[BUG] fetch_size does not work when sending PPL request

[abbyhu2000]

What is the bug?
According to documentation, https://opensearch.org/docs/latest/search-plugins/sql/sql-ppl-api/#request-body-fields, fetch_size should control the size of the responses we got back for both PPL and SQL requests. However, currently when i send requests with fetch_size in the dev tool, only SQL works; PPL responses do not seem to respect the fetch_size param and still return the full size responses.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Go to dev tool
2. type

POST _plugins/_ppl/
{
  "fetch_size" : 1,
  "query" : "source = opensearch_dashboards_sample_data_flights",
}

3. Send the request
4. See responses return with full size, but not size 1

What is your host/environment?

• Version 2.18

Do you have any screenshots?

Screen.Recording.2025-02-07.at.3.00.06.PM.mov

Do you have any additional context?
Add any other context about the problem.