SOLR-17240: Fix Http2SolrClient maxConnectionsPerDestination usage

[HoustonPutman]

https://issues.apache.org/jira/browse/SOLR-17240

[markrmiller]

Oh wow, I thought it was just defaulting to 4 and you couldn't necessarily change that everywhere in internal use because I saw the setMaxConnectionsPerHost in the builder. I didn't realize that that is a complete noop for http2 mode. That seems like a silly choice in any scenario.

[magibney]

javadoc should be updated on HttpSolrClientBuilderBase.withMaxConnectionsPerHost(int), explaining the new difference between how this is handled for http1 vs http2.

I wonder, to approximate similar high-level behavior for http1 vs http2, could the http2 client, under the hood, interpret this setting as ((maxConnectionsPerDest - 1) / 300) + 1, or something? I don't like having that 300 constant hardcoded there, as presumably the multiplexing factor in jetty could change ... but idk, something along those lines might address Sanjay's concern.

[HoustonPutman]

Ok I've updated the docs, and used the maxConcurrentPushedStreams to get the multiplexing factor.

This should probably be good to go?

[markrmiller]

under the hood, interpret this setting as ((maxConnectionsPerDest - 1) / 300) + 1, or something? I don't like having that 300 constant hardcoded there, as presumably the multiplexing factor in jetty could change ... but idk, something along those lines might address Sanjay's concern.

I don't think you want to do that, this should do what it says and set the max connections and not relate to multiplexing. Multiplexing should be it's own setter if you want it be configurable but trying to tie the two together really wouldn't do the user any favors.

[HoustonPutman]

under the hood, interpret this setting as ((maxConnectionsPerDest - 1) / 300) + 1, or something? I don't like having that 300 constant hardcoded there, as presumably the multiplexing factor in jetty could change ... but idk, something along those lines might address Sanjay's concern.

I don't think you want to do that, this should do what it says and set the max connections and not relate to multiplexing. Multiplexing should be it's own setter if you want it be configurable but trying to tie the two together really wouldn't do the user any favors.

Fair point mark. I'll make these things independent, add documentation, and make the defaults across solr make sense for both http1 and http2.