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https://issues.apache.org/jira/browse/DRILL-6953?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17019745#comment-17019745
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ASF GitHub Bot commented on DRILL-6953:
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cgivre commented on issue #1913: DRILL-6953: EVF-based version of the JSON
reader
URL: https://github.com/apache/drill/pull/1913#issuecomment-576433165
I would vote for option one. IMHO we should work for smaller PRs so that we
can get code committed faster and hopefully less work for the reviewers.
Sent from my iPhone
> On Jan 20, 2020, at 16:16, Paul Rogers <[email protected]> wrote:
>
>
> @vvysotskyi, @arina-ielchiieva - it turns out that a number of fixes are
required to resolve the issues that came up in the tests run above. The full
set of changes, with JSON and all the fixes, will be large. We should break
them into smaller PRs.
>
> There are two ways to proceed. One is to commit this PR with the new
reader disabled by default. Then apply fixes one by one for easier to review.
Eventually, we enable the new reader when everything works.
>
> The other is that I make the fixes on this branch, then pull each out into
a separate PR that we review before this one. The result is much extra work for
me to do all the code copying/merging involved.
>
> How do you recommend we proceed?
>
> —
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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: Sub-task
> Affects Versions: 1.15.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Major
> Labels: doc-impacting
> Fix For: 1.18.0
>
>
> 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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