Aggregator Nodes, What is it?

I have seen Aggregator Nodes in a couple of scenarios but I dont have a clear picture about what are they and what are their responsibilities. Thanks

Aggregator Nodes represent the app servers that take results from other servers (cache, DBs or other app servers), aggregate the results, sort or filter the results depending upon the requirements, and then return a set of results to the user. In the architecture diagram, these servers are referred as “Aggregator Server”.


Let me try my best to explain this point.
Aggregation server job is gather all the results from all the DB shards for specific search(this search could be collecting all the latest tweets to generate the feeds or search for collect all recent tweets related to one user which happens when you visit other person page) Aggregate means collect together all the chunks from different shards and then bundle them into one result and give it back to the app server to give to the user as a result on their page.

Author correct please if I am wrong