[Feature Request] Improve performance of sort by _id about opensearch

[dvjyothsna]

@msfroh

[dvjyothsna]

@saratvemulapalli

[msfroh]

@dvjyothsna -- can you please clarify what the problem is that needs solving?

From what I can see, we do support sorting, but we output this deprecation message:

OpenSearch/server/src/main/java/org/opensearch/index/mapper/IdFieldMapper.java

Line 84 in 09bacee

"Loading the fielddata on the _id field is deprecated and will be removed in future versions. "

One of the workarounds is to copy the _id field into a doc value field. But it doesn't work for our usecase since ther user trying to paginate has readonly access.

The efficient way to support sorting on a field is to enable doc values on that field. I don't think we would ever enable doc values on the _id field by default, since it would increase the size of the index for all users, whether they want to sort on _id or not. We could add a mapping flag to store a doc value for the _id field, but that wouldn't help your readonly user (and would be functionally equivalent to copying the _id field into another field with doc values enabled).