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https://issues.apache.org/jira/browse/COUCHDB-901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12916222#action_12916222
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Paul Joseph Davis commented on COUCHDB-901:
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Its not a full switch to emonk, just a refactor to allow supporting emonk as
well as some other bits to make the various server process handling less funky.
The other major thing I did was to split couch_query_servers into two sets of
modules. couch_view_server for map/reduce views, and couch_app_server for
everything else. Each set of modules has an API module and a set of
implementation modules. For instance:
couch_view_server.erl
couch_view_server_emonk.erl
couch_view_server_erlang.erl
couch_view_server_os.erl
All calls from external code go to couch_view_server that returns an opaque
term that ends up calling out to the actual implementation module.
The main things missing from my code are finishing the implementations for the
non-emonk app servers and some refactoring in a few places so that things like
couch_view_server_os.erl and couch_app_server_os.erl share the same code for
managing OS level processes. The couch_proc_manager.erl in Adam's patch looks
like exactly what I need for this so that'll help.
> refactor os process management
> ------------------------------
>
> Key: COUCHDB-901
> URL: https://issues.apache.org/jira/browse/COUCHDB-901
> Project: CouchDB
> Issue Type: Improvement
> Components: Database Core
> Affects Versions: 1.0.1
> Reporter: Adam Kocoloski
> Fix For: 1.1
>
>
> Wanted to make sure this doesn't get forgotten in the planning for 1.1. Paul
> Davis and I independently refactored couch_query_servers. Paul's work is
> much more comprehensive and includes a switch to emonk:
> http://github.com/davisp/couchdb/tree/emonk
> The work I did is here
> http://github.com/kocolosk/couchdb/tree/COUCHDB-901
> One feature not included in that branch is the ability to limit the number of
> OS processes. Should be simple to add if my work ends up being merged. I
> did the refactor because I was having problems with couch_query_servers
> "forgetting" about OS processes in BigCouch. One of the ets tables held by
> couch_query_servers would list thousands of processes (and in fact there were
> thousands of spawned couchjs), but another table would claim that only two
> were running. After digging through the code a while I became frustrated
> with all of the tracking of multiple ets tables and rewrote a server that
> used only one table. Other changes include
> * ability to reuse an OS process when the client that requested it dies.
> * better behavior under config changes - doesn't kill all query servers when
> [query_servers] or [native_query_servers] block changes
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