From ee54ce47278140204f889bb1415fdef662c1c19d Mon Sep 17 00:00:00 2001
From: Anatoly Yakovenko <aeyakovenko@gmail.com>
Date: Thu, 14 Jun 2018 22:03:49 -0700
Subject: [PATCH] min table size before purge

---
 src/crdt.rs | 44 +++++++++++++++++++++++++++++++-------------
 1 file changed, 31 insertions(+), 13 deletions(-)

diff --git a/src/crdt.rs b/src/crdt.rs
index c893b66a9e..ab9c287274 100644
--- a/src/crdt.rs
+++ b/src/crdt.rs
@@ -34,8 +34,12 @@ use std::time::Duration;
 use streamer::{BlobReceiver, BlobSender, Window};
 use timing::timestamp;
 
+/// milliseconds we sleep for between gossip requests
 const GOSSIP_SLEEP_MILLIS: u64 = 100;
 
+/// minimum membership table size before we start purging dead nodes
+const MIN_TABLE_SIZE: usize = 2;
+
 pub fn parse_port_or_addr(optstr: Option<String>) -> SocketAddr {
     let daddr: SocketAddr = "0.0.0.0:8000".parse().expect("default socket address");
     if let Some(addrstr) = optstr {
@@ -263,26 +267,29 @@ impl Crdt {
     /// http://asc.di.fct.unl.pt/~jleitao/pdf/dsn07-leitao.pdf
     /// challenging part is that we are on a permissionless network
     pub fn purge(&mut self, now: u64) {
+        if self.table.len() <= MIN_TABLE_SIZE {
+            return;
+        }
         //wait for 4x as long as it would randomly take to reach our node
         //assuming everyone is waiting the same amount of time as this node
         let limit = self.table.len() as u64 * GOSSIP_SLEEP_MILLIS * 4;
-        let purge_set: Vec<PublicKey> = self.alive
+        let dead_ids: Vec<PublicKey> = self.alive
             .iter()
-            .filter_map(|(k, v)| {
-                if *k != self.me && (now - v) > limit {
-                    trace!("purging {:?} {}", &k[..4], v);
-                    Some((*k).clone())
+            .filter_map(|(&k, v)| {
+                if k != self.me && (now - v) > limit {
+                    info!("purge {:?} {}", &k[..4], now - v);
+                    Some(k)
                 } else {
-                    trace!("purge skipped {:?} {}", &k[..4], v);
+                    trace!("purge skipped {:?} {} {}", &k[..4], now - v, limit);
                     None
                 }
             })
             .collect();
-        for p in purge_set.iter() {
-            self.alive.remove(p);
-            self.table.remove(p);
-            self.remote.remove(p);
-            self.local.remove(p);
+        for id in dead_ids.iter() {
+            self.alive.remove(id);
+            self.table.remove(id);
+            self.remote.remove(id);
+            self.local.remove(id);
         }
     }
 
@@ -1054,8 +1061,19 @@ mod tests {
         assert_eq!(rv.0, nxt.gossip_addr);
 
         crdt.purge(now + len * GOSSIP_SLEEP_MILLIS * 4 + 1);
-        let rv = crdt.gossip_request();
-        assert_matches!(rv, Err(Error::CrdtTooSmall));
+        let rv = crdt.gossip_request().unwrap();
+        assert_eq!(rv.0, nxt.gossip_addr);
+
+        let nxt2 = ReplicatedData::new_leader(&"127.0.0.2:1234".parse().unwrap());
+        assert_ne!(me.id, nxt2.id);
+        assert_ne!(nxt.id, nxt2.id);
+        crdt.insert(&nxt2);
+        let len = crdt.table.len() as u64;
+        assert_eq!(3, len);
+        crdt.purge(now + len * GOSSIP_SLEEP_MILLIS * 4 + 1);
+        let rv = crdt.gossip_request().unwrap();
+        assert_eq!(rv.0, nxt.gossip_addr);
+        assert_eq!(2, crdt.table.len());
     }
 
     /// test window requests respond with the right blob, and do not overrun