Azure Cosmos DB: 'Request rate is large' for simple count query

Question

I'm using Cosmos DB with the Mongo adapter, accessing via the Ruby mongo driver. Currently there are about 2.5M records in the db.

When querying the total amount of records, there's no problem whatsoever:

2.2.5 :011 > mongo_collection.count
D, [2017-11-24T11:52:39.796716 #9792] DEBUG -- : MONGODB | XXX.documents.azure.com:10255 | admin.count | STARTED | {"count"=>"xp_events", "query"=>{}}
D, [2017-11-24T11:52:39.954645 #9792] DEBUG -- : MONGODB | XXX.documents.azure.com:10255 | admin.count | SUCCEEDED | 0.15778699999999998s
 => 2565825

But when I try to count the amount of records found based on a simple where, I run into the Request rate is large error:

2.2.5 :014 > mongo_collection.find(some_field: 'some_value').count
D, [2017-11-24T11:56:11.926812 #9792] DEBUG -- : MONGODB | XXX.documents.azure.com:10255 | admin.count | STARTED | {"count"=>"some_table", "query"=>{"some_field"=>"some_value"}}
D, [2017-11-24T11:56:24.629659 #9792] DEBUG -- : MONGODB | XXX.documents.azure.com:10255 | admin.count | FAILED | Message: {"Errors":["Request rate is large"]}
ActivityId: 0000-0000-0000-000000000000, Request URI: /apps/XXX/services/XXX/partitions/XXX/replicas/XXX/, RequestStats: , SDK: Microsoft.Azure.Documents.Common/1.17.101.1 (16500), Message: {"Errors":["Request rate is large"]}

I understand how the error works, but I don't understand how such a query can max out the RU/s (set at max value 10,000), since the field I'm querying is supposed to be indexed (automatically).

Any advice would be greatly appreciated!

Answer 1

The error is by design, it means that an application is sending request to DocumentDB service at a rate that is higher than the 'reserved throughput' level for a collection tier.

The solution is that retry same request after some time. For more solutions check this article.