uses current local timestamp when recording purged values

CrdsGossipPull.purged_values is meant to record recently purged values
so that they are excluded from imminent pull requests, until the entire
cluster have synced to the updated value:
https://github.com/solana-labs/solana/blob/c826cddbb/core/src/crds_gossip_pull.rs#L449-L454

However, VersionedCrdsValue.local_timestamp represents the local time
when the value was last updated, and given that crds values may have
different timeouts based on stake, it does not necessarily represent how
recently the value was purged:
https://github.com/solana-labs/solana/blob/c826cddbb/core/src/crds.rs#L75-L76

As such, recording current local timestamp when purging values is more
appropriate. Additionally, purge_purged assumes that the purge_values is
sorted in timestamps when draining the old ones; which is not true if
those timestamps are VersionedCrdsValue.local_timestamp:
https://github.com/solana-labs/solana/blob/c826cddbb/core/src/crds_gossip_pull.rs#L563-L571

core/src/cluster_info.rs

@@ -1890,14 +1890,12 @@ impl ClusterInfo {
                 error!("crds table trim failed: {:?}", err);
             }
             Ok(purged_values) => {
+                let now = timestamp();
                 self.stats
                     .trim_crds_table_purged_values_count
                     .add_relaxed(purged_values.len() as u64);
-                gossip.pull.purged_values.extend(
-                    purged_values
-                        .into_iter()
-                        .map(|v| (v.value_hash, v.local_timestamp)),
-                );
+                let purged_values = purged_values.into_iter().map(|v| (v.value_hash, now));
+                gossip.pull.purged_values.extend(purged_values);
             }
         }
     }

core/src/crds.rs

@@ -73,7 +73,7 @@ pub struct VersionedCrdsValue {
     /// local time when inserted
     pub insert_timestamp: u64,
     /// local time when updated
-    pub local_timestamp: u64,
+    pub(crate) local_timestamp: u64,
     /// value hash
     pub value_hash: Hash,
 }

core/src/crds_gossip.rs

@@ -66,8 +66,7 @@ impl CrdsGossip {
                     .push
                     .process_push_message(&mut self.crds, from, val, now);
                 if let Ok(Some(val)) = res {
-                    self.pull
-                        .record_old_hash(val.value_hash, val.local_timestamp);
+                    self.pull.record_old_hash(val.value_hash, now);
                     Some(val)
                 } else {
                     None

core/src/crds_gossip_pull.rs

@@ -300,8 +300,7 @@ impl CrdsGossipPull {
         for caller in callers {
             let key = caller.label().pubkey();
             if let Ok(Some(val)) = crds.insert(caller, now) {
-                self.purged_values
-                    .push_back((val.value_hash, val.local_timestamp));
+                self.purged_values.push_back((val.value_hash, now));
             }
             crds.update_record_timestamp(&key, now);
         }
@@ -399,8 +398,7 @@ impl CrdsGossipPull {
                     owners.insert(label.pubkey());
                     success.push((label, hash, wc));
                     if let Some(val) = old {
-                        self.purged_values
-                            .push_back((val.value_hash, val.local_timestamp))
+                        self.purged_values.push_back((val.value_hash, now))
                     }
                 }
             }
@@ -555,7 +553,7 @@ impl CrdsGossipPull {
                 .into_iter()
                 .filter_map(|label| {
                     let val = crds.remove(&label)?;
-                    Some((val.value_hash, val.local_timestamp))
+                    Some((val.value_hash, now))
                 }),
         );
         self.purged_values.len() - num_purged_values
@@ -1335,7 +1333,7 @@ mod test {
         }
 
         // purge the value
-        node.purge_purged(1);
+        node.purge_purged(3);
         assert_eq!(node.purged_values.len(), 0);
     }
     #[test]