winapi - optimization of sequential i/o operations on large file sizes - 


compiler:  microsoft c++ 2005
hardware:  amd 64-bit (16 gb)


sequential, read-only access 18gb file committed following timing, file access, , file structure characteristics:

18,184,359,164 (file length)
11,240,476,672 (ntfs compressed file length)

time    file         method                                 disk 14:33?  compressed   fstream                                fixed disk 14:06   normal       fstream                                fixed disk 12:22   normal       winapi                                 fixed disk 11:47   compressed   winapi                                 fixed disk 11:29   compressed   fstream                                ram disk 10:37   compressed   winapi                                 ram disk  7:18   compressed   7z stored decompression ntfs 12gb   ram disk  6:37   normal       copy same volume                    fixed disk



the fstream constructor , access:

 define buffersize 524288     unsigned int mbytes = buffersize;     char * databuffer0; databuffer0 = (char*) malloc (mbytes);     datafile.open("drv:/file.ext", ios::in | ios::binary );     datafile.read (databuffer0, mbytes);


the winapi constructor , access:

 define buffersize 524288     unsigned int mbytes = buffersize;     const tchar* const filex = _t("drv:/file.ext");     char   readbuffer[buffersize] = {0};     hfile = createfile(filex, generic_read, file_share_read, null, open_existing, file_attribute_normal, null);     if( false == readfile(hfile, readbuffer, buffersize-1, &dwbytesread, null))     { ...

for fstream method, -> 16mb buffer sizes not decrease processing time. buffer sizes beyond .5mb fail winapi method. methods optimize implementation versus processing time?

did try memory-mapping file? in test fastest way read large files.

update: here's old, still accurate description of memory mapped files: http://msdn.microsoft.com/en-us/library/ms810613.aspx


Comments

Post a Comment

Popular posts from this blog

node.js - Bad Request - node js ajax post -

i'm using express 3.0 , node v0.11.0. have button submits form , i'm using ajax post data json object node server. client code is: $('#contact').submit(function(e) { console.log('submit called'); var formdata = json.stringify($('form').serializeobject()); console.log(formdata); $.ajax({ url: "http://localhost:3000/savedata/", type: "post", datatype: 'json', data: {objectdata: formdata}, contenttype: "application/json", complete: function() { console.log('process complete'); }, success: function(data) { console.log('process sucess'); }, error: function() { console.log('process error'); }, }); return false; }); then on server: var express = require('express'); var app = express(); app.set('views', __dirname + '/views'); app.set('view engine', 'jade'); app.use(express.bodyparser());...
Read more

Why does Ruby on Rails generate add a blank line to the end of a file? -

running rails generate controller foo home results in: class foocontroller < application controller def home end end (there's nothing on line in actual file, blank line) is there purpose blank line? it's common use newline indicate end of line, last line. many editors (like vi, use) add in newline silently. consensus text files (especially in unix world) should end in newline, , there have been problems historically if wasn't present. why should text files end newline? the tool used count lines in file "wc" counts newlines in file, without trailing newline show 3 instead of 4. it improves readability of templates used in generator. consider: https://github.com/rails/rails/blob/master/railties/lib/rails/generators/rails/controller/templates/controller.rb to remove trailing newline, template have last line of: end<% end -%> instead of: end <% end -%> that seems less readable me. the discussion below refers ...
Read more

keyboard - Smiles and long press feature in Android -

i've created android keyboard. how add features inserting smilies, , using long keypresses display symbols? to create long-press behavior allows select several options pop-up menu, follow guide (specifically pop-up menu section): http://developer.android.com/guide/topics/ui/menus.html smileys (also known emoticons) combination of keys, understood programs , parsed same way. have do, when clicks smiley face on keyboard, simulate pressing of key combination matching emoticon. example, when clicks smiley, should simulate key presses ':' , ')' :). here's list of emoticons: http://en.wikipedia.org/wiki/list_of_emoticons
Read more