Considered exposing the ability to set Sqlite DB journal mode to WAL?

[antoinemacia]

We're looking to allow concurrent reads (non blocking) during mapping on the iOS app - wondering if Write Ahead Logging wasnt exposed for a reason (maybe it wasnt released then..

Currently doing PRAGMA journal_mode=WAL; but would be happy to extend the params and make a PR if that's of interest!

[matlabbe]

Yeah, we could add this mode, probably here:

rtabmap/corelib/src/DBDriverSqlite3.cpp

Lines 110 to 135 in 1def668

	void DBDriverSqlite3::setJournalMode(int journalMode)
	{
	if(journalMode >= 0 && journalMode < 5)
	{
	_journalMode = journalMode;
	if(this->isConnected())
	{
	switch(_journalMode)
	{
	case 4:
	this->executeNoResultQuery("PRAGMA journal_mode = OFF;");
	break;
	case 3:
	this->executeNoResultQuery("PRAGMA journal_mode = MEMORY;");
	break;
	case 2:
	this->executeNoResultQuery("PRAGMA journal_mode = PERSIST;");
	break;
	case 1:
	this->executeNoResultQuery("PRAGMA journal_mode = TRUNCATE;");
	break;
	case 0:
	default:
	this->executeNoResultQuery("PRAGMA journal_mode = DELETE;");
	break;
	}

Because parameter DbSqlite3/JournalMode = "3" [0=DELETE, 1=TRUNCATE, 2=PERSIST, 3=MEMORY, 4=OFF (see sqlite3 doc : "PRAGMA journal_mode")] exists and to be backward compatible, you may set 5=WAL. WAL was introduced in 2010, and based on "blame", that code was written prior the project migration to github (before 2011) so it could have been added before 2010 (original project started in January 2009)!

[antoinemacia]

Great, thought that was the case! Ill put something together