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https://issues.apache.org/jira/browse/DRILL-7306?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16875606#comment-16875606
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ASF GitHub Bot commented on DRILL-7306:
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paul-rogers commented on issue #1813: DRILL-7306: Disable schema-only batch for
new scan framework
URL: https://github.com/apache/drill/pull/1813#issuecomment-506989680
Addressed the TestEmptyInputSql failure. The code now recognizes two cases:
1. Empty results: the reader provided a schema, but had no rows. (This is
the case that failed.)
2. Null results: the reader provides neither rows nor schema. This is the
case that was always being followed, even if we have a schema.
Changed the query builder row set code to return an empty row set if the
output contains only an empty batch and contains a schema. The code continues
to return no row set if the result is null. (Oddly, Drill will return a batch
with no rows and no schema if the reader returns no batches at all.)
Will address other issues in separate commits.
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> Disable "fast schema" batch for new scan framework
> --------------------------------------------------
>
> Key: DRILL-7306
> URL: https://issues.apache.org/jira/browse/DRILL-7306
> Project: Apache Drill
> Issue Type: Bug
> Affects Versions: 1.16.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Major
> Labels: ready-to-commit
> Fix For: 1.17.0
>
>
> The EVF framework is set up to return a "fast schema" empty batch with only
> schema as its first batch because, when the code was written, it seemed
> that's how we wanted operators to work. However, DRILL-7305 notes that many
> operators cannot handle empty batches.
> Since the empty-batch bugs show that Drill does not, in fact, provide a "fast
> schema" batch, this ticket asks to disable the feature in the new scan
> framework. The feature is disabled with a config option; it can be re-enabled
> if ever it is needed.
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