delegations: remove delegations with 0 shares

.changelog/711.feature.md

@@ -0,0 +1 @@
+delegations: delete delegations with 0 shares

analyzer/consensus/consensus.go

@@ -921,6 +921,33 @@ func (m *processor) queueEscrows(batch *storage.QueryBatch, data *stakingData) e
 			e.Owner.String(),
 			e.ActiveShares.String(),
 		)
+		// Ideally this would be merged with the ConsensusDebondingStartDelegationsUpdate query above,
+		// something like:
+		//
+		// ```
+		//   WITH updated AS (
+		//       UPDATE chain.delegations
+		//       SET shares = shares - $3
+		//       WHERE delegatee = $1 AND delegator = $2
+		//       RETURNING delegatee, delegator, shares
+		//   )
+		//
+		//   -- Delete the delegation if the shares are now 0.
+		//   DELETE FROM chain.delegations
+		//     USING updated
+		//     WHERE chain.delegations.delegatee = updated.delegatee
+		//       AND chain.delegations.delegator = updated.delegator
+		//       AND updated.shares = 0`
+		// ```
+		//
+		// but it is not possible since CTE's cannot handle updating the same row twice:
+		// https://www.postgresql.org/docs/current/queries-with.html#QUERIES-WITH-MODIFYING
+		//
+		// So we need to issue a separate query to delete if zero.
+		batch.Queue(queries.ConsensusDelegationDeleteIfZeroShares,
+			e.Escrow.String(),
+			e.Owner.String(),
+		)
 		batch.Queue(queries.ConsensusDebondingStartDebondingDelegationsInsert,
 			e.Escrow.String(),
 			e.Owner.String(),

analyzer/queries/queries.go

@@ -338,15 +338,6 @@ var (
         escrow_balance_active = chain.accounts.escrow_balance_active + $2,
         escrow_total_shares_active = chain.accounts.escrow_total_shares_active + $3`
 
-	ConsensusAddDelegationsUpsertReplace = `
-    INSERT INTO chain.delegations
-      (delegatee, delegator, shares)
-    VALUES
-      ($1, $2, $3)
-    ON CONFLICT (delegatee, delegator) DO UPDATE
-    SET
-      shares = excluded.shares`
-
 	ConsensusAddDelegationsUpsert = `
     INSERT INTO chain.delegations (delegatee, delegator, shares)
       VALUES ($1, $2, $3)
@@ -381,6 +372,10 @@ var (
       SET shares = shares - $3
         WHERE delegatee = $1 AND delegator = $2`
 
+	ConsensusDelegationDeleteIfZeroShares = `
+    DELETE FROM chain.delegations
+      WHERE delegatee = $1 AND delegator = $2 AND shares = 0`
+
 	ConsensusDebondingStartDebondingDelegationsInsert = `
     INSERT INTO chain.debonding_delegations (delegatee, delegator, shares, debond_end)
       VALUES ($1, $2, $3, $4)`

storage/migrations/17_delegations_zero_shares.up.sql

@@ -0,0 +1,10 @@
+BEGIN;
+
+-- Starting with this commit, the delegations with zero shares will get cleaned up
+-- at the debond start time (on reclaim escrow transaction). Here we clean up the
+-- delegations that were already debonded and have 0 shares at the time of this
+-- deployment.
+DELETE FROM chain.delegations
+    WHERE shares = 0;
+
+COMMIT;