I am storing documents in sql server in varbinary(max) fileds, I use filestream optionally when a user has:
(DB_Size + Docs_Size) ~> 0.8 * ExpressEdition_Max_DB_Size
I am currently zipping all the files, anyway this is done because the Document Read/Write work was developed 10 years ago where Storage was more expensive than now.
Many files when zipped are almost as big as the original (a zipped pdf is about 95% of original size). And anyway unzipping has some overhead, that becomes twice when I need also to "Check-in"/Update the file because I need to zip it.
So I was thinking of giving to the users the option to choose whether the file type will be zipped or not by providing some meaningful default values. For my experience I would impose the following rules:
1) zip by default: txt, bmp, rtf
2) do not zip by default: jpg, jpeg, Microsoft Office files, Open Office files, png, tif, tiff
Could you suggest other file types chosen among the most common or comment on the ones I listed here?
.doc and .mdb files actually tend to compress rather well, if i remember correctly. The Office 2007 equivalents (.docx and .accdb), though, are zip files already...so compressing them is pretty much useless.
Don't forget HTML and XML files. Zip by default.
I commend you on being able to recognize what are and aren't compressed file types. You probably already understand this, but I'll rant here:
Do not double-up compression methods! Each compression method adds its own header adding to file size, and since the data has already had its statistical redundancies eliminated as best as it could by one method, it's probably not going to be able to compressed further via another method. Take this set of files for example:
46,494,380 level0.wav
43,209,258 level1.wav.zip
43,333,266 level2.wav.zip.rar
43,339,894 level3.wav.zip.rar.gz
43,533,989 level4.wav.zip.rar.gz.bz2
All of these files contain the same data.
The first compression method worked well to eliminate redundancies, but each successive compression method just added to the file size, not to mention the headache of decrypting the file later.
The best method of compression is usually the first one applied.
28,259,406 level1.wav.flac <~ using a compression method meant for the file.
Related
For example, if we have the following file: file.txt that after the compression is now file.new (new is the new extension) , how to obtain that .txt extension, that is forgotten?
I need that to decompress the file.
In general, if you lose the file name extension you can't get it back. It's as simple as this.
However, there might be chances depending on the compression format. Some formats do store the original file name (along with other informations) in the compressed file. And the "decompressor" will be able to recreate those properties.
Anyway, it's good practise to name a compressed file with an additional extension, in your case file.txt.new.
Oh, and you don't need to know the file name extension to uncompress the compressed file. Just uncompress it and give it a temporary name. As #MarcoBonelli said, file contents and file name extensions have no fixed relation. They are just a convention to handle them conveniently.
For example: You can rename a EXE to DOCX. Windows will show the Word icon but it is still an executable. Windows will not attempt to run it, though.
To know what a file contains can be difficult. The magic number Marco linked to might give you some hint.
I need to store data in a file in this format
word, audio, jpeg
How would I store that all in one file? Is it even possible do would I need to store links to other data files in place of the audio and jpeg. Would I need a custom file format?
1. Your own filetype
As mentioned by #Ken White you would need to be creating your own custom file format for this sort of thing, which would then mean creating your own parser type. This could be achieved in almost any language you wanted but since you are planning on using word format, then maybe C# would be best for you. However, this technique could be quite complicated and take a relatively large amount of time to thoroughly test your file compresser / decompressor, but may be best depending on your needs.
2. Command line utilities
Another way to go about this would be to use a bash script to combine all of the files into one file, and then decompress it at the other end. For example the steps could involve:
Combine files using windows copy / linux cat command on command line
Create a metdata file of your own that says how many files are in this custom file, and how much memory each one takes up (could be a short XML or JSON file for example...)
Use the linux split command or install a Windows command line file splitter program (here's just one example) to split the file back into whatever components have made it up.
This way you only have to create a really small file type, and let the OS utilities handle the combining of them for you.
Example on Windows:
Copy all of the files in your current directory into one output file called 'file.custom'
copy /b * file.custom
Generate custom file format describing metadata (i.e. get the file size on disk in C# example here). This is just maybe what I would do in JSON. SO formatting was being annoying so here's a link (Copy paste it into an editor or online JSON viewer).
Use a decompress windows / linux command line tool to decompress each files to the exact length (and export it back to the exact name) specified in the JSON (metadata) file. (More info on splitting files on this post).
3. ZIP files
You could always store all of the files in a compressed zip file, and then just use a zip compressor, expander as and when you like to retreive any number of file formats stored within.
I found a couple of examples of :
Combining multiple files into one ZIP file in only C# .net,
Unzipping ZIP files in C#
Zipping & Unzipping with only windows built-in utilities
Zipping & Unzipping in Linux command line
Good Zipping/Unzipping library in Java
Zipping/Unzipping in Python
I have large zip files that contain huge files. There are "metadata" text files within the zip archives that need to be modified. However, it is not possible to extract the entire zip and re-compress it. I need to locate the target text file inside the zip, edit it, and possibly append the change to the zip file. The file name of the text file is always the same, so it can be hard-coded. Is this possible? Is there a better way?
There are two approaches. First, if you're just trying to avoid recompression of the entire zip file, you can use any existing zip utility to update a single file in the archive. This will entail effectively copying the entire archive and creating a new one with the replaced entry, then deleting the old zip file. This will not recompress the data not being replaced, so it should be relatively fast. At least, about the same time required to copy the zip archive.
If you want to avoid copying the entire zip file, then you can effectively delete the entry you want to replace by changing the name within the local and central headers in the zip file (keeping the name the same length) to a name that you won't use otherwise and that indicates that the file should be ignored. E.g. replacing the first character of the name with a tilde. Then you can append a new entry with the updated text file. This requires rewriting the central directory at the end of the zip file, which is pretty small.
(A suggestion in another answer to not refer to the unwanted entry in the central directory will not necessarily work, depending on the utility being used to read the zip file. Some utilities will read the local headers for the zip file entry information, and ignore the central directory. Other utilities will do the opposite. So the local and central entry information should be kept in sync.)
There are "metadata" text files within the zip archives that need to be modified.
However, it is not possible to extract the entire zip and re-compress it.
This is a good lesson why, when dealing with huge datasets, keeping the metadata in the same place with the data is a bad idea.
The .zip file format isn't particularly complicated, and it is definitely possible to replace something inside it. The problem is that the size of the new data might increase, and not fit anymore into the location of the old data. Thus there is no standard routine or tool to accomplish that.
If you are skilled enough, theoretically, you can create your own zip handling functions, to provide the "file replace" routine. If it is about the (smallish) metadata, you do not even need to compress them. The .zip's "central directory" is located in the end of the file, after the compressed data (the format was optimized for appending new files). General concept is: read the "central directory" into the memory, append the new modified file after the compressed data, update the central directory in memory with the new file offset of the modified file, and write the central directory back after the modified file. (The old file would be still sitting somewhere inside the .zip, but not referenced anymore by the "central directory".) All the operations would be happening at the end of the file, without touching the rest of the archive's content.
But practically speaking, I would recommend to simply keep the data and the metadata separately.
Using 7zip I compressed ~15GB worth of pictures split in folders in 15 1024MB files.
Compression methode: LZMA2; Level: Ultra; Dictionary size: 64M;
At the end of compression some of the files had their "last modified" time changed to the time of completion, while some of the files didn't.
Why is this?
And if I have already uploaded most of the files will I be able to unarchive them successfully?
You would need to ask the author of the program for an explanation of why it modifies volumes at the end of the operation. If I had to make an educated guess, it might be because 7-zip doesn't know which is the last volume until it's finished (because this would depend on the compression ratio of the files being archived, which can't be predicted), and so it needs to go back and update parts of the volume file headers accordingly.
In general, though, quoting the relevant 7-zip help file entry:
NOTE: Please don't use volumes (and don't copy volumes) before
finishing archiving. 7-Zip can change any volume (including first
volume) at the end of archiving operation.
The only safe assumption is that you can't reliably use any of your individual 1GB volumes until 7-zip has finished processing the whole 15GB archive.
After hours on Google I cant find any good reference info on the .CNDF file format for Satellite channel lists stored on Sat box's.
I do know that there is .NDF (uncompressed) & .CNDF (Compressed) versions of the file format.
I basically want to open & un-compress the .CNDF file in my C# app, play around with it, then compress and save it out again.
Any pointers to the file format data sheet or any decent examples, especially the compression method used. Thanks