sqldb/sqlc: add zombie index table

Note that this table will only contain entries for channels that we have
deleted from the `channels` table which is why we cannot use foreign
keys. Similarly, we may no longer have node entries for the nodes in the
table.

sqldb/sqlc/migrations/000007_graph.down.sql

@@ -25,4 +25,6 @@ DROP TABLE IF EXISTS source_nodes;
 DROP TABLE IF EXISTS node_addresses;
 DROP TABLE IF EXISTS node_features;
 DROP TABLE IF EXISTS node_extra_types;
-DROP TABLE IF EXISTS nodes;
+DROP TABLE IF EXISTS nodes;
+DROP TABLE IF EXISTS channel_policy_extra_types;
+DROP TABLE IF EXISTS zombie_channels;

sqldb/sqlc/migrations/000007_graph.up.sql

@@ -292,3 +292,31 @@ CREATE TABLE IF NOT EXISTS channel_policy_extra_types (
 CREATE UNIQUE INDEX IF NOT EXISTS channel_policy_extra_types_unique ON channel_policy_extra_types (
     type, channel_policy_id
 );
+
+/* ─────────────────────────────────────────────
+   Other graph related tables
+   ─────────────────────────────────────────────
+*/
+
+CREATE TABLE IF NOT EXISTS zombie_channels (
+    -- The channel id (short channel id) of the channel.
+    -- NOTE: we don't use a foreign key here to the `channels`
+    -- table since we may delete the channel record once it
+    -- is marked as a zombie.
+    scid BLOB NOT NULL,
+
+    -- The protocol version that this node was gossiped on.
+    version SMALLINT NOT NULL,
+
+    -- The public key of the node 1 node of the channel. If
+    -- this is not null, it means an update from this node
+    -- will be able to resurrect the channel.
+    node_key_1 BLOB,
+
+    -- The public key of the node 2 node of the channel. If
+    -- this is not null, it means an update from this node
+    -- will be able to resurrect the channel.
+    node_key_2 BLOB
+);
+CREATE UNIQUE INDEX IF NOT EXISTS zombie_channels_channel_id_version_idx
+    ON zombie_channels(scid, version);

sqldb/sqlc/models.go

@@ -184,3 +184,10 @@ type NodeFeature struct {
 type SourceNode struct {
 	NodeID int64
 }
+
+type ZombieChannel struct {
+	Scid     []byte
+	Version  int16
+	NodeKey1 []byte
+	NodeKey2 []byte
+}