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From "Adam Kocoloski (JIRA)" <j...@apache.org>
Subject [jira] Commented: (COUCHDB-901) refactor os process management
Date Thu, 21 Oct 2010 16:20:17 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12923498#action_12923498
] 

Adam Kocoloski commented on COUCHDB-901:
----------------------------------------

I added a feature to the couch_proc_manager in my github branch, a "soft limit" on the number
of OS processes.  In contrast to the code in trunk, which delays requests for OS processes,
couch_proc_manager will continue to spawn new processes, but it will only reuse the ones that
are returned if the number of active processes is below the soft limit.

I can see the benefit to a hard limit, but in general I feel pretty uneasy about blocking
short requests for an arbitrary amount of time.  The view updaters in particular will hold
onto an OS process for a very long time.  In my opinion a hard limit is probably most useful
to protect against malicious intent.

> 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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