Isaac Zhu created IGNITE-13443:
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Summary: distributed left joins errored with
"java.lang.ClassCastException"
Key: IGNITE-13443
URL: https://issues.apache.org/jira/browse/IGNITE-13443
Project: Ignite
Issue Type: Bug
Components: h2-limitation
Affects Versions: 2.8.1
Reporter: Isaac Zhu
Attachments: JoinBatch.java
This is actually an H2 1.4.197 Bug
When using *distributed joins*, SQL like this (table A and table B are not
collocated, so distributed join is used here):
select * from table A left join table B on A.id = B.id left join table C
on B.id = C.id where ...
has chance to error out at the second left join with a
"java.lang.ClassCastException" when the first left join had an EmptyCursor
This is because, for distributed join, H2 JoinBatch is used - it seems
JoinBatch is not used for collocated join.
In JoinBatch line 292:
[https://github.com/h2database/h2database/blob/c8a861bb1a3f04967ec40cb5e3336535c43af5fb/h2/src/main/org/h2/table/JoinBatch.java#L292]
It increases the filter ID to let the next fetchCurrent call resolve the
"EMPTY_CURSOR" to a NullRow when a "JoinFilter.find" is not called.
Then, in the "find" call, the resolved NullRow will be updated to some cursor
from the future - because only EmptyCursor is skipped in the find(), a NullRow
will be updated again and the bitwise state goes wrong
This then causes the exception in "fetchCurrent" line: 358
[https://github.com/h2database/h2database/blob/c8a861bb1a3f04967ec40cb5e3336535c43af5fb/h2/src/main/org/h2/table/JoinBatch.java#L358]
The "x" is a Future, so it can't be cast to a Cursor - the state is wrong, the
"isFuture" returns false while it is a Future.
I did a local fix in our server as a workaround in org.h2.table.JoinBatch, the
changed code is attached.
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