[COUCHDB-1171] Multiple requests to _changes feed causes {error, system_limit} "Too many processes"

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.0.2, 1.0.3, 1.1
• Fix Version/s: 1.0.3, 1.1, 1.2
• Skill Level: New Contributors Level (Easy)
• Assignee: Robert Newson
• Reporter: Alexander Shorin
• Created: 19/May/11 15:15
• Updated: 29/Jun/11 21:26
• Resolved: 29/Jun/11 21:26

Description

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.