Do not unban replicas if a primary is available (#843)

Add `unban_replicas_when_all_banned` to control unbanning replicas behavior.

src/config.rs

@@ -315,6 +315,9 @@ pub struct General {
     #[serde(default = "General::default_ban_time")]
     pub ban_time: i64,
 
+    #[serde(default)] // True
+    pub unban_replicas_when_all_banned: bool,
+
     #[serde(default = "General::default_idle_client_in_transaction_timeout")]
     pub idle_client_in_transaction_timeout: u64,
 
@@ -460,6 +463,7 @@ impl Default for General {
             healthcheck_timeout: Self::default_healthcheck_timeout(),
             healthcheck_delay: Self::default_healthcheck_delay(),
             ban_time: Self::default_ban_time(),
+            unban_replicas_when_all_banned: true,
             idle_client_in_transaction_timeout: Self::default_idle_client_in_transaction_timeout(),
             server_lifetime: Self::default_server_lifetime(),
             server_round_robin: Self::default_server_round_robin(),

src/pool.rs

@@ -189,6 +189,9 @@ pub struct PoolSettings {
     // Ban time
     pub ban_time: i64,
 
+    // Should we automatically unban replicas when all are banned?
+    pub unban_replicas_when_all_banned: bool,
+
     // Regex for searching for the sharding key in SQL statements
     pub sharding_key_regex: Option<Regex>,
 
@@ -228,6 +231,7 @@ impl Default for PoolSettings {
             healthcheck_delay: General::default_healthcheck_delay(),
             healthcheck_timeout: General::default_healthcheck_timeout(),
             ban_time: General::default_ban_time(),
+            unban_replicas_when_all_banned: true,
             sharding_key_regex: None,
             shard_id_regex: None,
             regex_search_limit: 1000,
@@ -541,6 +545,9 @@ impl ConnectionPool {
                         healthcheck_delay: config.general.healthcheck_delay,
                         healthcheck_timeout: config.general.healthcheck_timeout,
                         ban_time: config.general.ban_time,
+                        unban_replicas_when_all_banned: config
+                            .general
+                            .unban_replicas_when_all_banned,
                         sharding_key_regex: pool_config
                             .sharding_key_regex
                             .clone()
@@ -946,8 +953,9 @@ impl ConnectionPool {
         let read_guard = self.banlist.read();
         let all_replicas_banned = read_guard[address.shard].len() == replicas_available;
         drop(read_guard);
+        let unban_replicas_when_all_banned = self.settings.clone().unban_replicas_when_all_banned;
 
-        if all_replicas_banned {
+        if all_replicas_banned && unban_replicas_when_all_banned {
             let mut write_guard = self.banlist.write();
             warn!("Unbanning all replicas.");
             write_guard[address.shard].clear();

src/query_router.rs

@@ -1464,6 +1464,7 @@ mod test {
             healthcheck_delay: PoolSettings::default().healthcheck_delay,
             healthcheck_timeout: PoolSettings::default().healthcheck_timeout,
             ban_time: PoolSettings::default().ban_time,
+            unban_replicas_when_all_banned: true,
             sharding_key_regex: None,
             shard_id_regex: None,
             default_shard: crate::config::DefaultShard::Shard(0),
@@ -1542,6 +1543,7 @@ mod test {
             healthcheck_delay: PoolSettings::default().healthcheck_delay,
             healthcheck_timeout: PoolSettings::default().healthcheck_timeout,
             ban_time: PoolSettings::default().ban_time,
+            unban_replicas_when_all_banned: true,
             sharding_key_regex: Some(Regex::new(r"/\* sharding_key: (\d+) \*/").unwrap()),
             shard_id_regex: Some(Regex::new(r"/\* shard_id: (\d+) \*/").unwrap()),
             default_shard: crate::config::DefaultShard::Shard(0),