[
https://issues.apache.org/jira/browse/DRILL-6953?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17020809#comment-17020809
]
ASF GitHub Bot commented on DRILL-6953:
---------------------------------------
paul-rogers commented on issue #1913: DRILL-6953: EVF-based version of the JSON
reader
URL: https://github.com/apache/drill/pull/1913#issuecomment-577025711
@vvysotskyi, thanks for the note. If we're OK with the multi-step plan, I'll
go ahead and run a full test myself (with the reader turned off) to make sure
we're still good after rebasing and the small fixes includes since. I'll post
here once that is done.
Good suggestion on the JIRA tickets. Since each PR needs a ticket, we'd need
to fine them for that purpose anyway. You've probably seen the discussion on
the dev list about some nasty ambiguities related to the way DICT interacts
with some of our problem-child types. I filed a big, long ticket for that one.
I'll file additional tickets for the other issues as I reproduce them.
----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
[email protected]
> 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.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
