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https://issues.apache.org/jira/browse/COUCHDB-567?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12776817#action_12776817
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Paul Joseph Davis commented on COUCHDB-567:
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Sean,
I don't see anything in the SVN logs that affected couch_os_process.erl,
couch_native_process.erl or couch_query_servers.erl that's not in the about to
be released 0.10.1. And I'm pretty sure that all of these commits were in
0.10.0. If you can't reproduce on trunk, you should be able to just copy that
js test file to your Futon directory and see if it can be triggered on 0.10.0
though that would be most odd.
> Erlang View with Reduce Fails on Large Number of documents
> ----------------------------------------------------------
>
> Key: COUCHDB-567
> URL: https://issues.apache.org/jira/browse/COUCHDB-567
> Project: CouchDB
> Issue Type: Bug
> Affects Versions: 0.10
> Reporter: Sean Geoghegan
> Attachments: generate-data.rb, view.erl
>
>
> I have been having a problem with running Erlang views over a large dataset.
> Whenever the indexer goes to checkpoint it's process the following error
> occurs:
> ** Last message in was {'EXIT',<0.2220.0>,
> {function_clause,
> [{couch_view_updater,view_insert_doc_query_results,
> [{doc,<<"73956fdca62c384849a3313e6c48b7ed">>,...
> [],
> [{{view,0,
> [<<"_temp">>],
> <<"...">>,
> {btree,<0.2218.0>,
> {1565615,{341,[0]}},
> #Fun<couch_btree.3.83553141>,
> #Fun<couch_btree.4.30790806>,
> #Fun<couch_view.less_json_keys.2>,
> #Fun<couch_view_group.11.46347864>},
> [{<<"_temp">>,
> <<"...">>}]},
> []}],
> [],[]]},
> {couch_view_updater,view_insert_query_results,4},
> {couch_view_updater,process_doc,4},
> {couch_view_updater,'-update/2-fun-0-',6},
> {couch_btree,stream_kv_node2,7},
> {couch_btree,stream_kp_node,6},
> {couch_btree,fold,5},
> {couch_view_updater,update,2}]]},
> This problem occurs regardless of the functionality of the map and reduce
> functions, it seems to based on the time it takes to generate, or whatever
> causes the checkpoints to get written out.
> I did some investigation into the problem by adding alot of LOG_INFO
> statements throughout the code. I was able to determine the following:
>
> * the Erlang View process is being held on to by the view updater for the
> entire duration of the indexing,
> * however after the first checkpoint is hit and the progress is written
> out, a reduce call is made to the erlang view server, once this completes the
> view server is released back to the cache using ret_os_process.
> * when the next reduce cycle occurs the same erlang view server is
> returned by get_os_process but it is first sent a reset message which clears
> all the functions in the view servers state.
> * when the next map cycles starts the view updater uses the same handle to
> the erlang view server it had in the beginning. It assumes that the servers
> state is the same however it has been reset so there are no view functions in
> the view server. This causes the above error when it then attempts to write
> out the result of a view function which doesn't exist in the server.
> I was able to fix this problem by modifying line 139 of
> couch_view_updater.erl from this:
> {[], Group2, ViewEmptyKeyValues, []}
> to this:
> {[], Group2#group{query_server=nil}, ViewEmptyKeyValues, []}
> Which removes the view updater's handle to the erlang server proc, forcing it
> to get/create a new one for each map cycle and setting up the view functions
> within the server. I don't know if this is the right way to do it, or if it
> has any bad side-effects, but it does prevent the crash at least, and allow
> the indexing to complete correctly.
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