Subject: Re: pread() over NFS (again) [1.5.5.4]

From: Junio C Hamano <[email-masked]>
Date: Thu, 26 Jun 2008 16:38:40 -0700

[email-masked] writes:

> On Jun 26, 2008, at 1:56 PM, Junio C Hamano wrote:
>
>>> "The file shouldn't be short unless someone truncated it, or there
>>> is a bug in index-pack.  Neither is very likely, but I don't think
>>> we would want to retry pread'ing the same block forever.
>>
>> I don't think we would want to retry even once.  Return value of 0
>> from
>> pread is defined to be an EOF, isn't it?
>
> No, it seems to be a simple error-out in this case. We have 2.4.20
> systems with nfs-utils 0.3.3 and used to frequently get the same error
> while pushing. I made a similar change back in February and haven't
> had a problem since:
>
> diff --git a/index-pack.c b/index-pack.c
> index 5ac91ba..85c8bdb 100644
> --- a/index-pack.c
> +++ b/index-pack.c
> @@ -313,7 +313,14 @@ static void *get_data_from_pack(struct
> object_entry *obj)
> 	src = xmalloc(len);
> 	data = src;
> 	do {
> +		// It appears that if multiple threads read across NFS, the
> +		// second read will fail. I know this is awful, but we wait for
> +		// a little bit and try again.
> 		ssize_t n = pread(pack_fd, data + rdy, len - rdy, from + rdy);
> +		if (n <= 0) {
> +			sleep(1);
> +			n = pread(pack_fd, data + rdy, len - rdy, from + rdy);
> +		}
> 		if (n <= 0)
> 			die("cannot pread pack file: %s", strerror(errno));
> 		rdy += n;
>
> I use a sleep request since it seems less likely that the other thread
> will have an outstanding request after a second of waiting.

Gaah.  Don't we have NFS experts in house?  Bruce, perhaps?