bookkeeper: don't flood logs if we have many channelmoves all at once.

Since we're synchronous, these only reach lightningd after we're done:
in the case of 1.6M channelmoves, that can give it major heartburn.

In practice, this reduces the first bkpr command on a fresh upgrade
from 349 to 235 seconds (but this was before other improvements we did
this release).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: Plugins: `bookkeeper` reduced logging for large imports to increase speed.

Author: rustyrussell

plugins/bkpr/bookkeeper.c

@@ -87,7 +87,8 @@ static void
 parse_and_log_channel_move(struct command *cmd,
 			   const char *buf,
 			   const jsmntok_t *channelmove,
-			   struct refresh_info *rinfo);
+			   struct refresh_info *rinfo,
+			   bool log);
 
 static struct command_result *datastore_done(struct command *cmd,
 					     const char *method,
@@ -120,8 +121,15 @@ static struct command_result *listchannelmoves_done(struct command *cmd,
 	be64 be_index;
 
 	moves = json_get_member(buf, result, "channelmoves");
+	if (moves->size > 2) {
+		plugin_log(cmd->plugin, LOG_DBG,
+			   "%u channelmoves, only logging first and last",
+			   moves->size);
+	}
+
 	json_for_each_arr(i, t, moves)
-		parse_and_log_channel_move(cmd, buf, t, rinfo);
+		parse_and_log_channel_move(cmd, buf, t, rinfo,
+					   i == 0 || i == moves->size - 1);
 
 	be_index = cpu_to_be64(bkpr->channelmoves_index);
 	jsonrpc_set_datastore_binary(cmd, "bookkeeper/channelmoves_index",
@@ -1277,7 +1285,8 @@ static void
 parse_and_log_channel_move(struct command *cmd,
 			   const char *buf,
 			   const jsmntok_t *channelmove,
-			   struct refresh_info *rinfo)
+			   struct refresh_info *rinfo,
+			   bool log)
 {
 	struct channel_event *e = tal(cmd, struct channel_event);
 	struct account *acct;
@@ -1324,11 +1333,12 @@ parse_and_log_channel_move(struct command *cmd,
 		err = tal_free(err);
 	}
 
-	plugin_log(cmd->plugin, LOG_DBG, "coin_move 2 (%s) %s -%s %s %"PRIu64,
-		   e->tag,
-		   fmt_amount_msat(tmpctx, e->credit),
-		   fmt_amount_msat(tmpctx, e->debit),
-		   CHANNEL_MOVE, e->timestamp);
+	if (log)
+		plugin_log(cmd->plugin, LOG_DBG, "coin_move 2 (%s) %s -%s %s %"PRIu64,
+			   e->tag,
+			   fmt_amount_msat(tmpctx, e->credit),
+			   fmt_amount_msat(tmpctx, e->debit),
+			   CHANNEL_MOVE, e->timestamp);
 
 	/* Go find the account for this event */
 	acct = find_account(bkpr, acct_name);