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Allow for flatmap passthrough in the FieldWriter #86

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Allow for flatmap passthrough in the FieldWriter #86

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Commits on Sep 26, 2024

  1. Allow for dictionary encoded vector ingestion 

    Summary:
Allows for already encoded dictionaries to passthrough the writer as opposed to being decoded + deduped again.

Specifically, we want to allow for a "passthrough" without decoding when the schema indicates that we are ingesting an ArrayVector, but the array we find is a dictionaryVector with ArrayVector values. When this is the case, we will check to see if the dictionary is a valid run-length encoding (meaning, it likely has been deduped by upstream). The way in which the vector is written to storage does not change, we will still write the offsets and the ArrayVector elements. 

A caveat is that right now, `isDictionaryValidRunLengthEncoded` function doesn't actually verify that there is a duplicate. It's possible that a scenario exists in which a DictionaryVector was passed to the ArrayVector field writer, but the DictionaryVector has not been deduped, but its offsets still technically fulfill a run-length encoding (each offset is greater than or equal to the offset at index - 1).

Reviewed By: helfman

Differential Revision: D59863671
    @facebook-github-bot
    Kunal Kataria authored and facebook-github-bot committed Sep 26, 2024
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  2. Add callback functionality to Options/Context to capture visits to ge… 

    …tLocalDecodedVector

Summary:
As title, in order to verify passthrough code is being correctly called and the local decoded vector is NOT being accessed, we need a way to track visits to the decode function. On suggestion/idea by helfman, we've created a visit callback passed in via the writer options which allows us to track if the decode visit has been called from the writer code. 

I did verify that the callback is being called through some tests that I know _do_ use the decode functionality. I plan to add decode visit counters for those tests later but  that is out of scope for this diff for now

This decode visit functionality will be used in the flatmap passthrough functionality as well

Reviewed By: helfman

Differential Revision: D60241883
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    Kunal Kataria authored and facebook-github-bot committed Sep 26, 2024
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  3. Add caching support for dictionary encoded passthrough 

    Summary:
Allows for caching of the last element when a dictionary encoded array is given for passthrough.

This will bring us up to parity of local file encoding with the original arrayWithOffsets, as two consecutive datasets, either passed as unencoded array or already encoded dictionaryArray will now have the same output into the file.

Reviewed By: helfman

Differential Revision: D60413733
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    Kunal Kataria authored and facebook-github-bot committed Sep 26, 2024
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  4. Allow for flatmap passthrough in the FieldWriter 

    Summary:
As title, allows for ingestion of RowVector in the FlatMapFieldWriter. Takes each item in the row and writes its child vector based on the ranges provided.

Currently not handled:
- Encoded row vectors with flatmap schema
- What happens when there are subsequent writes that have a different set of keys from the original write

Reviewed By: helfman

Differential Revision: D61456412
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    Kunal Kataria authored and facebook-github-bot committed Sep 26, 2024
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