[
https://issues.apache.org/jira/browse/DRILL-7479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16995009#comment-16995009
]
ASF GitHub Bot commented on DRILL-7479:
---------------------------------------
paul-rogers commented on issue #1923: DRILL-7479: Partial fixes for metadata
parameterized type issues
URL: https://github.com/apache/drill/pull/1923#issuecomment-565141768
Tried making `ColumnStatistics` generic. However there are several places
where the type of the column is required (min/max values, for example.)
The issue is that each column has multiple stats: some are of the same type
as the column (min, max, histogram), others are not (HLL, NDV.)
Even those that are the "same" type as the column are not: the column is of
type `VARCHAR`, but the `ColumnStatistics` is of type `String`, say. There is
no mapping from Drill to Java types; this knowedge appears to be implicit in
the code.
Further, the `ColumnStatisticsKind` is not what you would think: it has a
compile-time type (the type parameter), but, because of type erasure, no
runtime type (I cannot ask what kind of value the kind holds.)
I think we need to rethink this a bit:
* A type definition holds the type-specific logic (such as merging stats) as
well as giving both the Java and SQL type (if any) for the stat.
* A mapping tells us the Java stats type for the SQL type.
* A stats definition holds a name and a type definition. (Where the type
definition may be "same as column type.")
* A Statistic has a definition, a (possibly implied) type and a value.
* A column is generic: it has a name, a SQL type and a list of statistics.
* It may be worthwhile having a column "meta-meta" definition: the list of
statistics valid for a column of a given SQL type. (There is no min or max for
a VarBinary, say.)
This PR at least removes many warnings an obscure compile error from the
present design.
----------------------------------------------------------------
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]
> Short-term fixes for metadata API parameterized type issues
> -----------------------------------------------------------
>
> Key: DRILL-7479
> URL: https://issues.apache.org/jira/browse/DRILL-7479
> Project: Apache Drill
> Issue Type: Task
> Affects Versions: 1.17.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Blocker
> Fix For: 1.17.0
>
>
> See DRILL-7480 for a discussion of the issues with how we currently use
> parameterized types in the metadata API.
> This ticket is for short-term fixes that convert unsafe generic types of the
> form {{StatisticsHolder}} to the form {{StatisticsHolder<?>}} so that the
> compiler does not complain with many warnings (and a few Eclipse-only errors.)
> The topic should be revisited later in the context of DRILL-7480.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
