fix: DH-20516: Default property sense (and documentation) was inverted.

docs/groovy/conceptual/query-engine/parallelization.md

@@ -86,7 +86,7 @@ To explicitly mark a `Selectable` or `Filter` as stateful, use the `withSerial`
 
 - A serial `Filter` cannot be reordered with respect to other `Filter`s. Every input row to a stateful `Filter` is evaluated in order.
 - When a `Selectable` is serial, then every row for that column is evaluated in order.
-- For `Selectable`s, additional ordering constraints are controlled by the value of the `QueryTable.SERIAL_SELECT_IMPLICIT_BARRIERS`. This is set by the property `QueryTable.serialSelectImplicitBarriers` (defaulting to the value of `QueryTable.statelessSelectByDefault`).
+- For `Selectable`s, additional ordering constraints are controlled by the value of the `QueryTable.SERIAL_SELECT_IMPLICIT_BARRIERS`. This is set by the property `QueryTable.serialSelectImplicitBarriers`. The default value is the inverse of `QueryTable.statelessSelectByDefault`. When `Selectables` are stateless by default, no implicit barriers are added (i.e., `QueryTable.SERIAL_SELECT_IMPLICIT_BARRIERS` is false). When `Selectables` are stateful by default, then implicit barriers are added (i.e. `QueryTable.SERIAL_SELECT_IMPLICIT_BARRIERS` is true).
 - If `QueryTable.SERIAL_SELECT_IMPLICIT_BARRIERS` is false, no additional ordering between expressions is imposed. As with every `select` or `update` call, if column B references column A, then the necessary inputs to column B from column A are evaluated before column B is evaluated. To impose further ordering constraints, use barriers.
 - If `QueryTable.SERIAL_SELECT_IMPLICIT_BARRIERS` is true, then a serial `Selectable` is an absolute barrier with respect to all other serial `Selectable`s. This prohibits serial `Selectable`s from being evaluated concurrently, permitting them to access global state. `Selectable`s that are not serial may be reordered with respect to a serial selectable.
 

engine/table/src/main/java/io/deephaven/engine/table/impl/QueryTable.java

@@ -320,10 +320,16 @@ public interface MemoizableOperation<T extends DynamicNode & NotificationStepRec
     /**
      * If set to true, then stateful SelectColumns form implicit barriers. If set to false, then StatefulSelectColumns
      * do not form implicit barriers.
+     *
+     * <p>
+     * When stateless selectables are on by default ({@code QueryTable.statelessSelectByDefault=true}), no implicit
+     * barriers are added (i.e., this defaults to false). When stateless columns are off by default
+     * ({@code QueryTable.statelessSelectByDefault=false}), implicit barriers are added (i.e., this defaults to true).
+     * </p>
      */
     public static boolean SERIAL_SELECT_IMPLICIT_BARRIERS =
             Configuration.getInstance().getBooleanWithDefault("QueryTable.serialSelectImplicitBarriers",
-                    STATELESS_SELECT_BY_DEFAULT);
+                    !STATELESS_SELECT_BY_DEFAULT);
 
     private static final AtomicReferenceFieldUpdater<QueryTable, ModifiedColumnSet> MODIFIED_COLUMN_SET_UPDATER =
             AtomicReferenceFieldUpdater.newUpdater(QueryTable.class, ModifiedColumnSet.class, "modifiedColumnSet");

engine/table/src/test/java/io/deephaven/engine/table/impl/QueryTableSelectBarrierTest.java

@@ -42,6 +42,13 @@ public class QueryTableSelectBarrierTest {
     // then you can increase this amount to run the tests many times.
     private static final int REPEATS_FOR_CONFIDENCE = 1;
 
+    @Test
+    public void testPropertyDefaults() {
+        assertFalse(QueryTable.STATELESS_FILTERS_BY_DEFAULT);
+        assertFalse(QueryTable.STATELESS_SELECT_BY_DEFAULT);
+        assertTrue(QueryTable.SERIAL_SELECT_IMPLICIT_BARRIERS);
+    }
+
     @Test
     public void testRepeatedBarrierSelectColumn() {
         for (int ii = 0; ii < REPEATS_FOR_CONFIDENCE; ++ii) {