SAI-4731 : supporting feature flag in solr

[noblepaul]

sample code

WatchedClusterProperties wcp =
        ch.getCoreContainer().getZkController().getWatchedClusterProperties();
    wcp.watchProperty(
        "prop1",
        (k, v) -> {
         //do something
        });
    wcp.watchProperty(
        "prop2",
        (k, v) -> {
          // do something
        });
        

[hiteshk25]

@noblepaul looks like host level support is not there yet?

[noblepaul]

@hiteshk25

per node properties ar implemented

[hiteshk25]

What all way we can define this?

1. Can we differentiate between two components? (say, component-x, component-y)
2. Can we define prop for component-x (node-level, otherwise-all, just-for-all) ?

[noblepaul]

It's not per component, it's just a property per node. May be we can prefix a component name in the property key

[hiteshk25]

I think we need three cases here

1. One can define properties at component level. While registering watch take component-name, if same exists then through the exception.
2. Component will register default value, which we can update through ZK (or maybe later nice solr api)
   2.1. We can update component1-prop in ZK with node name, saying apply this value for that node. Then we should call listener for that component on that node only.

Side node, recently we introduced this behavior in prod, where we updated max-basic-queries limit on one solr-node. We watched that node for ~4/5 weeks and now we ready to update this limit on all the nodes. This solution require whole cluster restart, that's why we are looking for this feature in solr. Hope this will help.

[noblepaul]

for example , if there is a property component-a.property-x that component may watch that property explicitly at load time. if no other component has registered a watch on that property, then no callbacks are given to other components. Am I missing something?

[hiteshk25]

f there is a property component-a.property-x that component may watch that property explicitly at load time.

As long as component is registered, it should get callback. do you think it should register property as well?

[noblepaul]

there is no concept of a "component" is Solr. So, the system would not know whom to give a callback if it does not explicitly register for a callback

[hiteshk25]

It's just name if we need to use feature flag. watch("test1", listener)

[hiteshk25]

if prop is set for node1, then we need to invoke listener on that node only

[noblepaul]

yeah, that is what it does. You register the watcher from within a node and listeners are fired for the properties of that node only

[hiteshk25]

What will happens we update the property in ZK, will that cause listener-update-event on each node or all node?

[noblepaul]

what do you mean by each node and all node?

everyone who registered a listener should get a callback

[hiteshk25]

For example I want these property value for this node only

{
  component: "basiclimit", host:solr-1,property-x:value-y
} 

Then this should be invoked on host solr-1 only.

[noblepaul]

when the property is defined for solr-1 , you get a calback on solr-1 only.
It would look something like this. Inside a node, you can only watch properties of that node

{
  "watched-node-properties" :{
    "solr-1" : {
        "basiclimit.property-x":"value-y"
    }
  }
}

[hiteshk25]

Nice, let's give demo on this in Monday's sync. thanks!

[hiteshk25]

@noblepaul let's plan for updated demo on Monday's sync