sampler + type detection = bff

[clintropolis]

Description

This PR improves the response from /druid/indexer/v1/sampler to now include dimensions and segmentSchema which are a list of dimension schemas and a RowSignature for the set of rows sampled.

Building on top of #13653, when the sampler spec included with

...
    "dimensionsSpec": {
        "dimensions": [],
        "useSchemaDiscovery": true
...
      },
...

it allows an application (such as the web-console data loader) to get typing information about the sampled data in schemaless mode.

For example, given a kafka stream

the new sampler response contains something like:

{
    "numRowsRead":4,
    "numRowsIndexed":4,
    "logicalDimensions":[
        {"type":"string","name":"time","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"long","name":"some_long","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":false},
        {"type":"double","name":"some_double","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":false},
        {"type":"string","name":"some_string","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_variant","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_nested","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true}
    ],
    "physicalDimensions":[
        {"type":"json","name":"time","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_long","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_double","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_string","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_variant","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_nested","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true}
    ],
    "logicalSegmentSchema":[
        {"name":"__time","type":"LONG"},
        {"name":"time","type":"STRING"},
        {"name":"some_long","type":"LONG"},
        {"name":"some_double","type":"DOUBLE"},
        {"name":"some_string","type":"STRING"},
        {"name":"some_variant","type":"COMPLEX<json>"},
        {"name":"some_nested","type":"COMPLEX<json>"}
    ],
    "data":[...]
}

which evolves as we proceed through data loader steps:

{
    "numRowsRead":4,
    "numRowsIndexed":4,
    "logicalDimensions":[
        {"type":"long","name":"some_long","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":false},
        {"type":"double","name":"some_double","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":false},
        {"type":"string","name":"some_string","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_variant","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_nested","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true}
    ],
    "physicalDimensions":[
        {"type":"json","name":"some_long","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_double","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_string","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_variant","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true},
        {"type":"json","name":"some_nested","multiValueHandling":"SORTED_ARRAY","createBitmapIndex":true}
    ],
    "logicalSegmentSchema":[
        {"name":"__time","type":"LONG"},
        {"name":"some_long","type":"LONG"},
        {"name":"some_double","type":"DOUBLE"},
        {"name":"some_string","type":"STRING"},
        {"name":"some_variant","type":"COMPLEX<json>"},
        {"name":"some_nested","type":"COMPLEX<json>"}
    ],
    "data":[...]
}

After this PR we can update the web-console to take advantage of this new information, which would help simplify some things.

Release note

/druid/indexer/v1/sampler has been improved to now include logicalDimension, physicalDimension and logicalSegmentSchema which are a list of the most restrictive typed dimension schemas, the list of dimension schemas actually used to sample the data, and full resulting segment schema for the set of rows sampled respectively.

---

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[abhishekagarwal87]

Nice. are you also going to change docs?

[imply-cheddar]

I had expected the first set of output to have one sub-section that is the specific detected type (maybe the "segmentSchema" chunk?) and another output that was the actual physical "indexer type" (maybe the "dimension" chunk?). For something that is fully running with the auto-detection, I would expect the physical "indexer type" one to just be json typed all the way down as that is what was used to ingest it.

[clintropolis]

Nice. are you also going to change docs?

I was holding off on docs since I'm not quite sure this has solidified yet, but looking closer I'm not sure we have any docs on the sampler API at all, so I think I'd definitely rather not do it in this PR.