fix(query-engine): validate sliding counter bounds early

Author: milindsrivastava1997

asap-query-engine/src/engines/simple_engine/mod.rs

@@ -1883,6 +1883,26 @@ impl SimpleEngine {
         use crate::engines::query_result::RangeVectorElement;
         use crate::engines::window_merger::create_window_merger;
 
+        if context.window_type == WindowType::Sliding
+            && context.tumbling_window_ms > 0
+            && matches!(
+                context.base.metadata.statistic_to_compute,
+                Statistic::Increase | Statistic::Rate
+            )
+        {
+            if let Some(&off_grid_timestamp) = context
+                .output_timestamps
+                .iter()
+                .find(|&&timestamp| !timestamp.is_multiple_of(context.tumbling_window_ms))
+            {
+                return Err(format!(
+                    "Exact Prometheus counter bounds are unavailable for off-grid Sliding \
+                     timestamp {} (grid interval {}ms)",
+                    off_grid_timestamp, context.tumbling_window_ms
+                ));
+            }
+        }
+
         let lookback_ms = (context.lookback_bucket_count as u64) * context.tumbling_window_ms;
 
         // Step 1: Fetch all data needed for the entire range. Sliding
@@ -2137,20 +2157,6 @@ impl SimpleEngine {
         // (#581). One loop shape for topk and non-topk alike, rather than
         // maintaining two.
         for &current_time in &context.output_timestamps {
-            if context.window_type == WindowType::Sliding
-                && context.tumbling_window_ms > 0
-                && matches!(
-                    context.base.metadata.statistic_to_compute,
-                    Statistic::Increase | Statistic::Rate
-                )
-                && !current_time.is_multiple_of(context.tumbling_window_ms)
-            {
-                return Err(format!(
-                    "Exact Prometheus counter bounds are unavailable for off-grid Sliding \
-                     timestamp {} (grid interval {}ms)",
-                    current_time, context.tumbling_window_ms
-                ));
-            }
             let current_time_i64 = i64::try_from(current_time)
                 .map_err(|_| "Output timestamp exceeds signed timestamp range".to_string())?;
             let query_range_ms = i64::try_from(context.query_range_ms)

asap-query-engine/src/tests/native_range_query_tests.rs

@@ -154,35 +154,35 @@ mod tests {
         let host = Some(vec!["host-a".to_string()]);
         let data = vec![
             (
-                1_000,
+                10_000,
                 host.clone(),
                 Box::new(IncreaseAccumulator::new_with_sample_count(
                     crate::data_model::Measurement::new(100.0),
-                    0,
+                    9_000,
                     crate::data_model::Measurement::new(110.0),
-                    1_000,
+                    10_000,
                     2,
                 )) as Box<dyn AggregateCore>,
             ),
             (
-                2_000,
+                11_000,
                 host.clone(),
                 Box::new(IncreaseAccumulator::new_with_sample_count(
                     crate::data_model::Measurement::new(110.0),
-                    1_000,
+                    10_000,
                     crate::data_model::Measurement::new(120.0),
-                    2_000,
+                    11_000,
                     2,
                 )) as Box<dyn AggregateCore>,
             ),
             (
-                3_000,
+                12_000,
                 host,
                 Box::new(IncreaseAccumulator::new_with_sample_count(
                     crate::data_model::Measurement::new(120.0),
-                    2_000,
+                    11_000,
                     crate::data_model::Measurement::new(130.0),
-                    3_000,
+                    12_000,
                     2,
                 )) as Box<dyn AggregateCore>,
             ),
@@ -199,11 +199,28 @@ mod tests {
         );
 
         // The stored Sliding windows are aligned to the 1s grid, so native
-        // execution cannot represent the exact [t-2s, t] range at t=1.5s.
+        // execution cannot represent the exact [t-2s, t] range at t=10.5s.
         // Returning None lets the caller use an exact Prometheus fallback.
-        assert!(engine
-            .handle_range_query_promql("rate(http_requests_total[2s])".to_string(), 1.5, 2.5, 1.0,)
-            .is_none());
+        assert!(
+            engine
+                .handle_range_query_promql(
+                    "rate(http_requests_total[2s])".to_string(),
+                    10.5,
+                    12.5,
+                    1.0,
+                )
+                .is_none()
+        );
+
+        let (_, on_grid_result) = engine
+            .handle_range_query_promql("rate(http_requests_total[2s])".to_string(), 11.0, 12.0, 1.0)
+            .expect("on-grid Sliding counter query should use native execution");
+        let on_grid_samples = matrix_values(on_grid_result)
+            .into_iter()
+            .find(|element| element.labels.labels.contains(&"host-a".to_string()))
+            .expect("host-a result missing")
+            .samples;
+        assert_eq!(on_grid_samples.len(), 2);
     }
 
     /// Checks every `(label_values, ts, expected_present, reason)` case