feat: Add subfields pushdown for cardinality function

presto-common/src/main/java/com/facebook/presto/common/Subfield.java

@@ -81,6 +81,31 @@ public String toString()
         }
     }
 
+    public static final class StructureOnly
+            implements PathElement
+    {
+        private static final StructureOnly STRUCTURE_ONLY = new StructureOnly();
+
+        private StructureOnly() {}
+
+        public static StructureOnly getInstance()
+        {
+            return STRUCTURE_ONLY;
+        }
+
+        @Override
+        public boolean isSubscript()
+        {
+            return true;
+        }
+
+        @Override
+        public String toString()
+        {
+            return "[$]";
+        }
+    }
+
     public static final class NestedField
             implements PathElement
     {
@@ -238,6 +263,11 @@ public static PathElement noSubfield()
         return NoSubfield.getInstance();
     }
 
+    public static PathElement structureOnly()
+    {
+        return StructureOnly.getInstance();
+    }
+
     @JsonCreator
     public Subfield(String path)
     {

presto-common/src/main/java/com/facebook/presto/common/SubfieldTokenizer.java

@@ -106,7 +106,7 @@ private Subfield.PathElement computeNext()
         }
 
         if (tryMatch(OPEN_BRACKET)) {
-            Subfield.PathElement token = tryMatch(QUOTE) ? matchQuotedSubscript() : tryMatch(WILDCARD) ? matchWildcardSubscript() : matchUnquotedSubscript();
+            Subfield.PathElement token = tryMatch(QUOTE) ? matchQuotedSubscript() : tryMatch(WILDCARD) ? matchWildcardSubscript() : tryMatch(DOLLAR) ? matchStructureOnlySubscript() : matchUnquotedSubscript();
 
             match(CLOSE_BRACKET);
             firstSegment = false;
@@ -151,6 +151,11 @@ private Subfield.PathElement matchDollarPathElement()
         return Subfield.noSubfield();
     }
 
+    private Subfield.PathElement matchStructureOnlySubscript()
+    {
+        return Subfield.structureOnly();
+    }
+
     private static boolean isUnquotedPathCharacter(char c)
     {
         return c == ':' || c == '$' || c == '-' || c == '/' || c == '@' || c == '|' || c == '#' || c == ' ' || c == '<' || c == '>' || isUnquotedSubscriptCharacter(c);

presto-docs/src/main/sphinx/admin/properties-session.rst

@@ -446,6 +446,17 @@ Use this to optimize the ``map_filter()`` and ``map_subset()`` function.
 
 It controls if subfields access is executed at the data source or not.
 
+``pushdown_subfields_for_cardinality``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+* **Type:** ``boolean``
+* **Default value:** ``false``
+
+Enable subfield pruning for the ``cardinality()`` function to skip reading keys and values.
+
+When enabled, the query optimizer can push down subfield pruning for cardinality operations,
+allowing the data source to skip reading the actual keys and values when only the cardinality
+(count of elements) is needed.
+
 ``schedule_splits_based_on_task_load``
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 * **Type:** ``boolean``

presto-hive/src/test/java/com/facebook/presto/hive/TestHiveLogicalPlanner.java

@@ -84,6 +84,7 @@
 import static com.facebook.presto.SystemSessionProperties.OPTIMIZE_METADATA_QUERIES_IGNORE_STATS;
 import static com.facebook.presto.SystemSessionProperties.PUSHDOWN_DEREFERENCE_ENABLED;
 import static com.facebook.presto.SystemSessionProperties.PUSHDOWN_SUBFIELDS_ENABLED;
+import static com.facebook.presto.SystemSessionProperties.PUSHDOWN_SUBFIELDS_FOR_CARDINALITY;
 import static com.facebook.presto.SystemSessionProperties.PUSHDOWN_SUBFIELDS_FOR_MAP_FUNCTIONS;
 import static com.facebook.presto.SystemSessionProperties.UTILIZE_UNIQUE_PROPERTY_IN_QUERY_PLANNING;
 import static com.facebook.presto.common.function.OperatorType.EQUAL;
@@ -1637,6 +1638,56 @@ public void testPushdownSubfieldsForMapFilter()
         assertUpdate("DROP TABLE test_pushdown_map_subfields");
     }
 
+    @Test
+    public void testPushdownSubfieldsForCardinality()
+    {
+        Session cardinalityPushdown = Session.builder(getSession())
+                .setSystemProperty(PUSHDOWN_SUBFIELDS_FOR_CARDINALITY, "true")
+                .build();
+
+        // Test simple cardinality pushdown for MAP
+        assertUpdate("CREATE TABLE test_pushdown_cardinality_map(id integer, x map(integer, double))");
+        assertPushdownSubfields(cardinalityPushdown, "SELECT t.id, cardinality(x) FROM test_pushdown_cardinality_map t", "test_pushdown_cardinality_map",
+                ImmutableMap.of("x", toSubfields("x[$]")));
+        assertUpdate("DROP TABLE test_pushdown_cardinality_map");
+
+        // Test cardinality pushdown for ARRAY
+        assertUpdate("CREATE TABLE test_pushdown_cardinality_array(id integer, arr array(bigint))");
+        assertPushdownSubfields(cardinalityPushdown, "SELECT t.id, cardinality(arr) FROM test_pushdown_cardinality_array t", "test_pushdown_cardinality_array",
+                ImmutableMap.of("arr", toSubfields("arr[$]")));
+        assertUpdate("DROP TABLE test_pushdown_cardinality_array");
+
+        // Test cardinality in WHERE clause
+        assertUpdate("CREATE TABLE test_pushdown_cardinality_where(id integer, features map(varchar, double))");
+        assertPushdownSubfields(cardinalityPushdown, "SELECT t.id FROM test_pushdown_cardinality_where t WHERE cardinality(features) > 10", "test_pushdown_cardinality_where",
+                ImmutableMap.of("features", toSubfields("features[$]")));
+        assertUpdate("DROP TABLE test_pushdown_cardinality_where");
+
+        // Test cardinality in aggregation
+        assertUpdate("CREATE TABLE test_pushdown_cardinality_agg(id integer, data map(integer, varchar))");
+        assertPushdownSubfields(cardinalityPushdown, "SELECT AVG(cardinality(data)) FROM test_pushdown_cardinality_agg", "test_pushdown_cardinality_agg",
+                ImmutableMap.of("data", toSubfields("data[$]")));
+        assertUpdate("DROP TABLE test_pushdown_cardinality_agg");
+
+        // Test multiple cardinalities
+        assertUpdate("CREATE TABLE test_pushdown_cardinality_multi(id integer, map1 map(integer, double), map2 map(varchar, integer))");
+        assertPushdownSubfields(cardinalityPushdown, "SELECT cardinality(map1), cardinality(map2) FROM test_pushdown_cardinality_multi", "test_pushdown_cardinality_multi",
+                ImmutableMap.of("map1", toSubfields("map1[$]"), "map2", toSubfields("map2[$]")));
+        assertUpdate("DROP TABLE test_pushdown_cardinality_multi");
+
+        // Test cardinality with complex expression
+        assertUpdate("CREATE TABLE test_pushdown_cardinality_expr(id integer, tags map(varchar, varchar))");
+        assertPushdownSubfields(cardinalityPushdown, "SELECT cardinality(tags) * 2 FROM test_pushdown_cardinality_expr", "test_pushdown_cardinality_expr",
+                ImmutableMap.of("tags", toSubfields("tags[$]")));
+        assertUpdate("DROP TABLE test_pushdown_cardinality_expr");
+
+        // Test cardinality on ARRAY of maps
+        assertUpdate("CREATE TABLE test_pushdown_cardinality_nested(id integer, arr_of_maps array(map(integer, varchar)))");
+        assertPushdownSubfields(cardinalityPushdown, "SELECT transform(arr_of_maps, m -> cardinality(m)) FROM test_pushdown_cardinality_nested", "test_pushdown_cardinality_nested",
+                ImmutableMap.of("arr_of_maps", toSubfields("arr_of_maps[*][$]")));
+        assertUpdate("DROP TABLE test_pushdown_cardinality_nested");
+    }
+
     @Test
     public void testPushdownSubfieldsAssorted()
     {

presto-main-base/src/main/java/com/facebook/presto/SystemSessionProperties.java

@@ -356,6 +356,7 @@ public final class SystemSessionProperties
     public static final String ADD_DISTINCT_BELOW_SEMI_JOIN_BUILD = "add_distinct_below_semi_join_build";
     public static final String UTILIZE_UNIQUE_PROPERTY_IN_QUERY_PLANNING = "utilize_unique_property_in_query_planning";
     public static final String PUSHDOWN_SUBFIELDS_FOR_MAP_FUNCTIONS = "pushdown_subfields_for_map_functions";
+    public static final String PUSHDOWN_SUBFIELDS_FOR_CARDINALITY = "pushdown_subfields_for_cardinality";
     public static final String MAX_SERIALIZABLE_OBJECT_SIZE = "max_serializable_object_size";
     public static final String EXPRESSION_OPTIMIZER_IN_ROW_EXPRESSION_REWRITE = "expression_optimizer_in_row_expression_rewrite";
     public static final String TABLE_SCAN_SHUFFLE_PARALLELISM_THRESHOLD = "table_scan_shuffle_parallelism_threshold";
@@ -2053,6 +2054,10 @@ public SystemSessionProperties(
                         "Enable subfield pruning for map functions, currently include map_subset and map_filter",
                         featuresConfig.isPushdownSubfieldForMapFunctions(),
                         false),
+                booleanProperty(PUSHDOWN_SUBFIELDS_FOR_CARDINALITY,
+                        "Enable subfield pruning for cardinality() function to skip reading keys and values",
+                        featuresConfig.isPushdownSubfieldForCardinality(),
+                        false),
                 longProperty(MAX_SERIALIZABLE_OBJECT_SIZE,
                         "Configure the maximum byte size of a serializable object in expression interpreters",
                         featuresConfig.getMaxSerializableObjectSize(),
@@ -3520,6 +3525,11 @@ public static boolean isPushSubfieldsForMapFunctionsEnabled(Session session)
         return session.getSystemProperty(PUSHDOWN_SUBFIELDS_FOR_MAP_FUNCTIONS, Boolean.class);
     }
 
+    public static boolean isPushSubfieldsForCardinalityEnabled(Session session)
+    {
+        return session.getSystemProperty(PUSHDOWN_SUBFIELDS_FOR_CARDINALITY, Boolean.class);
+    }
+
     public static boolean isUtilizeUniquePropertyInQueryPlanningEnabled(Session session)
     {
         return session.getSystemProperty(UTILIZE_UNIQUE_PROPERTY_IN_QUERY_PLANNING, Boolean.class);

presto-main-base/src/main/java/com/facebook/presto/sql/analyzer/FeaturesConfig.java

@@ -324,6 +324,7 @@ public class FeaturesConfig
     private boolean addExchangeBelowPartialAggregationOverGroupId;
     private boolean addDistinctBelowSemiJoinBuild;
     private boolean pushdownSubfieldForMapFunctions = true;
+    private boolean pushdownSubfieldForCardinality;
     private long maxSerializableObjectSize = 1000;
     private boolean utilizeUniquePropertyInQueryPlanning = true;
     private String expressionOptimizerUsedInRowExpressionRewrite = "";
@@ -3269,6 +3270,19 @@ public boolean isPushdownSubfieldForMapFunctions()
         return pushdownSubfieldForMapFunctions;
     }
 
+    @Config("optimizer.pushdown-subfield-for-cardinality")
+    @ConfigDescription("Enable subfield pruning for cardinality() function to skip reading keys and values")
+    public FeaturesConfig setPushdownSubfieldForCardinality(boolean pushdownSubfieldForCardinality)
+    {
+        this.pushdownSubfieldForCardinality = pushdownSubfieldForCardinality;
+        return this;
+    }
+
+    public boolean isPushdownSubfieldForCardinality()
+    {
+        return pushdownSubfieldForCardinality;
+    }
+
     @Config("optimizer.utilize-unique-property-in-query-planning")
     @ConfigDescription("Utilize the unique property of input columns in query planning")
     public FeaturesConfig setUtilizeUniquePropertyInQueryPlanning(boolean utilizeUniquePropertyInQueryPlanning)

presto-main-base/src/main/java/com/facebook/presto/sql/planner/optimizations/PushdownSubfields.java

@@ -93,11 +93,13 @@
 import java.util.stream.IntStream;
 
 import static com.facebook.presto.SystemSessionProperties.isLegacyUnnest;
+import static com.facebook.presto.SystemSessionProperties.isPushSubfieldsForCardinalityEnabled;
 import static com.facebook.presto.SystemSessionProperties.isPushSubfieldsForMapFunctionsEnabled;
 import static com.facebook.presto.SystemSessionProperties.isPushdownSubfieldsEnabled;
 import static com.facebook.presto.SystemSessionProperties.isPushdownSubfieldsFromArrayLambdasEnabled;
 import static com.facebook.presto.common.Subfield.allSubscripts;
 import static com.facebook.presto.common.Subfield.noSubfield;
+import static com.facebook.presto.common.Subfield.structureOnly;
 import static com.facebook.presto.common.type.TypeUtils.readNativeValue;
 import static com.facebook.presto.common.type.Varchars.isVarcharType;
 import static com.facebook.presto.metadata.BuiltInTypeAndFunctionNamespaceManager.JAVA_BUILTIN_NAMESPACE;
@@ -820,6 +822,7 @@ private static final class SubfieldExtractor
             private final FunctionAndTypeManager functionAndTypeManager;
             private final boolean isPushDownSubfieldsFromLambdasEnabled;
             private final boolean isPushdownSubfieldsForMapFunctionsEnabled;
+            private final boolean isPushdownSubfieldsForCardinalityEnabled;
 
             private SubfieldExtractor(
                     FunctionResolution functionResolution,
@@ -835,11 +838,26 @@ private SubfieldExtractor(
                 requireNonNull(session);
                 this.isPushDownSubfieldsFromLambdasEnabled = isPushdownSubfieldsFromArrayLambdasEnabled(session);
                 this.isPushdownSubfieldsForMapFunctionsEnabled = isPushSubfieldsForMapFunctionsEnabled(session);
+                this.isPushdownSubfieldsForCardinalityEnabled = isPushSubfieldsForCardinalityEnabled(session);
             }
 
             @Override
             public Void visitCall(CallExpression call, Context context)
             {
+                if (isPushdownSubfieldsForCardinalityEnabled && functionResolution.isCardinalityFunction(call.getFunctionHandle()) && call.getArguments().size() == 1) {
+                    RowExpression argument = call.getArguments().get(0);
+                    if (argument instanceof VariableReferenceExpression) {
+                        Type argumentType = argument.getType();
+                        if (argumentType instanceof MapType || argumentType instanceof ArrayType) {
+                            VariableReferenceExpression variable = (VariableReferenceExpression) argument;
+                            Subfield cardinalitySubfield = new Subfield(
+                                    variable.getName(),
+                                    ImmutableList.of(structureOnly()));
+                            context.subfields.add(cardinalitySubfield);
+                            return null;
+                        }
+                    }
+                }
                 ComplexTypeFunctionDescriptor functionDescriptor = functionAndTypeManager.getFunctionMetadata(call.getFunctionHandle()).getDescriptor();
                 if (isSubscriptOrElementAtFunction(call, functionResolution, functionAndTypeManager) || isMapSubSetWithConstantArray(call, functionResolution) || isMapFilterWithConstantFilterInMapKey(call, functionResolution)) {
                     Optional<List<Subfield>> subfield = toSubfield(call, functionResolution, expressionOptimizer, connectorSession, functionAndTypeManager, isPushdownSubfieldsForMapFunctionsEnabled);

presto-main-base/src/main/java/com/facebook/presto/sql/relational/FunctionResolution.java

@@ -439,6 +439,11 @@ public boolean isMapFilterFunction(FunctionHandle functionHandle)
         return functionAndTypeResolver.getFunctionMetadata(functionHandle).getName().equals(functionAndTypeResolver.qualifyObjectName(QualifiedName.of("map_filter")));
     }
 
+    public boolean isCardinalityFunction(FunctionHandle functionHandle)
+    {
+        return functionAndTypeResolver.getFunctionMetadata(functionHandle).getName().equals(functionAndTypeResolver.qualifyObjectName(QualifiedName.of("cardinality")));
+    }
+
     @Override
     public FunctionHandle lookupBuiltInFunction(String functionName, List<Type> inputTypes)
     {

presto-main-base/src/test/java/com/facebook/presto/sql/analyzer/TestFeaturesConfig.java

@@ -272,6 +272,7 @@ public void testDefaults()
                 .setAddExchangeBelowPartialAggregationOverGroupId(false)
                 .setAddDistinctBelowSemiJoinBuild(false)
                 .setPushdownSubfieldForMapFunctions(true)
+                .setPushdownSubfieldForCardinality(false)
                 .setUtilizeUniquePropertyInQueryPlanning(true)
                 .setExpressionOptimizerUsedInRowExpressionRewrite("")
                 .setInnerJoinPushdownEnabled(false)
@@ -505,6 +506,7 @@ public void testExplicitPropertyMappings()
                 .put("exclude-invalid-worker-session-properties", "true")
                 .put("optimizer.add-distinct-below-semi-join-build", "true")
                 .put("optimizer.pushdown-subfield-for-map-functions", "false")
+                .put("optimizer.pushdown-subfield-for-cardinality", "true")
                 .put("optimizer.utilize-unique-property-in-query-planning", "false")
                 .put("optimizer.expression-optimizer-used-in-expression-rewrite", "custom")
                 .put("optimizer.add-exchange-below-partial-aggregation-over-group-id", "true")
@@ -729,6 +731,7 @@ public void testExplicitPropertyMappings()
                 .setAddExchangeBelowPartialAggregationOverGroupId(true)
                 .setAddDistinctBelowSemiJoinBuild(true)
                 .setPushdownSubfieldForMapFunctions(false)
+                .setPushdownSubfieldForCardinality(true)
                 .setUtilizeUniquePropertyInQueryPlanning(false)
                 .setExpressionOptimizerUsedInRowExpressionRewrite("custom")
                 .setInEqualityJoinPushdownEnabled(true)