iPhone-遍历SQLite数据库花费的时间太长

Question

Hi folks hope you can help. I'm attempting to create an anagram checker for an iPhone application. What I want to do is to be able to take a long string of maximum 81 letters and then check this against a word list to find all possible permutations of any length.

I've figured out how to do this on the simulator, but when I run this on the iPhone it is extremely slow, taking around 90 seconds to loop through the entire db (about 110000 rows). I checked Instruments and it doesn't show any memory leaks. However when I use Object Allocations it is clear that running the query creates a massive allocation for CFString that drains everything else. This immediately runs up 3.09 MB under the overall bytes column. (In the code below, I've stripped out all of the anagram checking code as I wanted to identify what was causing the problem. So all this does at present is loop through the db without any output).

//create query
    NSString *querySQL2 = @"SELECT name FROM table ";

    sqlite3_stmt *statement2;
    const char *query_stmt2 = [querySQL2 UTF8String];



    sqlite3_prepare_v2(contactDB, query_stmt2, -1, &statement2, NULL);


    //loop through all rows of database
    while (sqlite3_step(statement2) == SQLITE_ROW)
    {
        NSString *laststring = [[NSString alloc] initWithUTF8String:
                          (const char *) sqlite3_column_text(statement2, 0)];



        [laststring release];
        }


    sqlite3_finalize(statement2);
   sqlite3_close(contactDB);

    }

It seems obvious to me that the creation of 'laststring' below is what is sucking up all the memory. So why is it that when I put [laststring release]; at the end of the while loop it appears to have no effect? I've run this code with and without releasing and the same quantity of memory is used up. I've also tried wrapping an autorelease around it and this also had no effect.

I've read several other queries on looping through SQLite. Some of them suggested indexing but I'm not sure this will save me significant amounts of time with this problem. Also if I am searching all possible permutations from a large string of 81 letters, I'm guessing that at least 50% of the word list will need to be checked through anyway.

Any suggestions on how to keep CFString down? Many thanks Dave

Answer 1

Why do you alloc the NSString inside the while() loop?

while(sqlite3_step(compiledStatement) == SQLITE_ROW) 
      {
      NSString *laststring = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement2, 0)];    
      // do something with laststring
      }

would suffice wouldn't it?