 }			OtelContext;
 
 /* State and configuration of the otel exporter */
@@ -106,8 +104,13 @@ send_json_trace(OtelContext * octx, const char *json_span)
 			return CURLE_FAILED_INIT;
 		}
 		curl_easy_setopt(octx->curl, CURLOPT_HTTPHEADER, octx->headers);
-		curl_easy_setopt(octx->curl, CURLOPT_URL, octx->endpoint);
-		curl_easy_setopt(octx->curl, CURLOPT_CONNECTTIMEOUT_MS, octx->connect_timeout_ms);
+		octx->config_changed = true;
+	}
+	if (octx->config_changed)
+	{
+		curl_easy_setopt(octx->curl, CURLOPT_URL, pg_tracing_otel_endpoint);
+		curl_easy_setopt(octx->curl, CURLOPT_CONNECTTIMEOUT_MS, pg_tracing_otel_connect_timeout_ms);
+		octx->config_changed = false;
 	}
 	curl_easy_setopt(octx->curl, CURLOPT_POSTFIELDS, json_span);
 	curl_easy_setopt(octx->curl, CURLOPT_POSTFIELDSIZE, (long) strlen(json_span));
@@ -137,7 +140,7 @@ send_json_to_otel_collector(OtelContext * octx, JsonContext * json_ctx)
 {
 	CURLcode	ret;
 
-	elog(INFO, "Sending %d spans to %s", json_ctx->num_spans, octx->endpoint);
+	elog(INFO, "Sending %d spans to %s", json_ctx->num_spans, pg_tracing_otel_endpoint);
 	ret = send_json_trace(octx, json_ctx->str->data);
 	if (ret == CURLE_OK)
 	{
@@ -222,7 +225,7 @@ send_spans_to_otel_collector(OtelContext * octx, JsonContext * json_ctx)
  * Register otel exporter background worker
  */
 void
-pg_tracing_start_worker(const char *endpoint, int naptime, int connect_timeout_ms)
+pg_tracing_start_worker(void)
 {
 	BackgroundWorker worker;
 	BackgroundWorkerHandle *handle;
@@ -237,13 +240,6 @@ pg_tracing_start_worker(const char *endpoint, int naptime, int connect_timeout_m
 	strcpy(worker.bgw_name, "pg_tracing otel exporter");
 	strcpy(worker.bgw_type, "pg_tracing otel exporter");
 
-	/* Initialize the otel context struct */
-	otel_context.headers = NULL;
-	otel_context.curl = NULL;
-	otel_context.endpoint = endpoint;
-	otel_context.naptime = naptime;
-	otel_context.connect_timeout_ms = connect_timeout_ms;
-
 	if (process_shared_preload_libraries_in_progress)
 	{
 		RegisterBackgroundWorker(&worker);
@@ -277,6 +273,10 @@ pg_tracing_otel_exporter(Datum main_arg)
 
 	json_ctx.str = NULL;
 
+	/* Initialize the otel context struct */
+	otel_context.headers = NULL;
+	otel_context.curl = NULL;
+
 	/* Establish signal handlers; once that's done, unblock signals. */
 	pqsignal(SIGTERM, SignalHandlerForShutdownRequest);
 	pqsignal(SIGHUP, SignalHandlerForConfigReload);
@@ -321,12 +321,26 @@ pg_tracing_otel_exporter(Datum main_arg)
 	while (!ShutdownRequestPending)
 	{
 		int			rc;
+		int			wakeEvents;
 
 		/* Clean the latch and wait for the next event */
 		ResetLatch(MyLatch);
-		rc = WaitLatch(MyLatch,
-					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
-					   otel_context.naptime,
+
+		if (ConfigReloadPending)
+		{
+			ConfigReloadPending = false;
+			ProcessConfigFile(PGC_SIGHUP);
+		}
+
+		/*
+		 * If disabled by setting endpoint to empty, sleep until woken up by
+		 * another configuration change.
+		 */
+		wakeEvents = WL_LATCH_SET | WL_EXIT_ON_PM_DEATH;
+		if (pg_tracing_otel_endpoint != NULL && pg_tracing_otel_endpoint[0] != '\0')
+			wakeEvents |= WL_TIMEOUT;
+
+		rc = WaitLatch(MyLatch, wakeEvents, pg_tracing_otel_naptime,
 					   PG_WAIT_EXTENSION);
 
 		/* Send spans if we have any */
@@ -344,3 +358,20 @@ pg_tracing_otel_exporter(Datum main_arg)
 	}
 	curl_global_cleanup();
 }
+
+/*
+ * Assign hooks to notice changes to GUCs that need to be also set on the Curl
+ * handle. (We don't dare to make the changes to the Curl handle here directly,
+ * in case there's an error.)
+ */
+void
+otel_config_int_assign_hook(int newval, void *extra)
+{
+	otel_context.config_changed = true;
+}
+
+void
+otel_config_string_assign_hook(const char *newval, void *extra)
+{
+	otel_context.config_changed = true;
+}