Configuring mergeScheduler for SolrCloud

[6harat <bh...@gmail.com>]

Hi,

We have a solr cloud setup (tlog + pull - v8.2) which is currently showing
a large amount of CPU being used by Lucene Merge Thread pool which are
spawned by ConcurrentMergeScheduler. As a result of this, our writes have
considerably slowed down.

We were looking to fine tune that config basis this doc:
https://solr.apache.org/guide/8_2/indexconfig-in-solrconfig.html by
mentioning something like below inside the solrconfig.xml

<indexConfig>
    ...
    <mergeScheduler
class="org.apache.lucene.index.ConcurrentMergeScheduler">
      <int name="maxMergeCount">6</int>
      <int name="maxThreadCount">1</int>
    </mergeScheduler>
</indexConfig>

However, these configs are not getting honored (per the top output
captured) either on:
1. uploading the configs on zookeeper and reloading
2. uploading the configs on zookeeper and reloading and restarting the boxes
(we understand that these configs are only applicable for a leader")

Could you please point out what is the SOP to follow when changing configs
around: mergeScheduler, mergePolicyFactory or ramBufferSizeMB so that they
come into effect?

Also is there an API where the configs honored by the process are
displayed? I couldn't find these being reported by /admin/metrics API