Do not attempt to push down calls with offsets

We don't correctly handle pushdowns with offsets, so we just skip them
instead of returning erroneous results.

Author: JamesGuthrie

CHANGELOG.md

@@ -17,6 +17,9 @@ We use the following categories for changes:
 ### Added
 - Add Prometheus metrics support for Tracing [#1102]
 
+### Fixed
+- Disable push downs which use `offset`, as they are broken [#1129]
+
 ## [0.9.0] - 2022-02-02
 
 ### Added

pkg/pgmodel/querier/query_builder.go

@@ -242,6 +242,13 @@ func canAttemptPushdown(metadata *promqlMetadata) bool {
 	path := metadata.path // PromQL AST.
 	queryHints := metadata.queryHints
 	selectHints := metadata.selectHints
+	vs, isVectorSelector := queryHints.CurrentNode.(*parser.VectorSelector)
+	if isVectorSelector {
+		if vs.Offset != 0 || vs.OriginalOffset != 0 {
+			// We can't handle offsets in pushdowns
+			return false
+		}
+	}
 	return extension.ExtensionIsInstalled && queryHints != nil && !hasSubquery(path) && selectHints != nil
 }
 

pkg/tests/end_to_end_tests/promql_query_endpoint_test.go

@@ -2506,6 +2506,10 @@ func TestPromQLQueryEndpoint(t *testing.T) {
 			name:  "two pushdowns, same metric different matchers",
 			query: `sum(rate(metric_2{foo = "bar"}[5m]))/sum(rate(metric_2[5m]))`,
 		},
+		{
+			name:  "pushdown with offset and rate smaller than vector selector lookback",
+			query: `delta(metric_2[1m] offset 3m)`,
+		},
 	}
 	start := time.Unix(startTime/1000, 0)
 	end := time.Unix(endTime/1000, 0)