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Posted to commits@pinot.apache.org by GitBox <gi...@apache.org> on 2022/07/21 07:14:26 UTC
[GitHub] [pinot] gortiz opened a new issue, #9081: Ingest parquet: Change behavior when ingesting columns of invalid type
gortiz opened a new issue, #9081:
URL: https://github.com/apache/pinot/issues/9081
TL;DR: There is an inconsistency in Pinot when a table defines a column as a string but it is populated reading a parquet file whose column type is binary without the string annotation.
Introduction:
I'm trying to improve the current Pinot implementation of [ClickHouse/ClickBench](https://github.com/ClickHouse/ClickBench). In that benchmark the input data can be read from csvs, tsvs, json or parquet files. As usual, Pinot requires to split the data before ingesting. The current implementation reads it from a tsv, but it seems easier and faster to read it from parquet. Even better, ClickHouse already provides a version that is already split. But the metadata on the parquet file is not correct. String columns are marked as binaries without [String annotation](https://github.com/apache/parquet-format/blob/master/LogicalTypes.md#string).
The problem:
When Pinot tries to populate a String column from a parquet file, it reads the values from the parquet files, applies some conversions that return an Object and applies a stringify conversion to that Object (like calling `Object.toString`). But the value that is read from parquet is depends on the metadata associated with the parquet column. In parquet String columns are Binary columns with an annotation that marks them as a String. Other annotations can be applied to mark the column as an enum or UUID.
Pinot uses these annotations to decide how to read the value, without knowing the type of the Pinot column where the data will be stored. The code that does that is [here](https://github.com/apache/pinot/blob/6903856d399b4d7b09548a75a888382e1659e9e3/pinot-plugins/pinot-input-format/pinot-parquet/src/main/java/org/apache/pinot/plugin/inputformat/parquet/ParquetNativeRecordExtractor.java). In case the binary column is not annotated with the String annotation, it is read as a binary (or some other variants, which are not important here). When the value is read as a String, the Java type will be String. When the value is read as a binary, the Java type will be `byte[]`.
Once the value is extracted, Pinot stringifies the value before storing it. If the parquet column was annotated with String, the value read is a String and therefore the conversion is a noop. But if the value wasn't annotated with String, the value read is a byte[] and therefore the conversion returns a description of the bytes. I didn't find where the conversion is applied, but the result is that Pinot stores a String that is not the bytes read as UTF-8.
This is problematic because there is no clear indicator that the import is going to change the data and there is no failure. The user may think that everything is ok and after ingesting terabytes of data he/she may discover that the data stored is not the same that the one he/she wanted to store.
It is possible that this problem is replicated with other input formats and other column types.
Proposed solutions:
1. Add some checks to the import process that verifies that the extracted Java types matches with the expected column type. In this case this would produce a failfast error that should be clear to the user, which can take proper adjustments (like adding the corresponding annotation to parquet).
2. Add a property to `org.apache.pinot.plugin.inputformat.parquet.ParquetRecordReaderConfig` that let the user to customize how columns should be read.
IMO the error should be mandatory and the ability to _cast_ the columns should be optional.
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[GitHub] [pinot] walterddr commented on issue #9081: Ingest parquet: Change behavior when ingesting columns of invalid type
Posted by GitBox <gi...@apache.org>.
walterddr commented on issue #9081:
URL: https://github.com/apache/pinot/issues/9081#issuecomment-1191540675
@siddharthteotia @Jackie-Jiang @yupeng9 ^
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[GitHub] [pinot] Jackie-Jiang commented on issue #9081: Ingest parquet: Change behavior when ingesting columns of invalid type
Posted by GitBox <gi...@apache.org>.
Jackie-Jiang commented on issue #9081:
URL: https://github.com/apache/pinot/issues/9081#issuecomment-1191852715
Currently we convert `BYTES` to hex-encoded string if the storage type is string. This is done in `PinotDataType.BYTES.toString()`.
We may consider adding a flag to only allow number conversion (IMO conversion between different number types should be allowed)
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[GitHub] [pinot] gortiz closed issue #9081: Ingest parquet: Change behavior when ingesting columns of invalid type
Posted by "gortiz (via GitHub)" <gi...@apache.org>.
gortiz closed issue #9081: Ingest parquet: Change behavior when ingesting columns of invalid type
URL: https://github.com/apache/pinot/issues/9081
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