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From "Mike Wallace (JIRA)" <j...@apache.org>
Subject [jira] [Created] (COUCHDB-2425) Exceptions in couch_proc_manager:new_proc/1 leave dangling couch_query_servers
Date Fri, 31 Oct 2014 19:34:34 GMT
Mike Wallace created COUCHDB-2425:
-------------------------------------

             Summary: Exceptions in couch_proc_manager:new_proc/1 leave dangling couch_query_servers
                 Key: COUCHDB-2425
                 URL: https://issues.apache.org/jira/browse/COUCHDB-2425
             Project: CouchDB
          Issue Type: Bug
      Security Level: public (Regular issues)
          Components: Database Core
            Reporter: Mike Wallace


If an exception is thrown in the try blocks in either of the couch_proc_manager:new_proc/1
clauses [1] [2] then a spawn_error is returned which is handled by a specific handle_info
clause [3] which does not reply to the calling process. When the caller is couch_query_servers:get_os_process/1
[4] there is an infinite timeout so that process will hang around until either the node reboots
or someone intervenes.

The user-facing symptom is an entry in _active_tasks that makes no progress and never goes
away.

The easiest way to reproduce this is to create a new view and then patch the code to force
an exception in the appropriate place, e.g.: (assuming a live dev/run instance): 

 1. Create DB, add a ddoc and a doc:
{code}
$ curl -X PUT http://localhost:15984/kitteh
{"ok":true}
$ curl -X POST http://localhost:15984/kitteh -d '{"_id":"_design/view", "views": {"test":
{"map": "function(doc) { emit(doc.id, 1); }"}}}' -H 'Content-Type: application/json'
{"ok":true,"id":"_design/view","rev":"1-ef10f980522d4c8e691e3c26d4c3fac5"}
$ curl -X PUT http://localhost:15984/kitteh/ohai -d '{}'
{"ok":true,"id":"ohai","rev":"1-967a00dff5e02add41819138abb3284d"}
{code}

 2. Apply https://gist.github.com/mikewallace1979/79f823da25f6a78e2725 then re-run make and
dev/run.

 3. Attempt to query the view:
{code}
$ curl -X GET http://localhost:15984/kitteh/_design/view/_view/test
{"error":"timeout","reason":"The request could not be processed in a reasonable amount of
time."}
{code}

 4. Observe index build tasks which never go away:
{code}
$ curl -X GET http://localhost:15986/_active_tasks
[{"pid":"<0.2403.0>","changes_done":0,"database":"shards/40000000-5fffffff/kitteh.1414779043","design_document":"_design/view","progress":0,"started_on":1414779439,"total_changes":1,"type":"indexer","updated_on":1414779439},{"pid":"<0.2444.0>","changes_done":0,"database":"shards/00000000-1fffffff/kitteh.1414779043","design_document":"_design/view","progress":0,"started_on":1414779439,"total_changes":1,"type":"indexer","updated_on":1414779439}]
{code}

[1] https://github.com/apache/couchdb-couch/blob/master/src/couch_query_servers.erl#L354

[2] https://github.com/apache/couchdb-couch/blob/master/src/couch_proc_manager.erl#L368-L384

[3] https://github.com/apache/couchdb-couch/blob/master/src/couch_proc_manager.erl#L239-L245

[4] https://github.com/apache/couchdb-couch/blob/master/src/couch_query_servers.erl#L354



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