Re: reading (parsing) CSV (or Excel) data
Re: reading (parsing) CSV (or Excel) data
- Subject: Re: reading (parsing) CSV (or Excel) data
- From: "Adam R. Maxwell" <email@hidden>
- Date: Fri, 02 Oct 2009 06:49:28 -0700
On Oct 2, 2009, at 6:10 AM, I. Savant wrote:
On Oct 2, 2009, at 7:42 AM, Mike Abdullah wrote:
While using this code in an experimental project I found the app
was routinely using 500+ MB of RAM. When measured with Instruments
I realised that every time you use a character set for string
scanning, Foundation internally copies it, presumably to ensure it
has an immutable object to work with. As a result, potentially
thousands of copies are being created, resulting in either:
A) Outrunning the garbage collector
B) Spending far more time allocating and deallocating character
sets than doing the actual scanning
Easiest solution is just to make a single copy yourself early on.
Also the docs for NSMutableCharacterSet do point out that it's
inefficient but don't really offer any detail.
Very good to know, thanks, Mike. You might want to post a comment
on the macresearch.org page so Drew can adjust the example.
I've also run into major performance problems with -[NSScanner
scanCharactersFromSet:], which creates an inverted, autoreleased
character set each time it's called. This blows up autorelease pools
(and inverting character sets isn't fast either). Filed as rdar://problem/4652388.
My workaround for this is generally to invert the set myself and use
scanUpToCharactersFromSet:, but that could be hurting this example as
well.
Do you happen to remember what percentage of difference you were
able to achieve? It's fine if not - it's not too difficult to set up
a test. :-)
In my case I was running out of address space and crashing, which is
pretty easy to detect :).
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