Log shard map and protocol version updates explicitly

We don't need to know for every backend when they connect to pageserver, we
only need to know when the connection fails. So, reduce all LOG lines in
connection start to DEBUG1.

Also do some stylistic conversions of existing log lines for improved filtering
on specific clauses.

pgxn/neon/libpagestore.c

@@ -49,7 +49,9 @@ char	   *neon_auth_token;
 int			readahead_buffer_size = 128;
 int			flush_every_n_requests = 8;
 
-int         neon_protocol_version = 2;
+int			neon_protocol_version = 2;
+static int	last_protocol_version = -1;	/* copy of n_p_v used to detect changes
+										 * to the parameter at runtime */
 
 static int	max_reconnect_attempts = 60;
 static int	stripe_size;
@@ -230,6 +232,14 @@ AssignPageserverConnstring(const char *newval, void *extra)
 		memcpy(&pagestore_shared->shard_map, &shard_map, sizeof(ShardMap));
 		pg_write_barrier();
 		pg_atomic_add_fetch_u64(&pagestore_shared->end_update_counter, 1);
+
+		neon_log(LOG, "Updated shard map: %d active shards",
+				 shard_map.num_shards);
+		for (int i = 0; i < shard_map.num_shards; i++)
+		{
+			neon_shard_log(i, LOG, "New connection string: \"%s\"",
+						   shard_map.connstring[i]);
+		}
 	}
 	else
 	{
@@ -616,6 +626,9 @@ pageserver_connect(shardno_t shard_no, int elevel)
 		/* fallthrough */
 	}
 	case PS_Connected:
+	{
+		int			ll;
+
 		/*
 		 * We successfully connected. Future connections to this PageServer
 		 * will do fast retries again, with exponential backoff.
@@ -623,8 +636,18 @@ pageserver_connect(shardno_t shard_no, int elevel)
 		shard->delay_us = MIN_RECONNECT_INTERVAL_USEC;
 
 		neon_shard_log(shard_no, DEBUG5, "Connection state: Connected");
-		neon_shard_log(shard_no, LOG, "libpagestore: connected to '%s' with protocol version %d", connstr, neon_protocol_version);
+		if (last_protocol_version != neon_protocol_version)
+		{
+			ll = LOG;
+			last_protocol_version = neon_protocol_version;
+		}
+		else
+		{
+			ll = DEBUG1;
+		}
+		neon_shard_log(shard_no, ll, "libpagestore: connected to '%s' with protocol version %d", connstr, neon_protocol_version);
 		return true;
+	}
 	default:
 		neon_shard_log(shard_no, ERROR, "libpagestore: invalid connection state %d", shard->state);
 	}
@@ -725,7 +748,7 @@ pageserver_send(shardno_t shard_no, NeonRequest *request)
 	/* If the connection was lost for some reason, reconnect */
 	if (shard->state == PS_Connected && PQstatus(shard->conn) == CONNECTION_BAD)
 	{
-		neon_shard_log(shard_no, LOG, "pageserver_send disconnect bad connection");
+		neon_shard_log(shard_no, LOG, "pageserver_send disconnect: bad connection");
 		pageserver_disconnect(shard_no);
 		pageserver_conn = NULL;
 	}
@@ -826,7 +849,7 @@ pageserver_receive(shardno_t shard_no)
 		}
 		PG_CATCH();
 		{
-			neon_shard_log(shard_no, LOG, "pageserver_receive: disconnect due malformatted response");
+			neon_shard_log(shard_no, LOG, "pageserver_receive disconnect: malformatted response");
 			pageserver_disconnect(shard_no);
 			PG_RE_THROW();
 		}
@@ -879,7 +902,7 @@ pageserver_flush(shardno_t shard_no)
 			char	   *msg = pchomp(PQerrorMessage(pageserver_conn));
 
 			pageserver_disconnect(shard_no);
-			neon_shard_log(shard_no, LOG, "pageserver_flush disconnect because failed to flush page requests: %s", msg);
+			neon_shard_log(shard_no, LOG, "pageserver_flush disconnect: failed to flush page requests: %s", msg);
 			pfree(msg);
 			return false;
 		}
@@ -1055,6 +1078,14 @@ pg_init_libpagestore(void)
 							0,	/* no flags required */
 							NULL, NULL, NULL);
 
+	/*
+	 * Store last seen protocol version as initialization, so we can log
+	 * differences once we see them appear.
+	 */
+	last_protocol_version = neon_protocol_version;
+	neon_log(LOG, "Initializing libpagestore with protocol version %d",
+			 neon_protocol_version);
+
 	relsize_hash_init();
 
 	if (page_server != NULL)
@@ -1069,7 +1100,7 @@ pg_init_libpagestore(void)
 	 */
 	neon_auth_token = getenv("NEON_AUTH_TOKEN");
 	if (neon_auth_token)
-		neon_log(LOG, "using storage auth token from NEON_AUTH_TOKEN environment variable");
+		neon_log(DEBUG1, "using storage auth token from NEON_AUTH_TOKEN environment variable");
 
 	if (page_server_connstring && page_server_connstring[0])
 	{