Re: Reading in dictionary from txt file: options for speed
Re: Reading in dictionary from txt file: options for speed
- Subject: Re: Reading in dictionary from txt file: options for speed
- From: WT <email@hidden>
- Date: Thu, 16 Apr 2009 04:01:22 +0200
Hi Marcel,
that's quite impressive. On the simulator on my machine, it took 0.007
seconds, consistently. Learned something new with your message. Thanks!
Wagner
On Apr 16, 2009, at 12:35 AM, Marcel Weiher wrote:
I would do the following:
1. map the file into memory using -[NSData
dataWithContentsOfMappedFile:] (or mmap() if you really want to)
2. Do not convert to individual objects for the words
3. get the pointer to the raw bytes
4. search using a little bit of plain old C (assuming you're OK with
encodings)
Memory mapping will be essentially instantaneous, with the I/O
performed on-demand when its actually needed (or you can pre-heat
the data, for example in a background thread). More importantly,
you will be doing good things for memory consumption, because the
mapped memory can be released to the OS without having to kill your
app in low-memory situations (without paging it out on Mac OS X, but
the iPhone doesn't page memory out).
I added an implementation of this approach to the testing program
provided by Wagner (thanks!) and it loads + counts the words in
0.084 seconds on the device. That's anywhere from around 50 - 100
times faster than the other methods implemented in DictTest (plist /
xml / txt ). On the simulator, it runs in 0.043 seconds, so around
30-40 times faster than the other methods.
Download can be found here:
http://www.metaobject.com/downloads/Objective-C/DictTest.tgz
You mentioned that you were OK with search performance, so I won't
go into that.
Cheers,
Marcel
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