srowen commented on a change in pull request #26650: [CORE] Fix a bug in
getBlockHosts
URL: https://github.com/apache/spark/pull/26650#discussion_r349927646
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File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/PartitionedFileUtil.scala
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@@ -69,8 +69,8 @@ object PartitionedFileUtil {
b.getHosts -> (b.getOffset + b.getLength - offset).min(length)
// The fragment ends at a position within this block
- case b if offset <= b.getOffset && offset + length < b.getLength =>
- b.getHosts -> (offset + length - b.getOffset).min(length)
+ case b if offset <= b.getOffset && offset + length < b.getOffset +
b.getLength =>
Review comment:
This change looks correct.
I think there's another issue. This is checking where the end of the
argument block is, so it should look for where `offset + length` is relative to
b. Shouldn't the first condition be `offset + length >= b.getOffset`? Otherwise
this is handling the case where the argument doesn't overlap at all with b --
imagine offset is much smaller than b.getOffset.
The result here could be negative. I think that's masked by the fact that
these are filtered for size > 0 below, and so I guess the logic ends up
correct, in that these are not considered. It might be worth adjusting for
clarity as it took me a few minutes to reason about why this was different.
Anyway, in this case, the argument isn't fully contained in b (that is
handled in the case above actually, by `.min(length)` -- might update the
comment). Then it's true that the `.min()` below is not needed.
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