Re: Reading from very large file
On 08.05.2010 20:55, Hakan wrote:
markspace wrote:
Hakan wrote:
I'd like to read only numbers from an extremely big file containing
both characters and digits. It turns out that a) reading each
character with a RandomAccessFile is too slow
I think a tightly scoped SSCCE is needed here. "Extremely big" and
"too slow" are such vague and relative terms that there's not really
much we can do if we don't know what sort of performance target we're
trying to hit.
SSCCE with the access times you are seeing, plus your desired
performance improvement, would be the best.
The text file has a size in the range of 13.7 MB. No matter what access
times I have on an individual read, it will take immense amounts of time
unless I find the smartest way to preprocess it and filter out all
non-digits. Thanks.
I have no idea what you want to do with those characters but what's
wrong with reading the file beginning to end with a fixed buffer size
and inspect the buffer? You won't get much more efficient than that
unless you have information about the file's format that can be exploited.
Btw, I don't even think that reading the whole file into memory and
process it there is completely ruled out yet. 28MB (which you need for
character data) is not much on modern operating systems. Granted, you
then should run your VM with more than the default memory sizes but
that's not really a big deal. But you should do that only if you really
have the need to jump back and forth in the file.
Cheers
robert
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