Re: BLOBs, MySQL, hex. Oh my

FROM : Ben Einstein
DATE : Thu May 08 03:05:47 2008

Well,

I know what's happening, so I don't think Shark or Instruments can 
help any. I just don't know WHY it happens.

This is the code i've been playing with (from Hayden Stainsby):

int            i;
        const char    *thumbnailHex;

        thumbnailHex = [thumbnailDataHex bytes];
        for (i = 0; i < strlen(thumbnailHex); i += 2)  {
            char    aByte, tChar[2];

            tChar[0] = thumbnailHex[i];
            tChar[1] = thumbnailHex[i+1];

            tChar[0] -= 0x30;
            if (tChar[0] >= 0x0a)
                tChar[0] -= 0x07;

            tChar[1] -= 0x30;
            if (tChar[1] >= 0x0a)
                tChar[1] -= 0x07;

            aByte = tChar[0] << 4;
            aByte = aByte | (tChar[1]);

            [thumbnailData appendBytes:&aByte length:1];
        }
        thumbnailImage = [[NSImage alloc] initWithData:thumbnailData];

I've actually done a few tests where this method loops for longer than 
90 seconds. On an NSImage object with the same number of bytes, it's 
somewhere in the 0.1 second range.

So very confused...

Ben


On May 7, 2008, at 8:21 PM, John Stiles wrote:

> Have you tried running Shark? That might give you some insight as to 
> what's going on.
>
> Ben Einstein wrote:

>> Hi All,
>>
>> I have an enterprise DB application that once used DO to move some 
>> files around (images and zip files, mostly). After some serious 
>> testing and lots of reading, I decided to move this to a few 
>> different BLOB fields in the database. Despite major warnings from 
>> people, I've found that images work great (specifically, NSData/
>> NSImage). I can notice a very minor speed drop a few milliseconds, 
>> but being able to drop DO and it's woes is completely worth it.
>>
>> Unfortunately, I didn't quite test the zip files, figuring it would 
>> be the same. I'm using Serge Cohen's MCPKit (aka SMySQL), which has 
>> a nifty little function to convert NSData to a MySQL-legal 
>> NSString. On the other end, someone on the Apple list posted a few 
>> lines of code to bump returned data into it's original NSData 
>> object. With the zip files (no larger then 600kb) that method takes 
>> 30 - 40 seconds to run. On an image of a similar size, it takes 0.1 
>> seconds on a slow day.
>>
>> Does anyone know why this would be? Is there an easy way to get 
>> around this? I suppose my understating of hex is lacking, but I 
>> always thought a hex string was a hex string was a hex string; 
>> length was all that mattered.
>>
>> Thanks,
>> Ben Einstein
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