SQLite is so awesome

[chriscalef]

Sorry, but I just had to drop in and share my amazement with sqlite for a second. I've been using it for years, but have only just now taken the time to seriously optimize it. (My old methods were becoming unbearably slow when updating MegaMotion scenes involving a couple of hundred characters.) I could go on at length, but it really boils down to two things: prepared statements, and memory databases.

The second one is obvious, but I hadn't known sqlite could do that, or that it would be so easy. All you have to do is use ":memory:" as the name of your database file, and it creates the database in RAM. Then a few lines of sample code from sqlite.org gets you loading and saving from the regular disk database file, and suddenly all of your interactions are internal instead of doing a separate disk access for every SQL statement. More on this here.

Prepared statements are compiled SQL queries, of a form looking like "... WHERE id=?;", so that you can compile the query once and run it many times in a loop, changing the variables out every time without having to reinterpret the SQL every time. More on this here.

Since my noticeable access lag time dropped to effectively zero when I went to the cached database, I'm not sure how much the prepared statements are actually helping me, but they're definitely a good thing to know about.

Here is my version of sqlite.org's loadOrSaveDb function, modified to work with the T3D SQLiteObject resource.

 

/*
** This function is used to load the contents of a database file on disk
** into the "main" database of open database connection pInMemory, or
** to save the current contents of the database opened by pInMemory into
** a database file on disk. pInMemory is probably an in-memory database,
** but this function will also work fine if it is not.
**
** Parameter zFilename points to a nul-terminated string containing the
** name of the database file on disk to load from or save to. If parameter
** isSave is non-zero, then the contents of the file zFilename are
** overwritten with the contents of the database opened by pInMemory. If
** parameter isSave is zero, then the contents of the database opened by
** pInMemory are replaced by data loaded from the file zFilename.
**
** If the operation is successful, SQLITE_OK is returned. Otherwise, if
** an error occurs, an SQLite error code is returned.
*/
int SQLiteObject::loadOrSaveDb(const char *zFilename, bool isSave) {
int rc;                   /* Function return code */
sqlite3 *pFile;           /* Database connection opened on zFilename */
sqlite3_backup *pBackup;  /* Backup object used to copy data */
sqlite3 *pTo;             /* Database to copy to (pFile or pInMemory) */
sqlite3 *pFrom;           /* Database to copy from (pFile or pInMemory) */

						  /* Open the database file identified by zFilename. Exit early if this fails
						  ** for any reason. */

Con::printf("calling loadOrSaveDb, isSave = %d", isSave);

if (isSave == false)
{//If we're loading, have to create the memory database.
	if (!(SQLITE_OK == sqlite3_open(":memory:", &m_pDatabase)))
	{
		Con::printf("Unable to open a memory database!");
		return 0;
	}
}
rc = sqlite3_open(zFilename, &pFile);
if (rc == SQLITE_OK) {

	/* If this is a 'load' operation (isSave==0), then data is copied
	** from the database file just opened to database pInMemory.
	** Otherwise, if this is a 'save' operation (isSave==1), then data
	** is copied from pInMemory to pFile.  Set the variables pFrom and
	** pTo accordingly. */
	pFrom = (isSave ? m_pDatabase : pFile);
	pTo = (isSave ? pFile : m_pDatabase);

	/* Set up the backup procedure to copy from the "main" database of
	** connection pFile to the main database of connection pInMemory.
	** If something goes wrong, pBackup will be set to NULL and an error
	** code and message left in connection pTo.
	**
	** If the backup object is successfully created, call backup_step()
	** to copy data from pFile to pInMemory. Then call backup_finish()
	** to release resources associated with the pBackup object.  If an
	** error occurred, then an error code and message will be left in
	** connection pTo. If no error occurred, then the error code belonging
	** to pTo is set to SQLITE_OK.
	*/
	pBackup = sqlite3_backup_init(pTo, "main", pFrom, "main");
	if (pBackup) {
		(void)sqlite3_backup_step(pBackup, -1);
		(void)sqlite3_backup_finish(pBackup);
	}
	rc = sqlite3_errcode(pTo);
}

/* Close the database connection opened on database file zFilename
** and return the result of this function. */
(void)sqlite3_close(pFile);

//if (isSave ==  true)  // Actually, cancel this, I'm sure it will happen automatically and if we don't do it here, we can also use
//{                     // this function for periodic saves, such as after saving mission.
//	sqlite3_close(m_pDatabase);
//}

Con::printf("finished loadOrSaveDb, rc = %d", rc);

if (rc == 0)
	return true;
else
	return false;
}

[JeffR]

I had no idea sqlite could do that stuff. That's pretty sweet, actually, thanks for the info! :)

[chriscalef]

My pleasure, @JeffR!

Here's a link to my current version of SQLiteObject, and the latest sqlite3 files. Just a warning, you have to compile sqlite3.c as C code, not C++, if you're using VS 2015.