Hi Hitoshi,
I have missed some important code in queue_peer_request(). The function
has the following code:
if (req->rq.flags & SD_FLAG_CMD_RECOVERY)
req->rq.epoch = req->rq.obj.tgt_epoch;
At last, epoch and tgt_epoch has the same value. So it it not a bug. I'm
sorry about my mistake.
Bingpeng
------------------ Original ------------------
From: "Hitoshi Mitake";<[email protected]>;
Date: Sat, May 30, 2015 06:11 PM
To: "Bingpeng Zhu"<[email protected]>;
Cc: "sheepdog"<[email protected]>;
Subject: Re: [sheepdog] question about the epoch field in reading peer request
header
At Sat, 30 May 2015 01:12:12 +0800,
=?ISO-8859-1?B?QmluZ3BlbmcgWmh1?= wrote:
>
> [1 <multipart/alternative (8bit)>]
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> Hi all:
> I have a problem about the epoch information in SD_OP_READ_PEER request
> header. I'm not sure whether I misunderstand the code or it is a bug.
> When we recover a erasure code object in recovery, we need to read the
> remaining replicas firstly to rebuild the lost replica. In function
> read_erasure_object(), we init SD_OP_READ_PEER request header by the
> following code:
>
>
> sd_init_req(&hdr, SD_OP_READ_PEER);
> hdr.epoch = epoch;
> hdr.flags = SD_FLAG_CMD_RECOVERY;
> hdr.data_length = rlen;
> hdr.obj.oid = oid;
> hdr.obj.tgt_epoch = tgt_epoch;
> hdr.obj.ec_index = idx;
>
>
>
> I think hdr.epoch is current epoch of the cluster and hdr.obj.tgt_epoch
> is the historical epoch from which we want to read the stale replica. The
> target node will call peer_read_obj() to process SD_OP_READ_PEER request.
> Peer_read_obj() set iocb.epoch = hdr->epoch then pass iocb to
> sd_store->read(). In default_read(), we use iocb->epoch < sys_epoch() to
> judge whether the request is againt the older epoch which needs to read
> replica from the stale directory. I think we use the wrong epoch here. We
> should use hdr.obj.tgt_epoch rather than hdr.epoch to make the judgement. Can
> anyone answer my question?
Hi Bingpeng,
Thanks for your pointing! Your argument seems to be right. We need to
use tgt_epoch. The problem seems to be shared with recovyer process of
ordinal replicated object.
Could you send a patch for solving this problem?
Thanks,
Hitoshi
>
>
> Thanks.
> Bingpeng
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