mustafasrepo commented on code in PR #11875:
URL: https://github.com/apache/datafusion/pull/11875#discussion_r1707228670
##########
datafusion/core/src/dataframe/mod.rs:
##########
@@ -3019,11 +3019,11 @@ mod tests {
assert_batches_sorted_eq!(
[
- "+-----+-----+----+-------+",
Review Comment:
Result of this test changes with this PR. I have analyzed the change,
previously this tes was generating the following plan:
```
"ProjectionExec: expr=[c1@0 as c1, c2@1 as c2, c3@2 as c3, CAST(c2@1 AS
Int8) + c3@2 as sum]",
" RepartitionExec: partitioning=RoundRobinBatch(8), input_partitions=1",
" SortExec: expr=[c1@0 ASC,c2@1 ASC,c3@2 ASC],
preserve_partitioning=[false]",
" GlobalLimitExec: skip=0, fetch=1",
" CoalescePartitionsExec",
" CoalesceBatchesExec: target_batch_size=8192, fetch=1",
" FilterExec: c2@1 = 3 AND c1@0 = a",
" RepartitionExec: partitioning=RoundRobinBatch(8),
input_partitions=1",
" CsvExec: file_groups={1 group: [[<PATH>]]},
projection=[c1, c2, c3], has_header=true",
```
After the changes in this PR, following plan is generated
```
"ProjectionExec: expr=[c1@0 as one, c2@1 as two, c3@2 as c3, CAST(c2@1
AS Int8) + c3@2 as total]",
" RepartitionExec: partitioning=RoundRobinBatch(8), input_partitions=1",
" SortExec: TopK(fetch=1), expr=[c3@2 ASC],
preserve_partitioning=[false]",
" CoalescePartitionsExec",
" CoalesceBatchesExec: target_batch_size=8192",
" FilterExec: c2@1 = 3 AND c1@0 = a",
" RepartitionExec: partitioning=RoundRobinBatch(8),
input_partitions=1",
" CsvExec: file_groups={1 group: [[<PATH>]]},
projection=[c1, c2, c3], has_header=true",
```
I think the second plan generates a deterministic result. However, the query
(dataframe query) is not deterministic as is.
With this observation, I have updated the place of the limit to make sure
the query is deterministic after execution. With the change of the place of the
limit, the following plan is generated:
```
"ProjectionExec: expr=[c1@0 as one, c2@1 as two, c3@2 as c3, CAST(c2@1
AS Int8) + c3@2 as total]",
" GlobalLimitExec: skip=0, fetch=1",
" SortPreservingMergeExec: [c1@0 ASC,c2@1 ASC,c3@2 ASC], fetch=1",
" SortExec: TopK(fetch=1), expr=[c3@2 ASC],
preserve_partitioning=[true]",
" CoalesceBatchesExec: target_batch_size=8192",
" FilterExec: c2@1 = 3 AND c1@0 = a",
" RepartitionExec: partitioning=RoundRobinBatch(8),
input_partitions=1",
" CsvExec: file_groups={1 group: [[<PATH>]]},
projection=[c1, c2, c3], has_header=true",
```
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