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Fix conditional joins with empty left table (#9146)
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Resolves #9044 by ensuring that when the left table is empty the functions short-circuit accordingly. Where necessary (i.e. for full joins) the complementary pairs of indices are returned.

Authors:
  - Vyas Ramasubramani (https://github.com/vyasr)

Approvers:
  - Nghia Truong (https://github.com/ttnghia)

URL: #9146
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@vyasr
vyasr authored Sep 8, 2021
1 parent b10835c commit 665c07e
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Showing 2 changed files with 60 additions and 10 deletions.
52 changes: 42 additions & 10 deletions cpp/src/join/conditional_join.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -50,9 +50,8 @@ conditional_join(table_view const& left,
// null index for the right table; in others, we return an empty output.
if (right.num_rows() == 0) {
switch (join_type) {
// Left, left anti, and full (which are effectively left because we are
// guaranteed that left has more rows than right) all return a all the
// row indices from left with a corresponding NULL from the right.
// Left, left anti, and full all return all the row indices from left
// with a corresponding NULL from the right.
case join_kind::LEFT_JOIN:
case join_kind::LEFT_ANTI_JOIN:
case join_kind::FULL_JOIN: return get_trivial_left_join_indices(left, stream);
Expand All @@ -61,6 +60,23 @@ conditional_join(table_view const& left,
case join_kind::LEFT_SEMI_JOIN:
return std::make_pair(std::make_unique<rmm::device_uvector<size_type>>(0, stream, mr),
std::make_unique<rmm::device_uvector<size_type>>(0, stream, mr));
default: CUDF_FAIL("Invalid join kind."); break;
}
} else if (left.num_rows() == 0) {
switch (join_type) {
// Left, left anti, left semi, and inner joins all return empty sets.
case join_kind::LEFT_JOIN:
case join_kind::LEFT_ANTI_JOIN:
case join_kind::INNER_JOIN:
case join_kind::LEFT_SEMI_JOIN:
return std::make_pair(std::make_unique<rmm::device_uvector<size_type>>(0, stream, mr),
std::make_unique<rmm::device_uvector<size_type>>(0, stream, mr));
// Full joins need to return the trivial complement.
case join_kind::FULL_JOIN: {
auto ret_flipped = get_trivial_left_join_indices(right, stream);
return std::make_pair(std::move(ret_flipped.second), std::move(ret_flipped.first));
}
default: CUDF_FAIL("Invalid join kind."); break;
}
}

Expand Down Expand Up @@ -113,7 +129,12 @@ conditional_join(table_view const& left,
join_size = size.value(stream);
}

// If the output size will be zero, we can return immediately.
// The initial early exit clauses guarantee that we will not reach this point
// unless both the left and right tables are non-empty. Under that
// constraint, neither left nor full joins can return an empty result since
// at minimum we are guaranteed null matches for all non-matching rows. In
// all other cases (inner, left semi, and left anti joins) if we reach this
// point we can safely return an empty result.
if (join_size == 0) {
return std::make_pair(std::make_unique<rmm::device_uvector<size_type>>(0, stream, mr),
std::make_unique<rmm::device_uvector<size_type>>(0, stream, mr));
Expand Down Expand Up @@ -174,20 +195,31 @@ std::size_t compute_conditional_join_output_size(table_view const& left,
rmm::cuda_stream_view stream,
rmm::mr::device_memory_resource* mr)
{
// We can immediately filter out cases where the right table is empty. In
// some cases, we return all the rows of the left table with a corresponding
// null index for the right table; in others, we return an empty output.
// We can immediately filter out cases where one table is empty. In
// some cases, we return all the rows of the other table with a corresponding
// null index for the empty table; in others, we return an empty output.
if (right.num_rows() == 0) {
switch (join_type) {
// Left, left anti, and full (which are effectively left because we are
// guaranteed that left has more rows than right) all return a all the
// row indices from left with a corresponding NULL from the right.
// Left, left anti, and full all return all the row indices from left
// with a corresponding NULL from the right.
case join_kind::LEFT_JOIN:
case join_kind::LEFT_ANTI_JOIN:
case join_kind::FULL_JOIN: return left.num_rows();
// Inner and left semi joins return empty output because no matches can exist.
case join_kind::INNER_JOIN:
case join_kind::LEFT_SEMI_JOIN: return 0;
default: CUDF_FAIL("Invalid join kind."); break;
}
} else if (left.num_rows() == 0) {
switch (join_type) {
// Left, left anti, left semi, and inner joins all return empty sets.
case join_kind::LEFT_JOIN:
case join_kind::LEFT_ANTI_JOIN:
case join_kind::INNER_JOIN:
case join_kind::LEFT_SEMI_JOIN: return 0;
// Full joins need to return the trivial complement.
case join_kind::FULL_JOIN: return right.num_rows();
default: CUDF_FAIL("Invalid join kind."); break;
}
}

Expand Down
18 changes: 18 additions & 0 deletions cpp/tests/join/conditional_join_tests.cu
View file
Original file line number Diff line number Diff line change
Expand Up @@ -304,6 +304,11 @@ TYPED_TEST(ConditionalInnerJoinTest, TestOneColumnOneRowAllEqual)
this->test({{0}}, {{0}}, left_zero_eq_right_zero, {{0, 0}});
};

TYPED_TEST(ConditionalInnerJoinTest, TestOneColumnLeftEmpty)
{
this->test({{}}, {{3, 4, 5}}, left_zero_eq_right_zero, {});
};

TYPED_TEST(ConditionalInnerJoinTest, TestOneColumnTwoRowAllEqual)
{
this->test({{0, 1}}, {{0, 0}}, left_zero_eq_right_zero, {{0, 0}, {0, 1}});
Expand Down Expand Up @@ -489,6 +494,11 @@ TYPED_TEST(ConditionalLeftJoinTest, TestTwoColumnThreeRowSomeEqual)
{{0, 0}, {1, 1}, {2, JoinNoneValue}});
};

TYPED_TEST(ConditionalLeftJoinTest, TestOneColumnLeftEmpty)
{
this->test({{}}, {{3, 4, 5}}, left_zero_eq_right_zero, {});
};

TYPED_TEST(ConditionalLeftJoinTest, TestCompareRandomToHash)
{
// Generate columns of 10 repeats of the integer range [0, 10), then merge
Expand Down Expand Up @@ -560,6 +570,14 @@ TYPED_TEST(ConditionalFullJoinTest, TestOneColumnNoneEqual)
{JoinNoneValue, 2}});
};

TYPED_TEST(ConditionalFullJoinTest, TestOneColumnLeftEmpty)
{
this->test({{}},
{{3, 4, 5}},
left_zero_eq_right_zero,
{{JoinNoneValue, 0}, {JoinNoneValue, 1}, {JoinNoneValue, 2}});
};

TYPED_TEST(ConditionalFullJoinTest, TestTwoColumnThreeRowSomeEqual)
{
this->test({{0, 1, 2}, {10, 20, 30}},
Expand Down

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