On 2012-11-08 at 11:36:37 +0100, Hans Hagen wrote:
On 11/8/2012 2:05 AM, Reinhard Kotucha wrote:
Thank you, Hans. Here it's faster than reading the file at once but still slower than reading 8k Blocks. It also consumes as much memory as reading the file at once (and memory consumption grows exponentially), but I could reduce memory consumption significantly replacing
return table.concat(data)
with
return data
table.concat() keeps the file twice in memory, once as a table and once as a string.
but if you want to compare the *all with blockwise loading you need to do the concat because otherwise you compare differen things; it's the concat that is costly (more than twice as much as the loading)
Yes, I removed it in order to confirm that it's responsible for the the memory consumption.
Yes, memory consumption is a problem on my machine at work. I'm running Linux in a virtual machine under 32-bit Windows. Windows can only use 3GB of memory and uses 800MB itself. Though I can assign more than 3GB to the VM, I suppose that I actually have less than 2.2GB and the rest is provided by a swap file. Furthermore, multi tasking/multi user systems can only work if no program assumes that it's the only one which is running.
ah, but using a vm is making comparison problematic because in many cases a vm's file handling can be faster than in bare metal (tex uses one core only but in a vm the second core kicks in for some management tasks)
Sorry, forgot to mention that I did all the comparisons on my 64-bit Linux box with 4GB RAM at home. Another problem at work is that I failed to compile xosview under CentOS. So I don't see when the system is swapping, which might happen frequently on the VM.
Speed is important in many cases. And I think that if you're writing a function you want to use in various scripts, it's worthwhile to evaluate the parameters carefully.
sure, i do lots of speed/efficiency tests
I know. However, I just installed Subversion and copiled the latest SVN version of LuaTeX on my Raspberry Pi. If you or anybody else is interested in benchmarks, just send me your test files.
The idea I had was to write a function which allows to read a text file efficiently. It should also be flexible and easy to use.
yes, but keep in mind that there are many parameters that influences it, like caching (an initial make format - fresh machine startup - can for instance take 5 times more time than a successive one and the same is true with this kind of tests)
When using the cache, I usually clear it first and then run the script several times. I also obey xosview in order to make sure that no other processes interfere. I think that an empty cache is what you have after a fresh startup. And the most important thing is that no web-browser is running when doing benchmarks.
In Lua it's convenient to read a file either line-by-line or at once. Both are not efficient. The first is extremely slow when lines are short and the latter consumes a lot of memory. And in many cases you don't even need the content of the whole file.
line based reading needs to parse lines; it's faster to read the whole file with "rb" and loop over lines with
for s in string.gmatch("(.-)\n") do
or something similar
Hmm, something similar is Taco's string.explode() function. It's much faster than regular expressions, so I prefer it. What I didn't consider yet is that the separator can only be either \r or \n and I have to know in advance which linebreaks are used. But I have some ideas how to solve the problem.
What I have so far is a function which reads a block and [the rest of] a line within an endless loop. Each chunk is split into lines. It takes two arguments, the file name and a function. For each chunk, the function is run on each line. Thus I'm able to filter the data and not everything has to be stored in memory.
------------------------------------------------ #! /usr/bin/env texlua --*- Lua -*-
function readfile (filename, fun) local lineno=1 fh=assert(io.open(filename, 'r')) while true do local line, rest = fh:read(2^13, '*line') if not line then break end if rest then line = line..rest end local tab = line:explode('\n') for i, v in ipairs(tab) do fun(v, lineno) lineno=lineno+1 end end fh:close() end
function process_line (line, n) print(n, line) end
readfile ('testfile', process_line)
you still store the exploded tab
------------------------------------------------
Memory consumption is either 8kB or the length of the longest line unless you store lines in a string or table. Almost no extra memory
you do store them as the explode splits a max 2^13 chunk into lines
Sure. But as far as I can see it doesn't hurt. The table is overwritten whenever a new chunk is processed. Thus, things don't accumulate. I don't know what happens when I overwrite a table. Maybe the new one allocates new memory and the old one is left to the garbage collector. But if this is the case, then the garbage collector does a pretty good job. The function is very fast and memory cunsumption isn't even visible in xosview. BTW, the f:read(BUFFER, '*line') concept can be less efficient if lines are extremely long...
is needed if you manipulate each line somehow and write the result to another file. The only files I encountered which are really large are CSV-like files which contain rows and columns of numbers, but the function process_line() allows me to select only the rows and columns I want to pass to pgfplots, for example.
at my end 2^24 is the most efficient (in time) block size
I found out that 2^13 is most efficient. But I suppose that the most important thing is that it's an integer multiple of a filesystem data block. Since Taco provided os.type() and os.name(), it's possible to to make the chunk size system dependent. But I fear that the actual hardware (SSD vs. magnetic disk) has a bigger impact than the OS.
it's not os dependent but filesystem dependent and often disk sector dependent
here's one that does not need the split
Well, it splits the file though: string.gmatch(buffer,"([^\n\r]-)(\r?\n)") I suppose that the most promising approach is to use regexps in order to determine the linebreak style, abort, and read the file again using Taco's function. Anyway, our discussion is obviously off-topic here. Hans, I'll inform you about the results by private mail. If anybody else is interested in the results, just drop me a line. Regards, Reinhard -- ---------------------------------------------------------------------------- Reinhard Kotucha Phone: +49-511-3373112 Marschnerstr. 25 D-30167 Hannover mailto:reinhard.kotucha@web.de ---------------------------------------------------------------------------- Microsoft isn't the answer. Microsoft is the question, and the answer is NO. ----------------------------------------------------------------------------