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https://issues.apache.org/jira/browse/DRILL-8507?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17877894#comment-17877894
]
ASF GitHub Bot commented on DRILL-8507:
---------------------------------------
paul-rogers commented on code in PR #2937:
URL: https://github.com/apache/drill/pull/2937#discussion_r1737180959
##########
exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/columnreaders/ParquetSchema.java:
##########
@@ -227,12 +251,14 @@ public void createNonExistentColumns(OutputMutator
output, List<NullableIntVecto
* @throws SchemaChangeException should not occur
*/
- private NullableIntVector createMissingColumn(SchemaPath col, OutputMutator
output) throws SchemaChangeException {
- // col.toExpr() is used here as field name since we don't want to see
these fields in the existing maps
- MaterializedField field = MaterializedField.create(col.toExpr(),
-
Types.optional(TypeProtos.MinorType.INT));
- return (NullableIntVector) output.addField(field,
- TypeHelper.getValueVectorClass(TypeProtos.MinorType.INT,
DataMode.OPTIONAL));
+ private ValueVector createMissingColumn(SchemaPath col, OutputMutator
output) throws SchemaChangeException {
+ String colName = col.getAsUnescapedPath();
+ MaterializedField tableField = tableSchema.column(colName);
+ TypeProtos.MinorType type = tableField == null ? TypeProtos.MinorType.INT
: tableField.getType().getMinorType();
+ MaterializedField field = MaterializedField.create(colName,
Review Comment:
This is a good change: we are propagating the old column type. This is
consistent with EVF.
However, this stuff is horribly complex. If we reuse the column, we **must**
reuse the actual value vector. Otherwise, you'll get crashes in the downstream
operators that are bound to that vector. The binding is redone only on a schema
change. But, your fix avoids the schema change, and hence prevents the
rebinding.
Also, note that this fix works ONLY in one direction (column appears, then
disappears), and ONLY within a single thread: it can't solve the same problem
if the two files are read in different threads and sent to the SORT to
reconcile.
Further, we are changing the mode to `OPTIONAL` as required so we can fill
the vector with `NULL` values. However, change of mode (i.e. nullability)
**is** a schema change and will cause the SORT to fail. We have to have known,
on the previous file, that the column will be missing in this file, so that we
can create the original column as `OPTIONAL`.
> Missing parquet columns quoted with backticks conflict with existing ones
> -------------------------------------------------------------------------
>
> Key: DRILL-8507
> URL: https://issues.apache.org/jira/browse/DRILL-8507
> Project: Apache Drill
> Issue Type: Bug
> Affects Versions: 1.21.2
> Reporter: Yaroslav
> Priority: Major
> Attachments: people.tar.gz
>
>
> {*}NOTE{*}: I worked on this issue along with DRILL-8508. It turned out that
> it required this bug to get fixed first. And since these 2 are about a little
> bit different things it was decided to report them as separate issues. So,
> I'm going to link this issue as a requirement for that issue and open one PR
> for both (if it's allowed..). I think single PR would make it easier to
> review the code since the issues are quite related anyway.
> h3. Prerequisites
> If a {{ParquetRecordReader}} doesn't find a selected column, it creates a
> null-filled {{NullableIntVector}} with the column's name and the correct
> value count set. The field name for the vector is derived from
> {{SchemaPath#toExpr}} method, which always enquotes the outcome string with
> backticks.
> h3. Problems
> This causes some wrong field name equality checks (comparing two strings of
> field names, non-quoted and quoted, returns false, but essentially is
> supposed to return true) that lead to some errors.
> For example, the errors occur when you select a column from a table where
> some parquet files contain it and some do not. Consider a {{dfs.tmp.people}}
> table with such parquet files and their schemas:
> {code:java}
> /tmp/people/0.parquet: id<INT(REQUIRED)> | name<VARCHAR(OPTIONAL)> |
> age<INT(OPTIONAL)>
> /tmp/people/1.parquet: id<INT(REQUIRED)>{code}
> Now let's try to use an operator that doesn't support schema change. For
> example, {{{}ORDER BY{}}}:
> {code:java}
> apache drill> SELECT age FROM dfs.tmp.people ORDER BY age;
> Error: UNSUPPORTED_OPERATION ERROR: Schema changes not supported in External
> Sort. Please enable Union type.
> Previous schema: BatchSchema [fields=[[`age` (INT:OPTIONAL)]],
> selectionVector=NONE]
> Incoming schema: BatchSchema [fields=[[`age` (INT:OPTIONAL)], [``age``
> (INT:OPTIONAL)]], selectionVector=NONE]
> Fragment: 0:0
> [Error Id: d3efffd4-cf31-46d5-9f6a-141a61e71d12 on node2.vmcluster.com:31010]
> (state=,code=0)
> {code}
> ORDER BY error clearly shows us that ``age`` is an extra column here and the
> incoming schema should only have the unquoted field to match the previous
> schema.
> Another example is in {{UNION ALL}} operator:
> {code:java}
> apache drill> SELECT age FROM dfs.tmp.people UNION ALL (VALUES (1));
> Error: SYSTEM ERROR: IllegalArgumentException: Input batch and output batch
> have different field counthas!
> Fragment: 0:0
> Please, refer to logs for more information.
> [Error Id: 81680275-92ee-4d1b-93b5-14f4068990eb on node2.vmcluster.com:31010]
> (state=,code=0)
> {code}
> Again, "different field counts" issue is caused by an extra quoted column
> that counts as different field.
> h3. Solution
> The solution for these errors would be to replace {{SchemaPath#toExpr}} call
> with {{{}SchemaPath#getAsUnescapedPath{}}}, which doesn't enquote the outcome
> string. Simply enough, but note that we used to use
> {{SchemaPath#getAsUnescapedPath}} before DRILL-4264 where we switched to
> {{{}SchemaPath#toExpr{}}}. The author even put a comment:
> {code:java}
> // col.toExpr() is used here as field name since we don't want to see these
> fields in the existing maps{code}
> So it looks like moving to {{SchemaPath#toExpr}} was a conscious decision.
> But, honestly, I don't really understand the motivation for this, even with
> the comment. I don't really understand what "existing maps" are here. Maybe
> someone from the community can help here, but I will further consider it as a
> mistake, simply because it causes the above problems.
> h3. Regressions
> The change brings some regressions detected by unit tests. Those I found fail
> because they changed their execution flow after the fix in these places:
> *
> [FieldIdUtil#getFieldId|https://github.com/apache/drill/blob/7c813ff6440a118de15f552145b40eb07bb8e7a2/exec/java-exec/src/main/java/org/apache/drill/exec/vector/complex/FieldIdUtil.java#L206]
> *
> [ScanBatch$Mutator#addField|https://github.com/apache/drill/blob/097a4717ac998ec6bf3c70a99575c7ff53f47430/exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/ScanBatch.java#L523-L524]
> Before the fix, the field name equality checks returned false from comparing
> quoted and unquoted field names. The failing tests relied on that behavior
> and worked only with this condition. But after the fix, when we compare two
> quoted names and return true, we fall to a different branch and the tests
> aren't ready for that.
> But obviously the change _is fixing the problem_ so the tests that relied on
> that problem should now be adjusted.
> Please see more technical details on each failed unit test in the linked PR.
>
>
>
>
>
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