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https://issues.apache.org/jira/browse/PARQUET-1879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17146850#comment-17146850
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ASF GitHub Bot commented on PARQUET-1879:
-----------------------------------------
maccamlc commented on pull request #798:
URL: https://github.com/apache/parquet-mr/pull/798#issuecomment-650527774
@gszadovszky before this gets merged, I just wanted to clarify something
myself after looking more into the format spec, that might tidy this issue up
further.
* Is MAP_KEY_VALUE required to still be written as the Converted Type when
creating new files?
From what I could see from some older issues and the
[backwards-compatibility
rules](https://github.com/apache/parquet-format/blob/master/LogicalTypes.md#backward-compatibility-rules-1)
it seems to have always been an optional type, and also used incorrectly in
the past.
It appears that older versions of Parquet would be able to read the Map type
in the schema without MAP_KEY_VALUE.
If that is true, I would probably suggest pushing this [additional
commit](https://github.com/maccamlc/parquet-mr/commit/3f774d123997a4c63631185ca409550ca03b960d)
that I tested, onto this PR.
It would mean that any unexpected uses of LogicalType.MAP_KEY_VALUE would
result in UNKNOWN being written to the file. But it is removed from the
ConversionPatterns path, meaning that my case of this occuring when converting
an Avro schema is still fixed, and tested.
Let me know if believe this might be the preferred fix, or if what have
already done is better.
Thanks
Matt
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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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