Couchbase 4.5 - increasing index storage

Hi We have a couchbase cluster with 3 data nodes and an index node and a single index on a bucket with 15 million items. The initial index storage size was 10GB. When 4 million items with max index size for each record 512 bytes, got added, the index storage size has increased to 43GB. The indexer logs say the index compaction is successful with message every day" Finished compacting index instance " but the storage size does not shrink. Any idea what could be the issue? The data compaction seems to be fine.

@naveen.dn Could you please share the complete cbcollect for us to analyse the issue?

What is the fragmentation ratio of the index after compaction? Can you also check what are your compaction settings(in UI->Settings)?