Reindexing creates frivolous tasks (ES 2.3.3,. 2.4)

Elastic Stack Elasticsearch
1

I have noticed it multiple times that when I try to reindex any of my index (/_reindex), I see multiple tasks which all try to execute same reindexing operation. These tasks still persist even when the reindexing is essentially over.

I don't know what causes this behaviour and It adds load to my search rate.

2

Can you provide more details, like showing what these tasks are?

3

I've seen this mentioned a few times now but never been able to reproduce it and I've spent quite a bit of time on reindex. Most folks seem to have no trouble with reindex and, like I said, I can't make it happen either.

Is there any chance you could create a gist of curl 'localhost:9200/_tasks/?pretty&detailed=true&actions=*reindex when this happens again? Does it happen every time you reindex or just sometimes? Do you _update_by_query or _delete_by_query and, if you do, does this ever happen with them?