Skip to content

Fix #233 Add limit pushdown to attached queries #313

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 7 commits into
base: main
Choose a base branch
from
Open
Show file tree
Hide file tree
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
1 change: 1 addition & 0 deletions src/include/postgres_scanner.hpp
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ struct PostgresBindData : public FunctionData {
string schema_name;
string table_name;
string sql;
string limit;
idx_t pages_approx = 0;

vector<PostgresType> postgres_types;
Expand Down
8 changes: 4 additions & 4 deletions src/postgres_scanner.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -252,14 +252,14 @@ static void PostgresInitInternal(ClientContext &context, const PostgresBindData
if (bind_data->table_name.empty()) {
D_ASSERT(!bind_data->sql.empty());
lstate.sql = StringUtil::Format(
R"(COPY (SELECT %s FROM (%s) AS __unnamed_subquery %s) TO STDOUT (FORMAT "binary");)",
col_names, bind_data->sql, filter);
R"(COPY (SELECT %s FROM (%s) AS __unnamed_subquery %s%s) TO STDOUT (FORMAT "binary");)",
col_names, bind_data->sql, filter, bind_data->limit);

} else {
lstate.sql = StringUtil::Format(
R"(COPY (SELECT %s FROM %s.%s %s) TO STDOUT (FORMAT "binary");)",
R"(COPY (SELECT %s FROM %s.%s %s%s) TO STDOUT (FORMAT "binary");)",
col_names, KeywordHelper::WriteQuoted(bind_data->schema_name, '"'),
KeywordHelper::WriteQuoted(bind_data->table_name, '"'), filter);
KeywordHelper::WriteQuoted(bind_data->table_name, '"'), filter, bind_data->limit);
}
lstate.exec = false;
lstate.done = false;
Expand Down
66 changes: 66 additions & 0 deletions src/storage/postgres_optimizer.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -3,15 +3,79 @@
#include "storage/postgres_transaction.hpp"
#include "storage/postgres_optimizer.hpp"
#include "duckdb/planner/operator/logical_get.hpp"
#include "duckdb/planner/operator/logical_limit.hpp"
#include "storage/postgres_catalog.hpp"
#include "postgres_scanner.hpp"


namespace duckdb {

struct PostgresOperators {
reference_map_t<PostgresCatalog, vector<reference<LogicalGet>>> scans;
};

static void OptimizePostgresScanLimitPushdown(unique_ptr<LogicalOperator> &op) {
if (op->type == LogicalOperatorType::LOGICAL_LIMIT) {
auto &limit = op->Cast<LogicalLimit>();
reference<LogicalOperator> child = *op->children[0];

while (child.get().type == LogicalOperatorType::LOGICAL_PROJECTION) {
child = *child.get().children[0];
}

if (child.get().type != LogicalOperatorType::LOGICAL_GET) {
OptimizePostgresScanLimitPushdown(op->children[0]);
return;
}

auto &get = child.get().Cast<LogicalGet>();
if (!PostgresCatalog::IsPostgresScan(get.function.name)) {
OptimizePostgresScanLimitPushdown(op->children[0]);
return;
}

switch (limit.limit_val.Type()) {
case LimitNodeType::CONSTANT_VALUE:
case LimitNodeType::UNSET:
break;
default:
// not a constant or unset limit
OptimizePostgresScanLimitPushdown(op->children[0]);
return;
}
switch (limit.offset_val.Type()) {
case LimitNodeType::CONSTANT_VALUE:
case LimitNodeType::UNSET:
break;
default:
// not a constant or unset offset
OptimizePostgresScanLimitPushdown(op->children[0]);
return;
}

auto &bind_data = get.bind_data->Cast<PostgresBindData>();

string generated_limit_clause = "";
if (limit.limit_val.Type() != LimitNodeType::UNSET) {
generated_limit_clause += " LIMIT " + to_string(limit.limit_val.GetConstantValue());
}
if (limit.offset_val.Type() != LimitNodeType::UNSET) {
generated_limit_clause += " OFFSET " + to_string(limit.offset_val.GetConstantValue());
}

if (!generated_limit_clause.empty()) {
bind_data.limit = generated_limit_clause;

op = std::move(op->children[0]);
return;
}
}

for (auto &child : op->children) {
OptimizePostgresScanLimitPushdown(child);
}
}

void GatherPostgresScans(LogicalOperator &op, PostgresOperators &result) {
if (op.type == LogicalOperatorType::LOGICAL_GET) {
auto &get = op.Cast<LogicalGet>();
Expand All @@ -35,6 +99,8 @@ void GatherPostgresScans(LogicalOperator &op, PostgresOperators &result) {
}

void PostgresOptimizer::Optimize(OptimizerExtensionInput &input, unique_ptr<LogicalOperator> &plan) {
// look at query plan and check if we can find LIMIT/OFFSET to pushdown
OptimizePostgresScanLimitPushdown(plan);
// look at the query plan and check if we can enable streaming query scans
PostgresOperators operators;
GatherPostgresScans(*plan, operators);
Expand Down
31 changes: 31 additions & 0 deletions test/sql/storage/limit.test
Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
# name: test/sql/storage/limit.test
# description: Test limit on an attached table
# group: [storage]

require postgres_scanner

require-env POSTGRES_TEST_DATABASE_AVAILABLE

statement ok
ATTACH 'dbname=postgresscanner' AS s (TYPE POSTGRES)

statement ok
CREATE OR REPLACE TABLE s.large_tbl AS FROM range(100000) t(i)

query I
FROM s.large_tbl LIMIT 5
----
0
1
2
3
4

query I
FROM s.large_tbl LIMIT 5 OFFSET 5
----
5
6
7
8
9
Loading