ASF GitHub Bot commented on PARQUET-1879:

maccamlc commented on pull request #798:
URL: https://github.com/apache/parquet-mr/pull/798#issuecomment-651009716

   > @maccamlc,
   > The main problem I think is that the spec does not say anything about how 
the thrift objects shall be used. The specification is about the semantics of 
the schema and it is described using the parquet schema _language_. But, in the 
file there is no such _language_, we only have [thrift 
   > When the specification says something about the _logical types_ (e.g. 
`MAP`) it does not say anything about which thrift structure should be used 
(the converted type 
 or the logical type 
   > We added the new logical type structures in the thrift to support enhanced 
ways to specify _logical types_ (e.g. 
 The idea for backward compatibility was to write the old converted types 
wherever it make sense (the semantics of the actual _logical type_ is the same 
as was before) along with the new logical type structures. So, related to 
`MAP_KEY_VALUE`, I think, we shall write it at the correct place if it was 
written before (prior to `1.11.0`) and it helps for other readers but do not 
expect it to be there.
   > Cheers,
   > Gabor
   Sounds good @gszadovszky . Thanks for some clarification.
   Therefore, depending on any other comments from other reviewers, it seems 
this PR is still ready to merge as-is :)

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> Apache Arrow can not read a Parquet File written with Parqet-Avro 1.11.0 with 
> a Map field
> -----------------------------------------------------------------------------------------
>                 Key: PARQUET-1879
>                 URL: https://issues.apache.org/jira/browse/PARQUET-1879
>             Project: Parquet
>          Issue Type: Bug
>          Components: parquet-avro, parquet-format
>    Affects Versions: 1.11.0
>            Reporter: Matthew McMahon
>            Priority: Critical
> From my 
> [StackOverflow|https://stackoverflow.com/questions/62504757/issue-with-loading-parquet-data-into-snowflake-cloud-database-when-written-with]
>  in relation to an issue I'm having with getting Snowflake (Cloud DB) to load 
> Parquet files written with version 1.11.0
> ----
> The problem only appears when using a map schema field in the Avro schema. 
> For example:
> {code:java}
>     {
>       "name": "FeatureAmounts",
>       "type": {
>         "type": "map",
>         "values": "records.MoneyDecimal"
>       }
>     }
> {code}
> When using Parquet-Avro to write the file, a bad Parquet schema ends up with, 
> for example
> {code:java}
> message record.ResponseRecord {
>   required binary GroupId (STRING);
>   required int64 EntryTime (TIMESTAMP(MILLIS,true));
>   required int64 HandlingDuration;
>   required binary Id (STRING);
>   optional binary ResponseId (STRING);
>   required binary RequestId (STRING);
>   optional fixed_len_byte_array(12) CostInUSD (DECIMAL(28,15));
>   required group FeatureAmounts (MAP) {
>     repeated group map (MAP_KEY_VALUE) {
>       required binary key (STRING);
>       required fixed_len_byte_array(12) value (DECIMAL(28,15));
>     }
>   }
> }
> {code}
> From the great answer to my StackOverflow, it seems the issue is that the 
> 1.11.0 Parquet-Avro is still using the legacy MAP_KEY_VALUE converted type, 
> that has no logical type equivalent. From the comment on 
> [LogicalTypeAnnotation|https://github.com/apache/parquet-mr/blob/84c954d8a4feef2d9bdad7a236a7268ef71a1c25/parquet-column/src/main/java/org/apache/parquet/schema/LogicalTypeAnnotation.java#L904]
> {code:java}
> // This logical type annotation is implemented to support backward 
> compatibility with ConvertedType.
>   // The new logical type representation in parquet-format doesn't have any 
> key-value type,
>   // thus this annotation is mapped to UNKNOWN. This type shouldn't be used.
> {code}
> However, it seems this is being written with the latest 1.11.0, which then 
> causes Apache Arrow to fail with
> {code:java}
> Logical type Null can not be applied to group node
> {code}
> As it appears that 
> [Arrow|https://github.com/apache/arrow/blob/master/cpp/src/parquet/types.cc#L629-L632]
>  only looks for the new logical type of Map or List, therefore this causes an 
> error.
> I have seen in Parquet Formats that 
> [LogicalTypes|https://github.com/apache/parquet-format/blob/master/LogicalTypes.md]
>  should be something like
> {code:java}
> // Map<String, Integer>
> required group my_map (MAP) {
>   repeated group key_value {
>     required binary key (UTF8);
>     optional int32 value;
>   }
> }
> {code}
> Is this on the correct path?

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