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https://issues.apache.org/jira/browse/PARQUET-1936?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17232503#comment-17232503
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Micah Kornfield commented on PARQUET-1936:
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[~Ruta Dhaneshwar] sure, do you maybe want to make a PR to clarify?
> WriteBatchSpaced writes incorrect value for parquet when input contains NULL
> list
> ---------------------------------------------------------------------------------
>
> Key: PARQUET-1936
> URL: https://issues.apache.org/jira/browse/PARQUET-1936
> Project: Parquet
> Issue Type: Bug
> Components: parquet-cpp
> Reporter: Ruta Dhaneshwar
> Priority: Major
> Attachments: NULL list 1.png, NULL list 2.png, NULL list 3.png, NULL
> list 4.png, schema.png
>
>
> When trying to write a column of parquet lists, if there is a NULL list,
> WriteBatchSpaced will either throw an error (case 1 below) or incorrectly
> write the last value in the last list as the first value from the first list
> (case 2 below).
> *!schema.png|width=235,height=106!*
> *CASE 1*
> Data (3 lists):
> [
> "one"
> ]
> null
> [
> "two"
> ]
>
> Parameters to
> TypedColumnWriter<PhysicalType<parquet::Type::BYTE_ARRAY>>::WriteBatchSpaced:
> # num_values: 3
> # def_levels: [3, 0, 3]
> # rep_levels: [0, 0, 0]
> # valid_bits: 0x05 (bit representation 101)
> # valid_bits_offset: 0
> # values: ["one", nullptr, "two"]
> When I use WriteBatchSpaced(num_values, def_levels, rep_levels, valid_bits,
> valid_bits_offset, values), I get an error when running
> [parquet-tools|https://github.com/apache/parquet-mr/tree/master/parquet-tools]
> on the outputted parquet file:
> !NULL list 1.png|width=332,height=52!
> !NULL list 2.png|width=757,height=249!
> Additionally, if I add another list into the data that I write, then the last
> element of that additional list is incorrectly written as the first element
> of the first list. See below.
>
> *CASE 2*
> Data (4 lists):
> [
> "one"
> ]
> null
> [
> "two"
> ]
> [
> "three",
> "four"
> ]
>
> Parameters to
> TypedColumnWriter<PhysicalType<parquet::Type::BYTE_ARRAY>>::WriteBatchSpaced:
> # num_values: 5
> # def_levels: [3, 0, 3, 3, 3]
> # rep_levels: [0, 0, 0, 0, 1]
> # valid_bits: 0x29 (bit representation 11101)
> # valid_bits_offset: 0
> # values: ["one", nullptr, "two", "three", "four"]
> Outputted Parquet File:
> !NULL list 3.png|width=72,height=145!
> !NULL list 4.png|width=237,height=76!
>
> Here we see that the "four" in the last list actually shows up as "one".
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