Question

I spent hours trying to fix that but I’ve just given up; I have no idea what’s wrong.

In my app, I do nested SQL operations to set all my objects correctly. For some reason, sometimes the sqlite3 objects do not get release properly, causing the memory to go up the roof. I understand it is a problem with using correctly sql3_close and sql3_finalize. However, as you will see, I think I have used them correctly.

Here is the source of the problem:

- (NSArray *) getAllSessions {
    if (sqlite3_open(dbPath, &db) == SQLITE_OK) { 
        if (sqlite3_prepare_v2(db, query_stmt, -1, &statement, NULL) == SQLITE_OK) {
            while (sqlite3_step(statement) == SQLITE_ROW) {

                //I found out that doing something like that
                //toAdd.in_loc = [self getIndoorLocationWithId:[NSNumber numberWithInt:(int)sqlite3_column_int(statement, 6)]];
                //messes the memory up all the time
                //but doing that works OK:
                NSNumber *_id = [[NSNumber alloc]  initWithInt:(int) sqlite3_column_int(statement, 5)];
                toAdd.out_loc = [self getOutdoorLocationWithId:_id];
                [_id release];

                //So I did the same with the second one, but this one messes memory up:
                NSNumber *id2 = [[NSNumber alloc] initWithInt:(int)sqlite3_column_int(statement, 6)];
                toAdd.in_loc = [self getIndoorLocationWithId:id2];
                [id2 release];
            }
            sqlite3_finalize(statement);
        }
        sqlite3_close(db);
    } 
}

So here is the one that messes memory up:

- (IndoorLocation *) getIndoorLocationWithId:(NSNumber *) locId {
    if (sqlite3_open([databasePath UTF8String], &db) == SQLITE_OK) { 
        if (sqlite3_prepare_v2(db, query_stmt, -1, &statement, NULL) == SQLITE_OK) {
            while (sqlite3_step(statement) == SQLITE_ROW) {  
                //if I comment the thing below it works
                NSNumber *_id = [[NSNumber alloc]  initWithInt:(int) sqlite3_column_int(statement, 5)];
                toReturn.outLoc = [self getOutdoorLocationWithId:_id];
                [_id release];

            }
            sqlite3_finalize(statement);
        }
        sqlite3_close(db);
    }
}

So in the one that messes memory up, I use exactly the same function as the first time (getOutdoorLocationwithId), in the same way but it doesn’t work, sqlite3 objects don’t get released properly.

I hope you understand my problem, this is driving me nuts!

Answer 1

In a single user app like this, there’s no need to continually open and close. This is not like a server based app where you have connection pooling with multiple users where holding the connection can defeat the pool and hurt scalability. In a phone app open it and hold it open. close it when you’re done. At a minimum, do that within a recursive call.

To make it worse, you’re opening and closing within recursive calls – just leave it open.

Also:

• You’re not checking the return codes of finalize
• You’re not checking the return codes of close.
• You’re preparing (compiling) the statments but you’re not saving them off – call reset on the saved statement and execute it again.

Consider using FMDB – it’s a good wrapper.

BTW, here’s a richer and more durable close but don’t use it on every call. Close it when you’re ending or your app is going into the background … This is mine which is similar to what fmdb does.

- (void)close
{
    if (_sqlite3)
    {
        ENInfo(@"closing");
        [self clearStatementCache];

        int rc = sqlite3_close(_sqlite3);
        ENDebug(@"close rc=%d", rc);

        if (rc == SQLITE_BUSY) 
        { 
            ENError(@"SQLITE_BUSY: not all statements cleanly finalized");

            sqlite3_stmt *stmt; 
            while ((stmt = sqlite3_next_stmt(_sqlite3, 0x00)) != 0) 
            {
                ENDebug(@"finalizing stmt");
                sqlite3_finalize(stmt); 
            }

            rc = sqlite3_close(_sqlite3);
        }

        if (rc != SQLITE_OK)
        {
            ENError(@"close not OK.  rc=%d", rc);
        }

        _sqlite3 = NULL;
    }
}