Number of active threads for bulk thread_pool is equal to number of shards to which write is happening and not a single bulk request.
My understanding was that , active threads in thread_pool = number of concurrent bulk requests.
But seems this is equals to the number of shards to which write happens.
We have a bulk where we are writing to multiple indices in a single bulk request and it seems to exceed active threads + queue size and finally hitting rejection , even though we have only 1 bulk request in parallel.
Is my observation wrong or is Elasticsearch working like this ?