Add a histogram metric tracking evaluated query plans

.changesets/feat_geal_evaluate_plan_count.md

@@ -0,0 +1,6 @@
+### Add a histogram metric tracking evaluated query plans ([PR #5875](https://github.com/apollographql/router/pull/5875))
+
+The `supergraph.query_planning.experimental_plans_limit` option can be used to limit the number of query plans evaluated for a query, to reduce the time spent planning. When reaching that limit, the planner would still return a valid query plan, but maybe the most optimized one.
+This adds the `apollo.router.query_planning.plan.evaluated_plans` histogram metric to track the number of evaluated query plans, giving more context to configure this option.
+
+By [@Geal](https://github.com/Geal) in https://github.com/apollographql/router/pull/5875

Cargo.lock

@@ -5630,9 +5630,9 @@ dependencies = [
 
 [[package]]
 name = "router-bridge"
-version = "0.6.0+v2.9.0"
+version = "0.6.1+v2.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "96ef4910ade6753863c8437a76e88e236ab91688dcfe739d73417ae7848f3b92"
+checksum = "b3be2d3ebbcbceb19dc813f5cee507295c673bb4e3f7a7cd532c8c27c95f92fc"
 dependencies = [
  "anyhow",
  "async-channel 1.9.0",

apollo-router/Cargo.toml

@@ -197,7 +197,7 @@ regex = "1.10.5"
 reqwest.workspace = true
 
 # note: this dependency should _always_ be pinned, prefix the version with an `=`
-router-bridge = "=0.6.0+v2.9.0"
+router-bridge = "=0.6.1+v2.9.0"
 
 rust-embed = { version = "8.4.0", features = ["include-exclude"] }
 rustls = "0.21.12"

apollo-router/src/query_planner/bridge_query_planner.rs

@@ -304,13 +304,19 @@ impl PlannerMode {
                 if let Some(node) = &mut root_node {
                     init_query_plan_root_node(node)?;
                 }
+
                 Ok(PlanSuccess {
                     usage_reporting,
                     data: QueryPlanResult {
                         formatted_query_plan: Some(Arc::new(plan.to_string())),
                         query_plan: QueryPlan {
                             node: root_node.map(Arc::new),
                         },
+                        evaluated_plan_count: plan
+                            .statistics
+                            .evaluated_plan_count
+                            .clone()
+                            .into_inner() as u64,
                     },
                 })
             }
@@ -532,6 +538,7 @@ impl BridgeQueryPlanner {
                     QueryPlanResult {
                         query_plan: QueryPlan { node: Some(node) },
                         formatted_query_plan,
+                        evaluated_plan_count,
                     },
                 mut usage_reporting,
             } => {
@@ -549,6 +556,12 @@ impl BridgeQueryPlanner {
                     doc.clone()
                 };
 
+                u64_histogram!(
+                    "apollo.router.query_planning.plan.evaluated_plans",
+                    "Number of query plans evaluated for a query before choosing the best one",
+                    evaluated_plan_count
+                );
+
                 let generated_usage_reporting = generate_usage_reporting(
                     &signature_doc.executable,
                     &doc.executable,
@@ -844,6 +857,7 @@ impl BridgeQueryPlanner {
 pub struct QueryPlanResult {
     pub(super) formatted_query_plan: Option<Arc<String>>,
     pub(super) query_plan: QueryPlan,
+    pub(super) evaluated_plan_count: u64,
 }
 
 impl QueryPlanResult {
@@ -1595,4 +1609,23 @@ mod tests {
             "init.is_success" = false
         );
     }
+
+    #[test(tokio::test)]
+    async fn test_evaluated_plans_histogram() {
+        async {
+            let _ = plan(
+                EXAMPLE_SCHEMA,
+                include_str!("testdata/query.graphql"),
+                include_str!("testdata/query.graphql"),
+                None,
+                PlanOptions::default(),
+            )
+            .await
+            .unwrap();
+
+            assert_histogram_exists!("apollo.router.query_planning.plan.evaluated_plans", u64);
+        }
+        .with_metrics()
+        .await;
+    }
 }

docs/source/configuration/telemetry/instrumentation/standard-instruments.mdx

@@ -66,6 +66,7 @@ The coprocessor operations metric has the following attributes:
 - `apollo.router.query_planning.plan.duration` - Histogram of plan durations isolated to query planning time only.
 - `apollo.router.query_planning.total.duration` - Histogram of plan durations including queue time.
 - `apollo.router.query_planning.queued` - A gauge of the number of queued plans requests.
+- `apollo.router.query_planning.plan.evaluated_plans` - Histogram of the number of evaluated query plans.
 - `apollo.router.v8.heap.used` - heap memory used by V8, in bytes.
 - `apollo.router.v8.heap.total` - total heap allocated by V8, in bytes.
 

fuzz/Cargo.toml

@@ -20,7 +20,7 @@ reqwest = { workspace = true, features = ["json", "blocking"] }
 serde_json.workspace = true
 tokio.workspace = true
 # note: this dependency should _always_ be pinned, prefix the version with an `=`
-router-bridge = "=0.6.0+v2.9.0"
+router-bridge = "=0.6.1+v2.9.0"
 
 [dev-dependencies]
 anyhow = "1"