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From Randall Leeds <randall.le...@gmail.com>
Subject Re: {error,emfile} on CouchDB 1.2.x
Date Sun, 18 Mar 2012 20:28:59 GMT
On Sun, Mar 18, 2012 at 11:08, Stefan Kögl <koeglstefan@gmail.com> wrote:

> Hi,
>
> Another thing I noticed during my tests of CouchDB 1.2.x. I redirected
> live traffic to the instance and after a rather short time, requests
> were failing with the following information in the logs:
>
>
> [Sun, 18 Mar 2012 16:39:24 GMT] [error] [<0.27554.2>]
> {error_report,<0.31.0>,
>                                    {<0.27554.2>,std_error,
>                                     [{application,mochiweb},
>                                      "Accept failed error",
>                                      "{error,emfile}"]}}
> [Sun, 18 Mar 2012 16:39:24 GMT] [error] [<0.27554.2>]
> {error_report,<0.31.0>,
>                          {<0.27554.2>,crash_report,
>                           [[{initial_call,
>                                 {mochiweb_acceptor,init,
>                                     ['Argument__1','Argument__2',
>                                      'Argument__3']}},
>                             {pid,<0.27554.2>},
>                             {registered_name,[]},
>                             {error_info,
>                                 {exit,
>                                     {error,accept_failed},
>                                     [{mochiweb_acceptor,init,3},
>                                      {proc_lib,init_p_do_apply,3}]}},
>                             {ancestors,
>                                 [couch_httpd,couch_secondary_services,
>                                  couch_server_sup,<0.32.0>]},
>                             {messages,[]},
>                             {links,[<0.129.0>]},
>                             {dictionary,[]},
>                             {trap_exit,false},
>                             {status,running},
>                             {heap_size,233},
>                             {stack_size,24},
>                             {reductions,244}],
>                            []]}}
>
>
> I think "emfile" means that CouchDB (or mochiweb?) couldn't open any
> more files / connections. I've set the (hard and soft) nofile limit for
> user couchdb to 4096, but didn't raise the ERL_MAX_PORTS accordingly.
> Anyway, as soon as the error occured, CouchDB started writing most of my
> view files from scratch, rendering the instance unusable.
>
> I'd expect CouchDB to fail more gracefully when the maximum number of
> open files is reached. Is this a bug or expected behaviour?
>

Looks like a bug. Whenever there's a problem opening a view file,
couch_view tries to delete it. Clearly, this is not the right course of
action when the problem is due to emfile.

Here's a patch that I propose might fix it. I'd like to hear from another
dev on this, or if there's a better way we should bail out.

diff --git a/src/couchdb/couch_view_group.erl
b/src/couchdb/couch_view_group.erl
index 97fc512..ab075bd 100644
--- a/src/couchdb/couch_view_group.erl
+++ b/src/couchdb/couch_view_group.erl
@@ -469,6 +469,10 @@ open_index_file(RootDir, DbName, GroupSig) ->
     case couch_file:open(FileName) of
     {ok, Fd}        -> {ok, Fd};
     {error, enoent} -> couch_file:open(FileName, [create]);
+    {error, emfile} ->
+        ?LOG_ERROR("Could not open file for view index: max open files
reached. "
+                   "Raise ERL_MAX_PORTS or system limits.", []),
+        throw({error, emfile});
     Error           -> Error
     end.

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