"add-field" completes in minutes and sends replicas into full recovery

[S G]

Hi,

I have a Solr 6.5.1 cluster with a collection spawning 30 VMs.

I see that commands like the below "add-field" command complete in minutes
and send replicas into full recovery:

curl -X POST -H 'Content-type:application/json' --data-binary
'{"add-field":{"name":"some_new_field","type":"string","indexed":true,"stored":true,"required":false
}}' http://my-solr-host:8983/solr/my_collection/schema

{
  "responseHeader":{
    "status":0,
    "QTime":239578}
}


Any idea why that might be so?

We are not stopping the read/write traffic to Solr when adding fields like
the above.

Thanks
SG