shauryachats opened a new pull request, #14198:
URL: https://github.com/apache/pinot/pull/14198
The current logical planner has a shortcoming for `NOT IN` subqueries where
it projects unused columns before the exchange stage, resulting in increased
data during shuffles and significantly increasing latency.
An example would be:
```
EXPLAIN PLAN FOR SELECT count(*) FROM a WHERE a.col1 = 'foo' and a.col2 =
'bar' AND a.col4 = 12 AND a.col5 = false AND a.col3 NOT IN (SELECT b.col3 FROM
b where b.col3 = 'baz') AND a.col3 NOT IN (SELECT b.col3 FROM b where b.col3 =
'qux'))
```
The execution plan is:
```
Execution Plan
PinotLogicalAggregate(group=[{}], agg#0=[COUNT($0)])
PinotLogicalExchange(distribution=[hash])
PinotLogicalAggregate(group=[{}], agg#0=[COUNT()])
LogicalFilter(condition=[IS NOT TRUE($8)])
LogicalJoin(condition=[=($6, $7)], joinType=[left])
PinotLogicalExchange(distribution=[hash[6]])
LogicalProject(col1=[$0], col2=[$1], col4=[$3], col5=[$4],
col30=[$5], $f1=[$7], col32=[$2])
LogicalFilter(condition=[IS NOT TRUE($7)])
LogicalJoin(condition=[=($5, $6)], joinType=[left])
PinotLogicalExchange(distribution=[hash[5]])
LogicalProject(col1=[$0], col2=[$1], col3=[$2],
col4=[$3], col5=[$4], col30=[$2])
LogicalFilter(condition=[AND(=($0, _UTF-8'foo'), =($1,
_UTF-8'bar'), =($3, 12), NOT($4))])
LogicalTableScan(table=[[default, a]])
PinotLogicalExchange(distribution=[hash[0]])
PinotLogicalAggregate(group=[{0}], agg#0=[MIN($1)])
PinotLogicalExchange(distribution=[hash[0]])
PinotLogicalAggregate(group=[{0}], agg#0=[MIN($1)])
LogicalProject(col3=[$2], $f1=[true])
LogicalFilter(condition=[=($2,
CAST(_UTF-8'baz'):INTEGER NOT NULL)])
LogicalTableScan(table=[[default, b]])
PinotLogicalExchange(distribution=[hash[0]])
PinotLogicalAggregate(group=[{0}], agg#0=[MIN($1)])
PinotLogicalExchange(distribution=[hash[0]])
PinotLogicalAggregate(group=[{0}], agg#0=[MIN($1)])
LogicalProject(col3=[$2], $f1=[true])
LogicalFilter(condition=[=($2, CAST(_UTF-8'qux'):INTEGER
NOT NULL)])
LogicalTableScan(table=[[default, b]])
```
It can be observed from the execution plan
```
PinotLogicalExchange(distribution=[hash[5]])
LogicalProject(col1=[$0], col2=[$1], col3=[$2],
col4=[$3], col5=[$4], col30=[$2])
```
that while the join is only on `a.col3` and the final result required is a
`count(*)`, other columns (`col1`, `col2`, `col4`, `col5`) are present in the
`LogicalProject` step right before `PinotLogicalExchange` which should ideally
have been pruned.
The cause of the issue is the `LogicalFilter` which does not allow projects
to be transposed, since the current rules do not have
`PROJECT_FILTER_TRANSPOSE` included. Even if `PROJECT_FILTER_TRANSPOSE` is
included in `BASIC_RULES`, it would not work for multiple joins since
`BASIC_RULES` optimizations are run only once.
This PR aims to fix this issue by running `Project` pushdown (transpose and
merge operations) as a `RuleCollection` after the first iteration of `Filter`
pushdown rules are run to ensure `Project` can be pushed down as much as
possible.
After the `Project` pushdown is run, the `Filter` pushdown is run again to
push down filters after the project pushdown for two reasons:
- In a generic query, filter pushdowns are generally more selective than
project pushdowns and should be given more priority.
- Major changes to the current logical plans should be avoided, and not
running a `Filter` pushdown after `Project` pushdown results in a Project
pushdown after each logical plan node which increases verbosity.
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