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https://issues.apache.org/jira/browse/IMPALA-10798?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17762221#comment-17762221
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ASF subversion and git services commented on IMPALA-10798:
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Commit 2f06a7b052cc95afcf4b0485cbc4028de33942e8 in impala's branch
refs/heads/master from Eyizoha
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=2f06a7b05 ]
IMPALA-10798: Initial support for reading JSON files
Prototype of HdfsJsonScanner implemented based on rapidjson, which
supports scanning data from splitting json files.
The scanning of JSON data is mainly completed by two parts working
together. The first part is the JsonParser responsible for parsing the
JSON object, which is implemented based on the SAX-style API of
rapidjson. It reads data from the char stream, parses it, and calls the
corresponding callback function when encountering the corresponding JSON
element. See the comments of the JsonParser class for more details.
The other part is the HdfsJsonScanner, which inherits from HdfsScanner
and provides callback functions for the JsonParser. The callback
functions are responsible for providing data buffers to the Parser and
converting and materializing the Parser's parsing results into RowBatch.
It should be noted that the parser returns numeric values as strings to
the scanner. The scanner uses the TextConverter class to convert the
strings to the desired types, similar to how the HdfsTextScanner works.
This is an advantage compared to using number value provided by
rapidjson directly, as it eliminates concerns about inconsistencies in
converting decimals (e.g. losing precision).
Added a startup flag, enable_json_scanner, to be able to disable this
feature if we hit critical bugs in production.
Limitations
- Multiline json objects are not fully supported yet. It is ok when
each file has only one scan range. However, when a file has multiple
scan ranges, there is a small probability of incomplete scanning of
multiline JSON objects that span ScanRange boundaries (in such cases,
parsing errors may be reported). For more details, please refer to
the comments in the 'multiline_json.test'.
- Compressed JSON files are not supported yet.
- Complex types are not supported yet.
Tests
- Most of the existing end-to-end tests can run on JSON format.
- Add TestQueriesJsonTables in test_queries.py for testing multiline,
malformed, and overflow in JSON.
Change-Id: I31309cb8f2d04722a0508b3f9b8f1532ad49a569
Reviewed-on: http://gerrit.cloudera.org:8080/19699
Reviewed-by: Quanlong Huang <huangquanl...@gmail.com>
Tested-by: Impala Public Jenkins <impala-public-jenk...@cloudera.com>
> Prototype a simple JSON File reader
> -----------------------------------
>
> Key: IMPALA-10798
> URL: https://issues.apache.org/jira/browse/IMPALA-10798
> Project: IMPALA
> Issue Type: Sub-task
> Reporter: Shikha Asrani
> Assignee: Ye Zihao
> Priority: Major
>
> This prototype involves ,
> * Implementing front-end support for 'Select' from a table "stored as
> JSONFILE".
> * A JSON file scanner, using Arrow library to read the JSON file with
> primitive data types and is expandable for further complex types and
> optimizations.
>
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