limits gossip vote stats to the top most voted slots (#22416)

gossip/src/cluster_info_metrics.rs

@@ -4,6 +4,7 @@ use {
     solana_measure::measure::Measure,
     solana_sdk::{clock::Slot, pubkey::Pubkey},
     std::{
+        cmp::Reverse,
         collections::HashMap,
         ops::{Deref, DerefMut},
         sync::atomic::{AtomicU64, Ordering},
@@ -564,20 +565,8 @@ pub(crate) fn submit_gossip_stats(
         ("all-push", crds_stats.push.fails.iter().sum::<usize>(), i64),
         ("all-pull", crds_stats.pull.fails.iter().sum::<usize>(), i64),
     );
-    for (slot, num_votes) in &crds_stats.pull.votes {
-        datapoint_info!(
-            "cluster_info_crds_stats_votes_pull",
-            ("slot", *slot, i64),
-            ("num_votes", *num_votes, i64),
-        );
-    }
-    for (slot, num_votes) in &crds_stats.push.votes {
-        datapoint_info!(
-            "cluster_info_crds_stats_votes_push",
-            ("slot", *slot, i64),
-            ("num_votes", *num_votes, i64),
-        );
-    }
+    submit_vote_stats("cluster_info_crds_stats_votes_pull", &crds_stats.pull.votes);
+    submit_vote_stats("cluster_info_crds_stats_votes_push", &crds_stats.push.votes);
     let votes: HashMap<Slot, usize> = crds_stats
         .pull
         .votes
@@ -592,11 +581,20 @@ pub(crate) fn submit_gossip_stats(
         )
         .into_grouping_map()
         .aggregate(|acc, _slot, num_votes| Some(acc.unwrap_or_default() + num_votes));
-    for (slot, num_votes) in votes {
-        datapoint_info!(
-            "cluster_info_crds_stats_votes",
-            ("slot", slot, i64),
-            ("num_votes", num_votes, i64),
-        );
+    submit_vote_stats("cluster_info_crds_stats_votes", &votes);
+}
+
+fn submit_vote_stats<'a, I>(name: &'static str, votes: I)
+where
+    I: IntoIterator<Item = (&'a Slot, /*num-votes:*/ &'a usize)>,
+{
+    // Submit vote stats only for the top most voted slots.
+    const NUM_SLOTS: usize = 20;
+    let mut votes: Vec<_> = votes.into_iter().map(|(k, v)| (*k, *v)).collect();
+    if votes.len() > NUM_SLOTS {
+        votes.select_nth_unstable_by_key(NUM_SLOTS, |(_, num)| Reverse(*num));
+    }
+    for (slot, num_votes) in votes.into_iter().take(NUM_SLOTS) {
+        datapoint_info!(name, ("slot", slot, i64), ("num_votes", num_votes, i64),);
     }
 }