Fix the getBlobs metric and ensure it is recorded promptly to prevent miscounts (#7188)

From testing conducted by Sunnyside Labs, they noticed that the "expected blobs" are quite low on bandwidth constrained nodes. This observation revealed that we don't record the `beacon_blobs_from_el_expected_total` metric at all if the EL doesn't return any response. The fetch blobs function returns without recording the metric.

To fix this, I've moved `BLOBS_FROM_EL_EXPECTED_TOTAL` and `BLOBS_FROM_EL_RECEIVED_TOTAL` to as early as possible, to make the metric more accurate.

beacon_node/beacon_chain/src/fetch_blobs.rs

@@ -13,7 +13,7 @@ use crate::observed_data_sidecars::DoNotObserve;
 use crate::{metrics, AvailabilityProcessingStatus, BeaconChain, BeaconChainTypes, BlockError};
 use execution_layer::json_structures::BlobAndProofV1;
 use execution_layer::Error as ExecutionLayerError;
-use metrics::{inc_counter, inc_counter_by, TryExt};
+use metrics::{inc_counter, TryExt};
 use ssz_types::FixedVector;
 use state_processing::per_block_processing::deneb::kzg_commitment_to_versioned_hash;
 use std::sync::Arc;
@@ -73,13 +73,20 @@ pub async fn fetch_and_process_engine_blobs<T: BeaconChainTypes>(
         .as_ref()
         .ok_or(FetchEngineBlobError::ExecutionLayerMissing)?;
 
+    metrics::observe(&metrics::BLOBS_FROM_EL_EXPECTED, num_expected_blobs as f64);
     debug!(num_expected_blobs, "Fetching blobs from the EL");
     let response = execution_layer
         .get_blobs(versioned_hashes)
         .await
+        .inspect_err(|_| {
+            inc_counter(&metrics::BLOBS_FROM_EL_ERROR_TOTAL);
+        })
         .map_err(FetchEngineBlobError::RequestFailed)?;
 
-    if response.is_empty() || response.iter().all(|opt| opt.is_none()) {
+    let num_fetched_blobs = response.iter().filter(|opt| opt.is_some()).count();
+    metrics::observe(&metrics::BLOBS_FROM_EL_RECEIVED, num_fetched_blobs as f64);
+
+    if num_fetched_blobs == 0 {
         debug!(num_expected_blobs, "No blobs fetched from the EL");
         inc_counter(&metrics::BLOBS_FROM_EL_MISS_TOTAL);
         return Ok(None);
@@ -99,20 +106,6 @@ pub async fn fetch_and_process_engine_blobs<T: BeaconChainTypes>(
         &chain.spec,
     )?;
 
-    let num_fetched_blobs = fixed_blob_sidecar_list
-        .iter()
-        .filter(|b| b.is_some())
-        .count();
-
-    inc_counter_by(
-        &metrics::BLOBS_FROM_EL_EXPECTED_TOTAL,
-        num_expected_blobs as u64,
-    );
-    inc_counter_by(
-        &metrics::BLOBS_FROM_EL_RECEIVED_TOTAL,
-        num_fetched_blobs as u64,
-    );
-
     // Gossip verify blobs before publishing. This prevents blobs with invalid KZG proofs from
     // the EL making it into the data availability checker. We do not immediately add these
     // blobs to the observed blobs/columns cache because we want to allow blobs/columns to arrive on gossip

beacon_node/beacon_chain/src/metrics.rs

@@ -1662,28 +1662,37 @@ pub static DATA_COLUMN_SIDECAR_GOSSIP_VERIFICATION_TIMES: LazyLock<Result<Histog
 pub static BLOBS_FROM_EL_HIT_TOTAL: LazyLock<Result<IntCounter>> = LazyLock::new(|| {
     try_create_int_counter(
         "beacon_blobs_from_el_hit_total",
-        "Number of blob batches fetched from the execution layer",
+        "Number of non-empty blob batches fetched from the execution layer",
     )
 });
 
 pub static BLOBS_FROM_EL_MISS_TOTAL: LazyLock<Result<IntCounter>> = LazyLock::new(|| {
     try_create_int_counter(
         "beacon_blobs_from_el_miss_total",
-        "Number of blob batches failed to fetch from the execution layer",
+        "Number of empty blob responses from the execution layer",
     )
 });
 
-pub static BLOBS_FROM_EL_EXPECTED_TOTAL: LazyLock<Result<IntCounter>> = LazyLock::new(|| {
+pub static BLOBS_FROM_EL_ERROR_TOTAL: LazyLock<Result<IntCounter>> = LazyLock::new(|| {
     try_create_int_counter(
-        "beacon_blobs_from_el_expected_total",
+        "beacon_blobs_from_el_error_total",
+        "Number of failed blob fetches from the execution layer",
+    )
+});
+
+pub static BLOBS_FROM_EL_EXPECTED: LazyLock<Result<Histogram>> = LazyLock::new(|| {
+    try_create_histogram_with_buckets(
+        "beacon_blobs_from_el_expected",
         "Number of blobs expected from the execution layer",
+        Ok(vec![0.0, 3.0, 6.0, 9.0, 12.0, 18.0, 24.0, 30.0]),
     )
 });
 
-pub static BLOBS_FROM_EL_RECEIVED_TOTAL: LazyLock<Result<IntCounter>> = LazyLock::new(|| {
+pub static BLOBS_FROM_EL_RECEIVED: LazyLock<Result<Histogram>> = LazyLock::new(|| {
-    try_create_int_counter(
+    try_create_histogram_with_buckets(
         "beacon_blobs_from_el_received_total",
         "Number of blobs fetched from the execution layer",
+        linear_buckets(0.0, 4.0, 20),
     )
 });