+1 on Jun's suggestion. On 2/10/14 2:01 PM, "Jun Rao" <jun...@gmail.com> wrote:
>I actually prefer to see those at INFO level. The reason is that the >config >system in an application can be complex. Some configs can be overridden in >different layers and it may not be easy to determine what the final >binding >value is. The logging in Kafka will serve as the source of truth. > >For reference, ZK client logs all overridden values during initialization. >It's a one time thing during starting up, so shouldn't add much noise. >It's >very useful for debugging subtle config issues. > >Exposing final configs programmatically is potentially useful. If we don't >want to log overridden values out of box, an app can achieve the same >thing >using the programming api. The only missing thing is that we won't know >those unused property keys, which is probably less important than seeing >the overridden values. > >Thanks, > >Jun > > >On Mon, Feb 10, 2014 at 10:15 AM, Jay Kreps <jay.kr...@gmail.com> wrote: > >> Hey Jun, >> >> I think that is reasonable but would object to having it be debug >>logging? >> I think logging out a bunch of noise during normal operation in a client >> library is pretty ugly. Also, is there value in exposing the final >>configs >> programmatically? >> >> -Jay >> >> >> >> On Sun, Feb 9, 2014 at 9:23 PM, Jun Rao <jun...@gmail.com> wrote: >> >> > +1 on the new config. Just one comment. Currently, when initiating a >> config >> > (e.g. ProducerConfig), we log those overridden property values and >>unused >> > property keys (likely due to mis-spelling). This has been very useful >>for >> > config verification. It would be good to add similar support in the >>new >> > config. >> > >> > Thanks, >> > >> > Jun >> > >> > >> > On Tue, Feb 4, 2014 at 9:34 AM, Jay Kreps <jay.kr...@gmail.com> wrote: >> > >> > > We touched on this a bit in previous discussions, but I wanted to >>draw >> > out >> > > the approach to config specifically as an item of discussion. >> > > >> > > The new producer and consumer use a similar key-value config >>approach >> as >> > > the existing scala clients but have different implementation code to >> help >> > > define these configs. The plan is to use the same approach on the >> server, >> > > once the new clients are complete; so if we agree on this approach >>it >> > will >> > > be the new default across the board. >> > > >> > > Let me split this into two parts. First I will try to motivate the >>use >> of >> > > key-value pairs as a configuration api. Then let me discuss the >> mechanics >> > > of specifying and parsing these. If we agree on the public api then >>the >> > > public api then the implementation details are interesting as this >>will >> > be >> > > shared across producer, consumer, and broker and potentially some >> tools; >> > > but if we disagree about the api then there is no point in >>discussing >> the >> > > implementation. >> > > >> > > Let me explain the rationale for this. In a sense a key-value map of >> > > configs is the worst possible API to the programmer using the >>clients. >> > Let >> > > me contrast the pros and cons versus a POJO and motivate why I >>think it >> > is >> > > still superior overall. >> > > >> > > Pro: An application can externalize the configuration of its kafka >> > clients >> > > into its own configuration. Whatever config management system the >> client >> > > application is using will likely support key-value pairs, so the >>client >> > > should be able to directly pull whatever configurations are present >>and >> > use >> > > them in its client. This means that any configuration the client >> supports >> > > can be added to any application at runtime. With the pojo approach >>the >> > > client application has to expose each pojo getter as some config >> > parameter. >> > > The result of many applications doing this is that the config is >> > different >> > > for each and it is very hard to have a standard client config shared >> > > across. Moving config into config files allows the usual tooling >> (version >> > > control, review, audit, config deployments separate from code >>pushes, >> > > etc.). >> > > >> > > Pro: Backwards and forwards compatibility. Provided we stick to our >> java >> > > api many internals can evolve and expose new configs. The >>application >> can >> > > support both the new and old client by just specifying a config that >> will >> > > be unused in the older version (and of course the reverse--we can >> remove >> > > obsolete configs). >> > > >> > > Pro: We can use a similar mechanism for both the client and the >>server. >> > > Since most people run the server as a stand-alone process it needs a >> > config >> > > file. >> > > >> > > Pro: Systems like Samza that need to ship configs across the network >> can >> > > easily do so as configs have a natural serialized form. This can be >> done >> > > with pojos using java serialization but it is ugly and has bizare >> failure >> > > cases. >> > > >> > > Con: The IDE gives nice auto-completion for pojos. >> > > >> > > Con: There are some advantages to javadoc as a documentation >>mechanism >> > for >> > > java people. >> > > >> > > Basically to me this is about operability versus niceness of api >>and I >> > > think operability is more important. >> > > >> > > Let me now give some details of the config support classes in >> > > kafka.common.config and how they are intended to be used. >> > > >> > > The goal of this code is the following: >> > > 1. Make specifying configs, their expected type (string, numbers, >> lists, >> > > etc) simple and declarative >> > > 2. Allow for validating simple checks (numeric range checks, etc) >> > > 3. Make the config "self-documenting". I.e. we should be able to >>write >> > code >> > > that generates the configuration documentation off the config def. >> > > 4. Specify default values. >> > > 5. Track which configs actually get used. >> > > 6. Make it easy to get config values. >> > > >> > > There are two classes there: ConfigDef and AbstractConfig. ConfigDef >> > > defines the specification of the accepted configurations and >> > AbstractConfig >> > > is a helper class for implementing the configuration class. The >> > difference >> > > is kind of like the difference between a "class" and an "object": >> > ConfigDef >> > > is for specifying the configurations that are accepted, >>AbstractConfig >> is >> > > the base class for an instance of these configs. >> > > >> > > You can see this in action here: >> > > >> > > >> > >> >>https://git-wip-us.apache.org/repos/asf?p=kafka.git;a=blob_plain;f=client >>s/src/main/java/kafka/clients/producer/ProducerConfig.java;hb=HEAD >> > > >> > > (Ignore the static config names in there for now...I'm not actually >> sure >> > > that is the best approach). >> > > >> > > So the way this works is that the config specification is defined >>as: >> > > >> > > config = new ConfigDef().define("bootstrap.brokers", >>Type.LIST, >> > > "documentation") >> > > >> > > .define("metadata.timeout.ms", >> > Type.LONG, >> > > 60 * 1000, atLeast(0), "documentation") >> > > .define("max.partition.size", >>Type.INT, >> > > 16384, atLeast(0), "documentation") >> > > >> > > >> > > This is used in a ProducerConfig class which extends AbstractConfig >>to >> > get >> > > access to some helper methods as well as the logic for tracking >>which >> > > configs get accessed. >> > > >> > > Currently I have included static String variables for each of the >> config >> > > names in that class. However I actually think that is not very >>helpful >> as >> > > the javadoc for them doesn't give the constant value and requires >> > > duplicating the documentation. To understand this point look at the >> > javadoc >> > > and note that the doc on the string is not the same as what we >>define >> in >> > > the ConfigDef. We could just have the javadoc for the config string >>be >> > the >> > > source of truth but it is actually pretty inconvient for that as it >> > doesn't >> > > show you the value of the constant, just the variable name (unless >>you >> > > discover how to unhide it). That is fine for the clients, but for >>the >> > > server would be very weird especially for non-java people. We could >> > attempt >> > > to duplicate documentation between the javadoc and the ConfigDef but >> > given >> > > our struggle to get well-documented config in a single place this >>seems >> > > unwise. >> > > >> > > So I recommend we have a single source for documentation of these >>and >> > that >> > > that source be the website documentation on configuration that >>covers >> > > clients and server and that that be generated off the config defs. >>The >> > > javadoc on KafkaProducer will link to this table so it should be >>quite >> > > convenient to discover. This makes things a little more typo prone, >>but >> > > that should be easily caught by the key detection. This will also >>make >> it >> > > possible for us to retire configs in the future without causing >>compile >> > > failures and add configs without having use of them break backwards >> > > compatibility. This is useful during upgrades where you want to be >> > > compatible with the old and new version so you can roll forwards and >> > > backwards. >> > > >> > > -Jay >> > > >> > >>
