Fix various player save issues (performance penalty on sql backends + bugs)

* PostgreSQL & SQLite3 doesn't setModified(false) on RemotePlayer, then player is saved on each server save call. This results in heavy useless writes.
* PostgreSQL & SQLite3 ack engine meta write whereas db commit hasn't been performed. If commit failed write has failed. We mustn't notify engine write is done.
* serializing player meta must not setModified(false) because it didn't ensure write has been done
* add RemotePlayer::on_successfull_save callback to do the flag update on a successful save

3 files changed, 6 insertions, 3 deletions

diff --git a/src/database/database-files.cpp b/src/database/database-files.cpp
index f42535348..b1c79c94a 100644
--- a/src/database/database-files.cpp
+++ b/src/database/database-files.cpp
@@ -105,7 +105,8 @@ void PlayerDatabaseFiles::savePlayer(RemotePlayer *player)
 	if (!fs::safeWriteToFile(path, ss.str())) {
 		infostream << "Failed to write " << path << std::endl;
 	}
-	player->setModified(false);
+
+	player->on_successful_save();
 }
 
 bool PlayerDatabaseFiles::removePlayer(const std::string &name)
diff --git a/src/database/database-postgresql.cpp b/src/database/database-postgresql.cpp
index eec838ef0..f5f8e3adf 100644
--- a/src/database/database-postgresql.cpp
+++ b/src/database/database-postgresql.cpp
@@ -527,8 +527,9 @@ void PlayerDatabasePostgreSQL::savePlayer(RemotePlayer *player)
 		};
 		execPrepared("save_player_metadata", 3, meta_values);
 	}
-	sao->getMeta().setModified(false);
 	endSave();
+
+	player->on_successful_save();
 }
 
 bool PlayerDatabasePostgreSQL::loadPlayer(RemotePlayer *player, PlayerSAO *sao)
diff --git a/src/database/database-sqlite3.cpp b/src/database/database-sqlite3.cpp
index aa156bbbd..7a79fb187 100644
--- a/src/database/database-sqlite3.cpp
+++ b/src/database/database-sqlite3.cpp
@@ -528,9 +528,10 @@ void PlayerDatabaseSQLite3::savePlayer(RemotePlayer *player)
 		sqlite3_vrfy(sqlite3_step(m_stmt_player_metadata_add), SQLITE_DONE);
 		sqlite3_reset(m_stmt_player_metadata_add);
 	}
-	sao->getMeta().setModified(false);
 
 	endSave();
+
+	player->on_successful_save();
 }
 
 bool PlayerDatabaseSQLite3::loadPlayer(RemotePlayer *player, PlayerSAO *sao)