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https://issues.apache.org/jira/browse/DRILL-6953?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16985910#comment-16985910
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ASF GitHub Bot commented on DRILL-6953:
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arina-ielchiieva commented on issue #1913: DRILL-6953: EVF-based version of the
JSON reader
URL: https://github.com/apache/drill/pull/1913#issuecomment-560298026
@vvysotskyi bested the review, we need to run tests on test cluster with
enabled new JSON reader to see if there are any regressions.
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> Merge row set-based JSON reader
> -------------------------------
>
> Key: DRILL-6953
> URL: https://issues.apache.org/jira/browse/DRILL-6953
> Project: Apache Drill
> Issue Type: Improvement
> Affects Versions: 1.15.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Major
> Fix For: Future
>
>
> The final step in the ongoing "result set loader" saga is to merge the
> revised JSON reader into master. This reader does two key things:
> * Demonstrates the prototypical "late schema" style of data reading (discover
> schema while reading).
> * Implements many tricks and hacks to handle schema changes while loading.
> * Shows that, even with all these tricks, the only true solution is to
> actually have a schema.
> The new JSON reader:
> * Uses an expanded state machine when parsing rather than the complex set of
> if-statements in the current version.
> * Handles reading a run of nulls before seeing the first data value (as long
> as the data value shows up in the first record batch).
> * Uses the result-set loader to generate fixed-size batches regardless of the
> complexity, depth of structure, or width of variable-length fields.
> While the JSON reader itself is helpful, the key contribution is that it
> shows how to use the entire kit of parts: result set loader, projection
> framework, and so on. Since the projection framework can handle an external
> schema, it is also a handy foundation for the ongoing schema project.
> Key work to complete after this merger will be to reconcile actual data with
> the external schema. For example, if we know a column is supposed to be a
> VarChar, then read the column as a VarChar regardless of the type JSON itself
> picks. Or, if a column is supposed to be a Double, then convert Int and
> String JSON values into Doubles.
> The Row Set framework was designed to allow inserting custom column writers.
> This would be a great opportunity to do the work needed to create them. Then,
> use the new JSON framework to allow parsing a JSON field as a specified Drill
> type.
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