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From Pasi Eronen ...@iki.fi>
Subject Re: CouchDB 1.0.2 errors under load
Date Sat, 26 Feb 2011 00:31:53 GMT
Yes, the client is doing something funky :-) Many of the requests
it sends are POSTs with chunked transfer encoding, so it's being
hit hard by issue COUCHDB-682. In other words, there's lot of closing
and opening of TCP connections going on, and retrying requests that
failed due to COUCHDB-682.

(The server behavior in COUCHDB-682 is probably strictly speaking not
violating the HTTP spec -- the server is allowed to close an idle persistent
connection at any time -- but it's certainly causing unusual behavior
vs. opening and closing of TCP connections.)

Output from netstat -anp looks like this:

tcp  1  0  127.0.0.1:5984  127.0.0.1:51681  CLOSE_WAIT  19124/beam.smp
tcp  1  0  127.0.0.1:5984  127.0.0.1:36576  CLOSE_WAIT  19124/beam.smp
tcp  1  0  127.0.0.1:5984  127.0.0.1:35311  CLOSE_WAIT  19124/beam.smp
(...)

The other directions (e.g. 127.0.0.1:51681 -> 127.0.0.1:5984) are no longer
around (if they would be, I guess the client would also run out of fds --
and
the number of fds used by the client is not growing).

Does this offer any clues for diagnosing the bug?

I can also try if I can reproduce the fd leak with some simple test
program...

Best regards,
Pasi

On Sat, Feb 26, 2011 at 01:11, Paul Davis <paul.joseph.davis@gmail.com>
wrote:
> It sounds like your client is doing something funky with shutting down
> connections to the server. If I were to guess I would say that it
> looks like you're leaking sockets between a call to shutdown and a
> call to close. Though to say for certain I'd need to see what state
> both ends of the socket are in.
>
> The errors about pread_iolist are hard to diagnose without the
> surrounding error messages but if I were to guess is that you're
> getting an emfile that cascades to the file gen_server which then
> notifies other people trying to issue read calls.
>
> On Fri, Feb 25, 2011 at 5:43 PM, Pasi Eronen <pe@iki.fi> wrote:
>> Thanks! I looked at /proc/(pid-of-beam.smp)/fd, and it seems CouchDB
>> is indeed using a lot of file descriptors, and the number is growing.
>> I restarted CouchDB (and my batch job), and after 40 minutes, it was
>> already using 300 fds; an hour later, the figure was 600; half
>> an hour later, almost 700.
>>
>> The default "ulimit -n" was 1024, so that adds up to couple of hours.
>> As a temporary fix I changed the limit to 64K, so it should work fine
>> for the weekend :-) (but not much longer)
>>
>> Based on "netstat -an", the fds are TCP connections stuck in CLOSE_WAIT
>> state. Hmm. It seems CLOSE_WAIT means the client closed the connection
>> but CouchDB didn't call close() to release the fd? And that's presumably
>> a bug somewhere in CouchDB, right?
>>
>> After the initial error message, the log had ~300 almost identical
>> error messages of the form (with different number after pread_iolist):
>>
>> [Thu, 24 Feb 2011 19:42:57 GMT] [error] [<0.31510.2>]
>> Uncaught error in HTTP request: {exit,
>>                                 {normal,
>>                                  {gen_server,call,
>>                                   [<0.288.0>,
>>                                    {pread_iolist,812881959},
>>                                    infinity]}}}
>>
>> Does this give any hints where the bug might be?
>>
>> If not, I'll see if I can reproduce the bug somehow in more controlled
>> setting. (I have a hunch that this might involve the use of HTTP
>> expect/continue or POST requests with chunked transfer encoding,
>> but let's see....)
>>
>> Best regards,
>> Pasi
>>
>> On Fri, Feb 25, 2011 at 19:01, Paul Davis <paul.joseph.davis@gmail.com>
wrote:
>>> On Fri, Feb 25, 2011 at 4:18 AM, Pasi Eronen <pe@iki.fi> wrote:
>>>> Hi,
>>>>
>>>> I had a big batch job (inserting 10M+ documents and generating views
for them)
>>>> that ran just fine for about 6 hours, but then I got this error:
>>>>
>>>> [Thu, 24 Feb 2011 19:42:57 GMT] [error] [<0.276.0>] ** Generic server
>>>> <0.276.0> terminating
>>>> ** Last message in was delayed_commit
>>>> ** When Server state ==
{db,<0.275.0>,<0.276.0>,nil,<<"1298547642391489">>,
>>>>                            <0.273.0>,<0.277.0>,
>>>>                            {db_header,5,739828,0,
>>>>                                {4778613011,{663866,0}},
>>>>                                {4778614954,663866},
>>>>                                nil,0,nil,nil,1000},
>>>>                            739828,
>>>>                            {btree,<0.273.0>,
>>>>                                {4778772755,{663866,0}},
>>>>                                #Fun<couch_db_updater.7.10053969>,
>>>>                                #Fun<couch_db_updater.8.35220795>,
>>>>                                #Fun<couch_btree.5.124754102>,
>>>>                                #Fun<couch_db_updater.9.107593676>},
>>>>                            {btree,<0.273.0>,
>>>>                                {4778774698,663866},
>>>>                                #Fun<couch_db_updater.10.30996817>,
>>>>                                #Fun<couch_db_updater.11.96515267>,
>>>>                                #Fun<couch_btree.5.124754102>,
>>>>                                #Fun<couch_db_updater.12.117826253>},
>>>>                            {btree,<0.273.0>,nil,
>>>>                                #Fun<couch_btree.0.83553141>,
>>>>                                #Fun<couch_btree.1.30790806>,
>>>>                                #Fun<couch_btree.2.124754102>,nil},
>>>>                            739831,<<"foo_replication_tmp">>,
>>>>
 "/data/foo/couchdb-data/foo_replication_tmp.couch",
>>>>                            [],[],nil,
>>>>                            {user_ctx,null,[],undefined},
>>>>                            #Ref<0.0.1793.256453>,1000,
>>>>                            [before_header,after_header,on_file_open],
>>>>                            false}
>>>> ** Reason for termination ==
>>>> ** {{badmatch,{error,emfile}},
>>>>    [{couch_file,sync,1},
>>>>     {couch_db_updater,commit_data,2},
>>>>     {couch_db_updater,handle_info,2},
>>>>     {gen_server,handle_msg,5},
>>>>     {proc_lib,init_p_do_apply,3}]}
>>>>
>>>> (+lot of other messages with the same timestamp -- can send if they're
useful)
>>>>
>>>> Exactly at this time, the client got HTTP 500 status code; the request
>>>> was a bulk get (POST /foo_replication_tmp/_all_docs?include_docs=true).
>>>>
>>>> Just before this request, the client had made a PUT (updating an
existing
>>>> document) that got 200 status code, but apparently was not successfully
>>>> committed to the disk (I'm using "delayed_commits=true" - for my app,
>>>> this is just fine). The client had received the new _rev value, but
when
>>>> it tried updating the same document a minute later, there was a
conflict
>>>> (and it's not possible that somebody else updated this same document).
>>>>
>>>> About four hours later, there was a different error ("accept_failed"
>>>> sounds like some temporary problem with sockets?):
>>>>
>>>> [Thu, 24 Feb 2011 23:55:42 GMT] [error] [<0.20693.4>]
{error_report,<0.31.0>,
>>>>              {<0.20693.4>,std_error,
>>>>               [{application,mochiweb},
>>>>                "Accept failed error","{error,emfile}"]}}
>>>>
>>>> [Thu, 24 Feb 2011 23:55:42 GMT] [error] [<0.20693.4>]
{error_report,<0.31.0>,
>>>>    {<0.20693.4>,crash_report,
>>>>
[[{initial_call,{mochiweb_socket_server,acceptor_loop,['Argument__1']}},
>>>>       {pid,<0.20693.4>},
>>>>       {registered_name,[]},
>>>>       {error_info,
>>>>           {exit,
>>>>               {error,accept_failed},
>>>>               [{mochiweb_socket_server,acceptor_loop,1},
>>>>                {proc_lib,init_p_do_apply,3}]}},
>>>>       {ancestors,
>>>>
[couch_httpd,couch_secondary_services,couch_server_sup,<0.32.0>]},
>>>>       {messages,[]},
>>>>       {links,[<0.106.0>]},
>>>>       {dictionary,[]},
>>>>       {trap_exit,false},
>>>>       {status,running},
>>>>       {heap_size,233},
>>>>       {stack_size,24},
>>>>       {reductions,200}],
>>>>      []]}}
>>>>
>>>> (+lots of other messages within the next couple of minutes)
>>>>
>>>> The same error occured once more, about four hours later.
>>>>
>>>> I'm quite new to CouchDB, so I'd appreciate any help in interpreting
>>>> what these error messages mean. (BTW, are these something I should
>>>> report as bugs in JIRA? I can do that, but I'd like to at least
understand
>>>> which parts of the error messages are actually relevant here :-)
>>>>
>>>> I'm running CouchDB 1.0.2 with Erlang R14B on 64-bit RHEL 5.6.
>>>>
>>>> Best regards,
>>>> Pasi
>>>>
>>>
>>> The error you're getting is because CouchDB is running out of
>>> available file descriptors to use. Try increasing the limit for the
>>> user running CouchDB.
>>>
>>
>

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