[jira] Commented: (COUCHDB-855) New host manager

["Filipe Manana (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/COUCHDB-855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12984392#action_12984392 ] 

Filipe Manana commented on COUCHDB-855:
---------------------------------------

Sorry for this insanely late reply. I missed the introduction of this patch completely.

I totally disagree making this a gen_server. This can have a very serious impact on performance when thousands of parallel requests come in.

The reason is that for each received request, a synchronous call is made against the vhost gen_server:

https://github.com/apache/couchdb/blob/trunk/src/couchdb/couch_httpd.erl#L172

The call itself basically does string comparsions, splitting, proplists lookups etc. All is CPU bound:

https://github.com/apache/couchdb/blob/trunk/src/couchdb/couch_httpd_vhost.erl#L145

This means, that like couch_file, couch_db_updater and couch_server, this is a serialization point, seriously limiting the amount of parallelism we can offer.

Is there any reason to make this a gen_server? To me it seems like a simple function call with closure variables (to avoid doing the couch_config:get calls, re:split, couch_httpd:make_arity_2_fun calls, etc everytime the mochiweb loop is called)

Therefore, sorry to say, my vote is -1 solely by the fact it adds a bottleneck

> New host manager
> ----------------
>
>                 Key: COUCHDB-855
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-855
>             Project: CouchDB
>          Issue Type: Improvement
>    Affects Versions: 1.1
>            Reporter: Benoit Chesneau
>            Assignee: Benoit Chesneau
>             Fix For: 1.1
>
>         Attachments: 0001-New-vhost-manager.-allows-dynamic-add-of-vhosts-with.patch, 0001-Squashed-commit-of-the-following.patch
>
>
> New vhost manager. allows dynamic add of vhosts without restart, wildcard in vhost and specific functions in erlang by kind of domain. It also fix issue in etap test (160) .
> Find attached to this ticket the patch. It is also available in my github repo :
> http://github.com/benoitc/couchdb/commit/435c756cc6e687886cc7055302963f422cf0e161
> more details :
> This gen_server keep state of vhosts added to the ini and try to
> match the Host header (or forwarded) against rules built against
> vhost list. 
> Declaration of vhosts take place in the configuration file :
> [vhosts]
> example.com = /example
> *.example.com = /example
> The first line will rewrite the rquest to display the content of the
> example database. This rule works only if the Host header is
> 'example.com' and won't work for CNAMEs. Second rule on the other hand
> match all CNAMES to example db. So www.example.com or db.example.com
> will work.
> The wildcard ('*') should always be the last in the cnames:
>      "*.db.example.com = /"  will match all cname on top of db
> examples to the root of the machine. (for now no rewriting is
> possible).
> By default vhosts redirection is handle by the function
> couch_httpd_vhost:redirect_to_vhost, but you could pass per vhost a
> specific function :
>      "*.domain.com" = {Module, Func}"
> The function take the Mochiweb Request object and should return a new
> Mochiweb Request object.
> You could also change the default function to handle request by
> changing the setting `redirect_vhost_handler` in `httpd` section of
> the Ini:
>       [httpd]
>       redirect_vhost_handler = {Module, Fun}
> The function take 2 args : the mochiweb request object and the target
> path. 

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