Add spec doc about unconditional_peer, persistent_peers_max_dial of ADR-050 (#68)

* Add spec doc about unconditional_peer_ids, persistent_peers_max_dial_period of ADR-050

* Add indefinitely dialing condition

spec/p2p/config.md

@@ -26,6 +26,10 @@ These are intended to be trusted persistent peers that can help
 anchor us in the p2p network. The auto-redial uses exponential
 backoff and will give up after a day of trying to connect.
 
+But If `persistent_peers_max_dial_period` is set greater than zero,
+pause between each dial to each persistent peer will not exceed `persistent_peers_max_dial_period`
+during exponential backoff and we keep trying again without giving up
+
 **Note:** If `seeds` and `persistent_peers` intersect,
 the user will be warned that seeds may auto-close connections
 and that the node may not be able to keep the connection persistent.
@@ -36,3 +40,11 @@ and that the node may not be able to keep the connection persistent.
 
 These are IDs of the peers that we do not add to the address book or gossip to
 other peers. They stay private to us.
+
+
+## Unconditional Peers
+
+`--p2p.unconditional_peer_ids “id100000000000000000000000000000000,id200000000000000000000000000000000”`
+
+These are IDs of the peers which are allowed to be connected by both inbound or outbound regardless of 
+`max_num_inbound_peers` or `max_num_outbound_peers` of user's node reached or not.

spec/reactors/pex/pex.md

@@ -31,7 +31,12 @@ On startup, we will also immediately dial the given list of `persistent_peers`,
 and will attempt to maintain persistent connections with them. If the
 connections die, or we fail to dial, we will redial every 5s for a few minutes,
 then switch to an exponential backoff schedule, and after about a day of
-trying, stop dialing the peer.
+trying, stop dialing the peer. This behavior is when `persistent_peers_max_dial_period` is configured to zero.
+
+But If `persistent_peers_max_dial_period` is set greater than zero, terms between each dial to each persistent peer 
+will not exceed `persistent_peers_max_dial_period` during exponential backoff. 
+Therefore, `dial_period` = min(`persistent_peers_max_dial_period`, `exponential_backoff_dial_period`)
+and we keep trying again regardless of `maxAttemptsToDial`
 
 As long as we have less than `MaxNumOutboundPeers`, we periodically request
 additional peers from each of our own and try seeds.
@@ -93,7 +98,8 @@ the selection process happens every `ensurePeersPeriod`, we might not end up
 dialing a peer for much longer than the backoff duration.
 
 If we fail to connect to the peer after 16 tries (with exponential backoff), we
-remove from address book completely.
+remove from address book completely. But for persistent peers, we indefinitely try to
+dial all persistent peers unless `persistent_peers_max_dial_period` is configured to zero
 
 ## Select Peers to Exchange