kasakrisz commented on pull request #1324:
URL: https://github.com/apache/hive/pull/1324#issuecomment-666155487
@HunterL
Thanks for reviewing this patch.
The expression
```
filterExpr: (((s_floor_space > 1000) and s_store_sk is not null) or
s_store_sk is not null)
```
is a result of merging two `TableScanOperator`s. Both of them are scanning
the same table: `alias: s` but they had different `filterExpr`.
TS1: ((s_floor_space > 1000) and s_store_sk is not null)
TS2: s_store_sk is not null
SharedWorkOptimizer naively combined the filter expressions using `or`
because we need the union of the records produced by both TS. You are right in
this particular case the filter expression could be reduced to `s_store_sk is
not null`
The new TS has two children
```
TableScan
alias: s
filterExpr: (((s_floor_space > 1000) and s_store_sk is not null) or
s_store_sk is not null) (type: boolean)
Filter Operator
predicate: ((s_floor_space > 1000) and s_store_sk is not null) (type:
boolean)
...
Filter Operator
predicate: s_store_sk is not null (type: boolean)
...
```
both of them are `Filter operators` which are the root of subtrees to
broadcast the proper subset of records to each reducer edge (Reducer 2 and
Reducer 3)
If `and` were used for combining the filter expressions of TS operators the
branch which does not have the filter `s_floor_space > 1000` would loose a
subset of records.
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