mihaibudiu commented on code in PR #5384:
URL: https://github.com/apache/calcite/pull/5384#discussion_r4446229057
##########
core/src/main/java/org/apache/calcite/rex/RexUtil.java:
##########
@@ -1823,20 +1832,44 @@ private static boolean isFlat(
* calls to an associative operator such as AND and OR.
*/
public static boolean isFlat(RexNode expr) {
- if (!(expr instanceof RexCall)) {
- return true;
+ // Use an explicit stack to avoid StackOverflowError on deeply nested
+ // expressions (e.g. CALCITE-5845)
+ final Deque<RexNode> stack = new ArrayDeque<>();
+ stack.push(expr);
+ while (!stack.isEmpty()) {
+ final RexNode current = stack.pop();
+ if (!(current instanceof RexCall)) {
+ continue;
+ }
+ final RexCall call = (RexCall) current;
+ if (!isFlat(call.getOperands(), call.getOperator())) {
Review Comment:
I haven't checked if this function may be recursive.
##########
core/src/test/java/org/apache/calcite/rex/RexUtilTest.java:
##########
@@ -43,4 +54,116 @@ class RexUtilTest {
RexUtil.SubQueryFinder.find(expression, SqlKind.SCALAR_QUERY));
assertNull(RexUtil.SubQueryFinder.find(expression, SqlKind.EXISTS));
}
+
+ /** Test case for
+ * <a
href="https://issues.apache.org/jira/browse/CALCITE-5845";>[CALCITE-5845]
+ * StackOverflowError when SQL has a very large predicate with many ANDs</a>.
+ *
+ * <p>Verifies that {@link RexUtil#flattenAnd} does not recurse when given a
Review Comment:
Strictly speaking it's not checking the lack of recursion, but the ability
to compute with a small stack.
##########
core/src/test/java/org/apache/calcite/rex/RexUtilTest.java:
##########
@@ -43,4 +54,116 @@ class RexUtilTest {
RexUtil.SubQueryFinder.find(expression, SqlKind.SCALAR_QUERY));
assertNull(RexUtil.SubQueryFinder.find(expression, SqlKind.EXISTS));
}
+
+ /** Test case for
+ * <a
href="https://issues.apache.org/jira/browse/CALCITE-5845";>[CALCITE-5845]
+ * StackOverflowError when SQL has a very large predicate with many ANDs</a>.
+ *
+ * <p>Verifies that {@link RexUtil#flattenAnd} does not recurse when given a
+ * deeply nested binary AND tree. */
+ @Test void testFlattenAndDeeplyNested() {
+ final RelBuilder builder =
+ RelBuilder.create(Frameworks.newConfigBuilder().build());
+ final RexBuilder rexBuilder = builder.getCluster().getRexBuilder();
+ final RelDataType booleanType =
+ builder.getTypeFactory().createSqlType(SqlTypeName.BOOLEAN);
+ final int depth = 20_000;
+ // Build AND(AND(AND(..., $1), $2), $3, ...) as a left-deep binary tree,
+ // iteratively. Hash codes are pre-warmed bottom-up so that the
+ // de-duplication set inside flattenAnd does not itself recurse deeply.
+ RexNode node = rexBuilder.makeInputRef(booleanType, 0);
+ node.hashCode();
+ for (int i = 1; i < depth; i++) {
+ node =
+ rexBuilder.makeCall(SqlStdOperatorTable.AND, node,
+ rexBuilder.makeInputRef(booleanType, i));
+ node.hashCode();
+ }
+ final RexNode deepTree = node;
+ final List<RexNode> flat =
+ runInSmallStack(() -> RexUtil.flattenAnd(ImmutableList.of(deepTree)));
+ assertThat(flat, hasSize(depth));
+ }
+
+ /** Test case for
+ * <a
href="https://issues.apache.org/jira/browse/CALCITE-5845";>[CALCITE-5845]
+ * StackOverflowError when SQL has a very large predicate with many ANDs</a>.
+ *
+ * <p>Verifies that {@link RexUtil#flatten} does not recurse when given a
+ * deeply nested binary AND tree. */
+ @Test void testFlattenDeeplyNested() {
+ final RelBuilder builder =
+ RelBuilder.create(Frameworks.newConfigBuilder().build());
+ final RexBuilder rexBuilder = builder.getCluster().getRexBuilder();
+ final RelDataType booleanType =
+ builder.getTypeFactory().createSqlType(SqlTypeName.BOOLEAN);
+ final int depth = 20_000;
+ RexNode node = rexBuilder.makeInputRef(booleanType, 0);
+ for (int i = 1; i < depth; i++) {
+ node =
+ rexBuilder.makeCall(SqlStdOperatorTable.AND, node,
+ rexBuilder.makeInputRef(booleanType, i));
+ }
+ final RexNode deepTree = node;
+ final List<RexNode> flat =
+ runInSmallStack(
+ () -> RexUtil.flatten(ImmutableList.of(deepTree),
+ SqlStdOperatorTable.AND));
+ assertThat(flat, hasSize(depth));
+ }
+
+ /** Test case for
+ * <a
href="https://issues.apache.org/jira/browse/CALCITE-5845";>[CALCITE-5845]
+ * StackOverflowError when SQL has a very large predicate with many ANDs</a>.
+ *
+ * <p>Verifies that {@link RexUtil#isFlat(RexNode)} does not recurse when
+ * given a deeply nested tree of a non-associative operator (NOT), where
+ * short-circuiting at the top level is not possible. */
+ @Test void testIsFlatDeeplyNested() {
+ final RelBuilder builder =
+ RelBuilder.create(Frameworks.newConfigBuilder().build());
+ final RexBuilder rexBuilder = builder.getCluster().getRexBuilder();
+ final RelDataType booleanType =
+ builder.getTypeFactory().createSqlType(SqlTypeName.BOOLEAN);
+ final int depth = 20_000;
+ RexNode node = rexBuilder.makeInputRef(booleanType, 0);
+ for (int i = 0; i < depth; i++) {
+ node = rexBuilder.makeCall(SqlStdOperatorTable.NOT, node);
+ }
+ final RexNode deepTree = node;
+ assertThat(runInSmallStack(() -> RexUtil.isFlat(deepTree)), is(true));
+ }
+
+ /** Runs {@code callable} on a thread with a small stack, so that a recursive
+ * implementation of the callee overflows quickly, while an iterative
+ * implementation completes. */
+ private static <T> T runInSmallStack(Callable<T> callable) {
Review Comment:
how does this differ from the other function with the same name?
##########
core/src/main/java/org/apache/calcite/plan/RelOptUtil.java:
##########
@@ -2593,47 +2605,59 @@ public static void decomposeConjunction(
@Nullable RexNode rexPredicate,
List<RexNode> rexList,
List<RexNode> notList) {
- if (rexPredicate == null || rexPredicate.isAlwaysTrue()) {
+ // Use an explicit stack to avoid StackOverflowError on deeply nested ANDs
Review Comment:
only ANDs or deep expressions in general?
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