bugfix: reorder paginated queries

storage/client/client.go

@@ -115,15 +115,13 @@ func (c *StorageClient) withTotalCount(ctx context.Context, sql string, args ...
 	if len(args) < 2 {
 		return nil, fmt.Errorf("list queries must have at least two params (limit and offset)")
 	}
-	rows, err := c.db.Query(
-		ctx,
-		sql,
-		args...,
-	)
-	if err != nil {
-		return nil, err
-	}
 
+	// A note on ordering: We query the totalCount before querying for the rows in order to
+	// avoid deadlocks. The row returned by the totalCount query is Scan-ed immediately
+	// and thus the underlying db connection is also released. However, the `rows` are
+	// `Scan`-ed in the calling function, which means that the underlying db connection is
+	// held (and unavailable to other goroutines) in the meantime.
+	limit := args[len(args)-2]
 	args[len(args)-2] = maxTotalCount + 1 // limit
 	if err := c.db.QueryRow(
 		ctx,
@@ -133,6 +131,16 @@ func (c *StorageClient) withTotalCount(ctx context.Context, sql string, args ...
 		return nil, wrapError(err)
 	}
 
+	args[len(args)-2] = limit
+	rows, err := c.db.Query(
+		ctx,
+		sql,
+		args...,
+	)
+	if err != nil {
+		return nil, err
+	}
+
 	clipped := totalCount == maxTotalCount+1
 	if clipped {
 		totalCount = maxTotalCount