Safe stream update of file

Question

We perform updates of large text files by writing new records to a temp file, then replacing the old file with the temp file. A heavily abbreviated version:

Answer 1

The normal way of avoiding the "delete then move fails problem" is:

• Write to file.new
• Move file.current to file.old
• Move file.new to file.current
• Delete file.new

Then when you come to read, use file.new if file.current is missing, deleting file.old if you see it.

Checking for whether or not the file is available: try opening it for write, but appending to the end. Of course, you'll need to close the handle before you then move it, and in-between someone else could open it - but it would at least be a reasonable optimisation.

Not sure about copying summaries etc, I'm afraid.