Re: BLOBs, MySQL, hex. Oh my
Re: BLOBs, MySQL, hex. Oh my
- Subject: Re: BLOBs, MySQL, hex. Oh my
- From: Ben Einstein <email@hidden>
- Date: Thu, 8 May 2008 12:11:46 -0400
Hi Serge,
It's really quite strange. MySQL does return an NSData object, but
there's a byte level problem. Again, I really don't know much about
this stuff but NSImage instances fail to be unarchived and zip files
can't be unpacked. From what I understand, MySQL is giving us back
hex. So I used your prepareBinaryData: method, but any time I got a
query back with that data, it was no good unless I ran Hayden's hex
conversion loop. My columns I'm writing to are of type LONGBLOB.
In regards to the Shark testing: I knew what loop was getting caught
up, I never, ever knew that Shark could get so specific as I've now
discovered. I shouldn't have dismissed that suggestion so soon. Most
of my experience with optimization is with Instuments (and their pre-
leopard counterparts), which can't get that specific (again, as far as
I know).
Ben
On May 8, 2008, at 9:01 AM, Serge Cohen wrote:
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Hello;
One thing I don't understand, is that in MCPKit, you're supposed to
"prepare" (that is hexcode) the BLOB when you perform the INSERT,
but when using a query and fetch a row, the column containing a BLOB
should already be returned as NSData... This NSData should represent
the exact binary replicate of the INSERTED NSData (before it was hex-
coded) ...
In other words, to my knowledge one would need to use the -
[MCPConnection prepareBinaryData:] method at the time of the insert,
but there should be NO need to any back conversion when getting the
result of a QUERY.
Is there something I'm missing here ? (unless you are indeed storing
your BLOB as a TEXT, in which case MySQL would store the hex-coded
text rather than the binary represented by it, and in which case it
would return the TEXT which you would have to UN-hexcode
yourself ... if this is the case, then the problem lies in the table
definition, you "just" have to make sure to declare the column as
BLOB rather than TEXT, right ?)
Serge.
Le 8 mai 08 à 02:16, Ben Einstein a écrit :
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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