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From "Alexander Shorin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (COUCHDB-1171) Multiple requests to _changes feed causes {error, system_limit} "Too many processes"
Date Sat, 21 May 2011 09:28:47 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-1171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13037294#comment-13037294
] 

Alexander Shorin commented on COUCHDB-1171:
-------------------------------------------

That's the question, because there is no such behavior for all other resources: chunked lists,
attachments, shows, views etc. I know, that I could simply extend Erlang processes count,
but this wouldn't be default configuration "from the box" and looks like workaround, but not
a solution. I don't know Erlang specifics and may be wrong, but could this behavior be used
for somekind DoS attacks? Just to crush not CouchDB itself, but related applications which
wouldn't expect this error.

> Multiple requests to _changes feed causes {error, system_limit} "Too many processes"
> ------------------------------------------------------------------------------------
>
>                 Key: COUCHDB-1171
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-1171
>             Project: CouchDB
>          Issue Type: Bug
>    Affects Versions: 1.0.2, 1.0.3, 1.1
>            Reporter: Alexander Shorin
>
> Originally I have investigated of issue 182 of couchdb-python package where calling db.changes()
function over 32768 times generates next messages in CouchDB log:
> [Thu, 19 May 2011 14:03:26 GMT] [info] [<0.2909.0>] 127.0.0.1 - - 'GET' /test/_changes
200
> [Thu, 19 May 2011 14:03:26 GMT] [error] [emulator] Too many processes
> [Thu, 19 May 2011 14:03:26 GMT] [error] [<0.2909.0>] Uncaught error in HTTP request:
{error,system_limit}
> [Thu, 19 May 2011 14:03:26 GMT] [info] [<0.2909.0>] Stacktrace: [{erlang,spawn,
>                      [erlang,apply,
>                       [#Fun<couch_stats_collector.1.123391259>,[]]]},
>              {erlang,spawn,1},
>              {couch_httpd_db,handle_changes_req,2},
>              {couch_httpd_db,do_db_req,2},
>              {couch_httpd,handle_request_int,5},
>              {mochiweb_http,headers,5},
>              {proc_lib,init_p_do_apply,3}]
> [Thu, 19 May 2011 14:03:26 GMT] [info] [<0.2909.0>] 127.0.0.1 - - 'GET' /test/_changes
500
> More info about this issue could be found there: http://code.google.com/p/couchdb-python/issues/detail?id=182
> However, I still couldn't reproduce this error using only httplib module, but I've got
that same behavior using feed=longpool option:
> from httplib import HTTPConnection
> def test2():
>     conn = HTTPConnection('localhost:5984')
>     conn.connect()
>     i = 0
>     while(True):
>         conn.putrequest('GET', '/test/_changes?feed=longpool')
>         conn.endheaders()
>         conn.getresponse().read()
>         i = i + 1
>         if i % 100 == 0:
>             print i
> When i get's around 32667 exception raises
> Traceback (most recent call last):
>   File "/home/kxepal/projects/couchdb-python/issue-182/test.py", line 259, in <module>
>     test2()
>   File "/home/kxepal/projects/couchdb-python/issue-182/test.py", line 239, in test2
>     resp.read()
>   File "/usr/lib/python2.6/httplib.py", line 522, in read
>     return self._read_chunked(amt)
>   File "/usr/lib/python2.6/httplib.py", line 565, in _read_chunked
>     raise IncompleteRead(''.join(value))
> httplib.IncompleteRead: IncompleteRead(0 bytes read)
> [Thu, 19 May 2011 14:10:20 GMT] [info] [<0.3240.4>] 127.0.0.1 - - 'GET' /test/_changes?feed=longpool
200
> [Thu, 19 May 2011 14:10:20 GMT] [error] [emulator] Too many processes
> [Thu, 19 May 2011 14:10:20 GMT] [error] [<0.3240.4>] Uncaught error in HTTP request:
{error,system_limit}
> [Thu, 19 May 2011 14:10:20 GMT] [info] [<0.3240.4>] Stacktrace: [{erlang,spawn,
>                      [erlang,apply,
>                       [#Fun<couch_stats_collector.1.123391259>,[]]]},
>              {erlang,spawn,1},
>              {couch_httpd_db,handle_changes_req,2},
>              {couch_httpd_db,do_db_req,2},
>              {couch_httpd,handle_request_int,5},
>              {mochiweb_http,headers,5},
>              {proc_lib,init_p_do_apply,3}]
> [Thu, 19 May 2011 14:10:20 GMT] [info] [<0.3240.4>] 127.0.0.1 - - 'GET' /test/_changes?feed=longpool
500
> Same error. I know, that test function is quite outside from real use case, but is this
correct behavior and couldn't it be used in malicious aims?
> This exception occurres only for multiple requests within single connection for changes
feed, chunked lists or attachments are not affected, if I've done all right.
> Test environment:
> Gentoo Linux 2.6.38
> CouchDB 1.0.2 release
> couchdb-python@63feefd9e3b6
> Python 2.6.6
> If there is needed some additional information I could try to provide it.

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