Shard size not even for the same index

One of our index is relatively big and I just found its shards size are not even, see below.

Any idea what could have cause this?
Will it cause any perf issues and anything I can do?


Are you using custom document routing? Is the index using parent-child relationships?

Thanks for the hint @Christian_Dahlqvist

I didn't find any routing config in the mapping of the index. How can I check for parent-child relationships?

Btw, we deleted a lot of documents in this index recently. This unbalance happened after that.

Then it may be that the shards are in different stages of merging so a lot of the deleted documents may not have been m,erged out yet for some shards. You can manually run a forcemerge and see if that reduces the size but that can be I/O intensive.

Seems like forcemerge have worked, thanks @Christian_Dahlqvist