couchdb-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Paul Davis <paul.joseph.da...@gmail.com>
Subject Re: Fsyncgate: errors on fsync are unrecovarable
Date Sun, 21 Jul 2019 17:23:43 GMT
I’m browsing on my phone but I’m pretty sure we should add an `ok =` to
this line so that we force a bad match:

https://github.com/apache/couchdb/blob/9d098787a71d1c7f7f6adea05da15b0da3ecc7ef/src/couch/src/couch_file.erl#L223

Unless I’m missing somewhere else that we’re making that assertion.

On Sun, Jul 21, 2019 at 4:21 AM Jan Lehnardt <jan@apache.org> wrote:

> Hey all,
>
>
> Joan sent this along in IRC and it reads bad enough[tm] that we should at
> least have a few pairs of eyes looking at if we have to do anything:
>
>     http://danluu.com/fsyncgate/
>
> (It is long and dense, you’ll need to read 10-15% of that page to get the
> main picture.
>
> tl;dr: running fsync() after an fsync() that reported EIO clears that
> error state with no way of recovery on Linux.
>
> There are two ways of handling this correctly:
>
> 1. whatever you wrote() between the last successful fsync() and the
> fsync() that raised the error, keep around until after the second fsync(),
> so you can write() it again.
>
> 2. if any one fsync() returns EIO, report this back up immediately, so
> whoever calls you can retry.
>
> * * *
>
> We seem to be doing 2. as per my reading.
>
> Erlang looks like it correctly just raises whatever error fsync() might
> return:
>
> 1.
> https://github.com/erlang/otp/blob/maint-r14/erts/emulator/drivers/unix/unix_efile.c#L792-L809
> 2.
> https://github.com/erlang/otp/blob/maint-r14/erts/emulator/drivers/unix/unix_efile.c#L151-L163
>
> couch_file too:
>
> 1.
> https://github.com/apache/couchdb/blob/master/src/couch/src/couch_file.erl#L215-L223
>
> I glanced at a few paths going up this chain and couldn’t spot a catch
> where we’d hide that error, but it’d be great to get some confirmation on
> this.
>
> * * *
>
> Please double-check my understanding of the issue, the correct ways
> forward and the findings in Erlang and CouchDB.
>
> Best
> Jan
> --
> Professional Support for Apache CouchDB:
> https://neighbourhood.ie/couchdb-support/
>
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message