Re: NSDocument save incremental file package in-place
Re: NSDocument save incremental file package in-place
- Subject: Re: NSDocument save incremental file package in-place
- From: Quincey Morris <email@hidden>
- Date: Sat, 01 Mar 2014 09:43:22 -0800
On Mar 1, 2014, at 07:23 , Trygve Inda <email@hidden> wrote:
> The problem is that when there is a very small change (just adding or
> removing one of the files in the package), the system does not save in
> place.
>
> Rather it reads the previous package file completely, writes out a copy of
> the package (400 MB) and then renames it.
>
> How can I get it to save in place?
AFAIK, NSDocument never saves in place, and isn’t intended to (for safety reasons — what happens if your app crashes after some of the files have been updated but not others?).
Instead, it achieves its package performance optimization by hard-linking unchanged files in the new (saved) package to files in the old (original) package. If your save is taking 40 seconds, that could mean:
— The document is on a file system that doesn’t support hard linking.
— The document is on a file system where hard linking 7500 files takes 40 seconds.
— You didn’t preserve the original file sub-wrappers from the directory wrapper created when the document was opened, so NSDocument thinks all the files have changed. Note that it’s undocumented (again, AFAIK) what criteria NSDocument uses** to decide when a particular file wrapper represents “no change”, so it’s safest to keep the original NSFileWrapper objects from open time until save time.
** The most likely possibilities are ‘==’ on file wrappers, ‘isEqual:’ on file wrappers, or comparison of mod date and/or size of the actual files, but it could be something more obscure.
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