vector write/read

[Alan Bateman]

Tigran Mkrtchyan wrote:
> Hi,
>
>
> just want to ask why vector operations are not a part to nio?
>
> we are working on distributed storage and our users  often know where 
> data is (files are like small databases - header and records). We have 
> our own protocol for it and extensions to posix IO api:
>
> typedef struct {
>     off64_t offset;
>     int len;
>     char *buf;
> } iovec2;
>
> extern int     dc_readv2(int, iovec2 *, int);
>
> Basically what it does is you give an array of buffers and for each 
> buffer you provide an offset. It's very helpful when there is a lot of 
> randomly distributed small records. If file system do not support it 
> you can always fall back to 'classic' reads internally, but provide 
> only classic API force other people to find some custom solutions.
Right, vector I/O is not currently supported, and for your example, 
would require a sequence of reads (or you could use a thread pool to get 
some parallelism or use AsynchronousFileChannel). I haven't seen many 
requests for this but it may be worth considering. Off-hand, I don't 
know if this is an area that has been standarized (the closest that 
comes to mind is lio_listio in the real-time extensions when used in 
wait mode).

-Alan.