Alias creation slow!

Hi,
We are using Elasticsearch for our search application. currently we have 3 master nodes and 5 data nodes in our cluster with 160 indices with 5 shards each and replica of 2.

Currently we have 20k users. We will create alias for each user with alias name as user id. As the number of alias gets increased, time to add alias also getting increased consistently. Now alias creation takes upto 10 secs for most of the time.

PS : found similar case here

Is there any workaround for this.

Any help in resolving this issue will be appreciated .

Thanks in advance

Ranjith Venkatesan