using mmap on large (> 2 Gig) files
Thu Oct 26 06:41:05 CEST 2006
"sturlamolden" <sturlamolden at yahoo.no> writes:
> However, "memory mapping" a file by means of fseek() is probably more
> efficient than using UNIX' mmap() or Windows'
Why on would you think that?! It is counterintuitive. fseek beyond
whatever is buffered in stdio (usually no more than 1kbyte or so)
requires a system call, while mmap is just a memory access.
> In Python, we don't always need the file memory mapped, we normally
> just want to use slicing-operators, for-loops and other goodies on
> the file object -- i.e. we just want to treat the file as a Python
> container object. There are many ways of achieving that.
Some of the time we want to share the region with other processes.
Sometimes we just want random access to a big file on disk without
having to do a lot of context switches seeking around in the file.
> There are in any case room for improving Python's mmap object.
IMO it should have some kind of IPC locking mechanism added, in
addition to the offset stuff suggested.
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