[GitHub] [couchdb] iilyak commented on issue #2662: Use `couch_rate` application for `couch_view`

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iilyak commented on issue #2662: Use `couch_rate` application for `couch_view`
URL: https://github.com/apache/couchdb/pull/2662#issuecomment-599598983
 
 
   > // Creates new rate limiter. Internally couch_rate would look at the config to get the rate_limiter module for couch_views as well as know it needs to use the ets one for it.
   `RateLimiterState = couch_rate:new(couch_views);`
   
   Are you proposing to make `couch_rate` to be aware of `config` application? I.e. you would pass the name of the config section `to couch_rate:new`. Something like:
   ```
   -module(couch_rate).
   
   new(ConfigSection) ->
        ModuleStr = config:get(ConfigSection, "rate_limiter", "couch_rate_limiter"),
        Options = case config:get(ConfigSection, "rate_limiter_opts", undefined) of
           undefined -> DefaultConfig;
           OptionsStr -> couch_rate_config:from_str(OptionsStr)
        end,
   ```
   How we would define default options for the case when rate_limiter_opts key is not configured? Would we disable rate_limiter?
   
   > When I look at the couch_views_indexer file it feels to me like the couch_views_indexer is having to understand too much of how the rate_limiter works.
   
   Are you worried about configuration aspect or API aspect here? Because we would have to use `new/success/failure/budget/in` (and either delay or wait) APIs anyway for the proposed algorithm to work. We could rename some of the function but they are needed. The `new` and `budget` wouldn't be sufficient.
   
   > The other thing is how would we turn the rate_limiter off? If someone is happy for all views to go full speed even if it affects other views how would we do that?
   
   You would set `budget` to `100` (this is a replacement parameter for `couch_views.change_limit` which currently defaults to `100`) and `target` to `5000` which is a FDB transaction timeout (or 6000 to be safe).

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