Merge bitcoin/bitcoin#22576: doc: Update high-level addrman description

036d7eadf5dd0e06e0734a5d78dbe28f4bfaa07f doc: Correct description of CAddrMan::Create() (Amiti Uttarwar)
318176aff1ded36d1fbc5977f288ac3bac1d8712 doc: Update high-level addrman description (Martin Zumsande)

Pull request description:

  The high-level description of `addrman` has outdated information with respect to the eviction behavior, both for the New and Tried tables (at least since #5941) - this has confused me in the past.

  This PR corrects this and also adds basic info about the bucket size and position.

ACKs for top commit:
  amitiuttarwar:
    reACK 036d7eadf5dd0e06e0734a5d78dbe28f4bfaa07f
  jnewbery:
    ACK 036d7eadf5dd0e06e0734a5d78dbe28f4bfaa07f

Tree-SHA512: 3f0635d765f5e580a1fae31187742a833cef66ef2286d40eeb28f2253521260038e16e5f1a65741464a2ddfdbeb5c0f1bc38bf73841e600639033d59c3c534e4

1 files changed, 12 insertions, 9 deletions

diff --git a/src/addrman.h b/src/addrman.h
index 4d8d05a99a..736d9783e6 100644
--- a/src/addrman.h
+++ b/src/addrman.h
@@ -104,19 +104,23 @@ public:
  *  * Make sure no (localized) attacker can fill the entire table with his nodes/addresses.
  *
  * To that end:
- *  * Addresses are organized into buckets.
- *    * Addresses that have not yet been tried go into 1024 "new" buckets.
- *      * Based on the address range (/16 for IPv4) of the source of information, 64 buckets are selected at random.
+ *  * Addresses are organized into buckets that can each store up to 64 entries.
+ *    * Addresses to which our node has not successfully connected go into 1024 "new" buckets.
+ *      * Based on the address range (/16 for IPv4) of the source of information, or if an asmap is provided,
+ *        the AS it belongs to (for IPv4/IPv6), 64 buckets are selected at random.
  *      * The actual bucket is chosen from one of these, based on the range in which the address itself is located.
+ *      * The position in the bucket is chosen based on the full address.
  *      * One single address can occur in up to 8 different buckets to increase selection chances for addresses that
  *        are seen frequently. The chance for increasing this multiplicity decreases exponentially.
- *      * When adding a new address to a full bucket, a randomly chosen entry (with a bias favoring less recently seen
- *        ones) is removed from it first.
+ *      * When adding a new address to an occupied position of a bucket, it will not replace the existing entry
+ *        unless that address is also stored in another bucket or it doesn't meet one of several quality criteria
+ *        (see IsTerrible for exact criteria).
  *    * Addresses of nodes that are known to be accessible go into 256 "tried" buckets.
  *      * Each address range selects at random 8 of these buckets.
  *      * The actual bucket is chosen from one of these, based on the full address.
- *      * When adding a new good address to a full bucket, a randomly chosen entry (with a bias favoring less recently
- *        tried ones) is evicted from it, back to the "new" buckets.
+ *      * When adding a new good address to an occupied position of a bucket, a FEELER connection to the
+ *        old address is attempted. The old entry is only replaced and moved back to the "new" buckets if this
+ *        attempt was unsuccessful.
  *    * Bucket selection is based on cryptographic hashing, using a randomly-generated 256-bit key, which should not
  *      be observable by adversaries.
  *    * Several indexes are kept for high performance. Defining DEBUG_ADDRMAN will introduce frequent (and expensive)
@@ -696,8 +700,7 @@ private:
     //! Find an entry.
     CAddrInfo* Find(const CNetAddr& addr, int *pnId = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
-    //! find an entry, creating it if necessary.
-    //! nTime and nServices of the found node are updated, if necessary.
+    //! Create a new entry and add it to the internal data structures mapInfo, mapAddr and vRandom.
     CAddrInfo* Create(const CAddress &addr, const CNetAddr &addrSource, int *pnId = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
     //! Swap two elements in vRandom.