ElasticsSearch performnce consideration

Hi Everyone,

I am new to ElaticSearch and we have some projects to move some our existing Databases from SQL SERVER to ElaticSearch. We are going to use ElasticSearch service provided in AWS. We are planing to use two below features. Does below features reduce the performance? Is there any performance consideration for below features.

1- Cross Cluster Search,in order to put old data into slower instance.(we can not use UltraWarm)
2- Using union (union result set from different indexes in the same domain)

FYI the aws service is a fork of Elasticsearch and as such is not actual Elasticsearch. We are unable to provide support or recommendations if you use that service as they do not publish the changes they make to the product we develop and release.

This will not work with the aws service at all.

Elasticsearch SQL will not work with the aws service either.