[Feature Request] Support of search pipelines in multisearch template

[ocuenca-coursera]

Is your feature request related to a problem? Please describe

I would be great if we can specify in a multisearch template request the search pipeline to execute as in msearch:

GET /_msearch
{ "index": "test"}
{ "query": { "match_all": {} }, "from": 0, "size": 10, "search_pipeline": "my_pipeline"}
{ "index": "test-1", "search_type": "dfs_query_then_fetch"}
{ "query": { "match_all": {} }, "search_pipeline": "my_pipeline1" }

Describe the solution you'd like

Would be the same idea as msearch, so a multisearch template request using search pipelines would look like this:

GET _msearch/template
{"index":"shakespeare"}
{"id":"line_search_template","params":{"text_entry":"All the world's a stage","limit":false,"size":2}, "search_pipeline": "my_pipeline2"}
{"index":"shakespeare"}
{"id":"play_search_template","params":{"play_name":"Henry IV"}, "search_pipeline": "my_pipeline1"}

Related component

Search:Query Capabilities

Describe alternatives you've considered

No response

Additional context

No response

[sandeshkr419]

[Search triage] @owaiskazi19 What do you think of this?

[ocuenca-coursera]

Thanks for taking a look @sandeshkr419. This is the thread where I started discussing if there was an existing solution for msearch template. @owaiskazi19 asked me to created this ticket

[owaiskazi19]

Yes, need to add this feature to support search pipeline in multi search template.

{"index":"my-nlp-index1"}
{"id":"search_template_1","params":{"play_name":"zoo","from":0,"size":1}, "search_pipeline": "my_pipeline2"}
{"index":"my-nlp-index1"}
{"id":"search_template_2","params":{"play_name":"hello","from":0,"size":1}, "search_pipeline": "my_pipeline2"}

{
    "error": {
        "root_cause": [
            {
                "type": "x_content_parse_exception",
                "reason": "[1:75] [search_template] unknown field [search_pipeline]"
            }
        ],
        "type": "x_content_parse_exception",
        "reason": "[1:75] [search_template] unknown field [search_pipeline]"
    },
    "status": 400
}

[owaiskazi19]

@ocuenca-coursera raised #18564 to add the support

[ocuenca-coursera]

nice! thanks @owaiskazi19, hopefully we can see it as part in the next release of OS!