Add connection establishment duration logging

Add log_connections option 'setup_durations' which logs durations of
several key parts of connection establishment and backend setup.

For an incoming connection, starting from when the postmaster gets a
socket from accept() and ending when the forked child backend is first
ready for query, there are multiple steps that could each take longer
than expected due to external factors. This logging provides visibility
into authentication and fork duration as well as the end-to-end
connection establishment and backend initialization time.

To make this portable, the timings captured in the postmaster (socket
creation time, fork initiation time) are passed through the
BackendStartupData.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Fujii Masao <masao.fujii@oss.nttdata.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Reviewed-by: Guillaume Lelarge <guillaume.lelarge@dalibo.com>
Discussion: https://postgr.es/m/flat/CAAKRu_b_smAHK0ZjrnL5GRxnAVWujEXQWpLXYzGbmpcZd3nLYw%40mail.gmail.com

2 files changed, 44 insertions, 0 deletions

diff --git a/src/backend/tcop/backend_startup.c b/src/backend/tcop/backend_startup.c
index 962b6e60002..27c0b3c2b04 100644
--- a/src/backend/tcop/backend_startup.c
+++ b/src/backend/tcop/backend_startup.c
@@ -46,6 +46,16 @@ bool		Trace_connection_negotiation = false;
 uint32		log_connections = 0;
 char	   *log_connections_string = NULL;
 
+/* Other globals */
+
+/*
+ * ConnectionTiming stores timestamps of various points in connection
+ * establishment and setup.
+ * ready_for_use is initialized to a special value here so we can check if
+ * we've already set it before doing so in PostgresMain().
+ */
+ConnectionTiming conn_timing = {.ready_for_use = TIMESTAMP_MINUS_INFINITY};
+
 static void BackendInitialize(ClientSocket *client_sock, CAC_state cac);
 static int	ProcessSSLStartup(Port *port);
 static int	ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done);
@@ -1006,6 +1016,7 @@ validate_log_connections_options(List *elemlist, uint32 *flags)
 			{"receipt", LOG_CONNECTION_RECEIPT},
 			{"authentication", LOG_CONNECTION_AUTHENTICATION},
 			{"authorization", LOG_CONNECTION_AUTHORIZATION},
+			{"setup_durations", LOG_CONNECTION_SETUP_DURATIONS},
 			{"all", LOG_CONNECTION_ALL},
 		};
 
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 947ffb40421..55ab2da299b 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -66,6 +66,7 @@
 #include "storage/proc.h"
 #include "storage/procsignal.h"
 #include "storage/sinval.h"
+#include "tcop/backend_startup.h"
 #include "tcop/fastpath.h"
 #include "tcop/pquery.h"
 #include "tcop/tcopprot.h"
@@ -4607,6 +4608,38 @@ PostgresMain(const char *dbname, const char *username)
 			/* Report any recently-changed GUC options */
 			ReportChangedGUCOptions();
 
+			/*
+			 * The first time this backend is ready for query, log the
+			 * durations of the different components of connection
+			 * establishment and setup.
+			 */
+			if (conn_timing.ready_for_use == TIMESTAMP_MINUS_INFINITY &&
+				(log_connections & LOG_CONNECTION_SETUP_DURATIONS) &&
+				IsExternalConnectionBackend(MyBackendType))
+			{
+				uint64		total_duration,
+							fork_duration,
+							auth_duration;
+
+				conn_timing.ready_for_use = GetCurrentTimestamp();
+
+				total_duration =
+					TimestampDifferenceMicroseconds(conn_timing.socket_create,
+													conn_timing.ready_for_use);
+				fork_duration =
+					TimestampDifferenceMicroseconds(conn_timing.fork_start,
+													conn_timing.fork_end);
+				auth_duration =
+					TimestampDifferenceMicroseconds(conn_timing.auth_start,
+													conn_timing.auth_end);
+
+				ereport(LOG,
+						errmsg("connection ready: setup total=%.3f ms, fork=%.3f ms, authentication=%.3f ms",
+							   (double) total_duration / NS_PER_US,
+							   (double) fork_duration / NS_PER_US,
+							   (double) auth_duration / NS_PER_US));
+			}
+
 			ReadyForQuery(whereToSendOutput);
 			send_ready_for_query = false;
 		}