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https://issues.apache.org/jira/browse/DRILL-7572?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17038813#comment-17038813
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ASF GitHub Bot commented on DRILL-7572:
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paul-rogers commented on issue #1971: DRILL-7572: JSON structure parser
URL: https://github.com/apache/drill/pull/1971#issuecomment-587300916
@vvysotskyi, thanks for pointing out the question; I missed it when reading
the code comments.
Looked at `CountingJsonReader`. Looks like creates a series or rows, one per
input row, with just a bit field set to 1. This reader could do exactly the
same by projecting none of the columns and instead writing that bit = 1 value
for the start of each top-level object. The non-projected columns will
"free-wheel" over the incoming JSON.
A better solution is to actually return the count. Maybe we need another
option on the format plugin, `supportsCountPushDown()` so that we return the
per-file row count rather grind through the effort of making trivial rows.
EVF has support for this idea with its notion of "project none" which occurs
when the scan asks for now rows as in a `COUNT(*)`.
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> JSON structure parser
> ---------------------
>
> Key: DRILL-7572
> URL: https://issues.apache.org/jira/browse/DRILL-7572
> Project: Apache Drill
> Issue Type: Improvement
> Affects Versions: 1.18.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Major
> Fix For: 1.18.0
>
>
> DRILL-6953, PR #1913 provides an EVF-version of the JSON reader. The original
> plan was to commit a first draft, with the feature disabled, then evolve from
> there. Review comments suggested we ensure that the first PR pass all unit
> tests with the feature enabled. Another comment suggested the JSON parser
> portion be reusable for other format or storage plugins. All good ideas.
> The amount of change in the original PR was becoming too large. So, we'll go
> ahead and split the work into smaller portions.
> This ticket is for the "JSON structure parser." This parser accepts the token
> stream from the Jackson parser and provides a framework to create a tree
> structure that describes the data. To keep the code simple, to simplify
> tests, and to make review easier, the structure parser does not directly
> integrate with the rest of Drill. Instead, it provides a number of listener
> interfaces which the next level implements. (The next level will be in
> another PR.)
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