Fix: try to improve performance of last query

internal/postgres/operation/storage.go

@@ -122,32 +122,45 @@ func (storage *Storage) GetByAccount(acc account.Account, size uint64, filters m
 
 // Last - get last operation by `filters` with not empty deffated_storage
 func (storage *Storage) Last(filters map[string]interface{}, lastID int64) (operation.Operation, error) {
-	query := storage.DB.Model((*operation.Operation)(nil)).Where("deffated_storage is not null").OrderExpr("operation.id desc")
-
-	for key, value := range filters {
-		query.Where("? = ?", pg.Ident(key), value)
-	}
+	var (
+		current = time.Date(time.Now().Year(), 1, 1, 0, 0, 0, 0, time.UTC)
+	)
+
+	for current.Year() < 2018 {
+		query := storage.DB.Model((*operation.Operation)(nil)).
+			Where("deffated_storage is not null").
+			Where("timestamp >= ?", current).
+			Where("timestamp < ?", current.AddDate(1, 0, 0)).
+			OrderExpr("operation.id desc")
+
+		for key, value := range filters {
+			query.Where("? = ?", pg.Ident(key), value)
+		}
 
-	if lastID > 0 {
-		query.Where("operation.id < ?", lastID)
-	}
+		if lastID > 0 {
+			query.Where("operation.id < ?", lastID)
+		}
 
-	query.Limit(2) // It's a hack to avoid postgres "optimization". Limit = 1 is extremely slow.
+		query.Limit(2) // It's a hack to avoid postgres "optimization". Limit = 1 is extremely slow.
+
+		var ops []operation.Operation
+		if err := storage.DB.Model().TableExpr("(?) as operation", query).
+			ColumnExpr("operation.*").
+			ColumnExpr("source.address as source__address").
+			ColumnExpr("destination.address as destination__address").
+			Join("LEFT JOIN accounts as source ON source.id = operation.source_id").
+			Join("LEFT JOIN accounts as destination ON destination.id = operation.destination_id").
+			Select(&ops); err != nil {
+			return operation.Operation{}, err
+		}
+		if len(ops) > 0 {
+			return ops[0], nil
+		}
 
-	var ops []operation.Operation
-	if err := storage.DB.Model().TableExpr("(?) as operation", query).
-		ColumnExpr("operation.*").
-		ColumnExpr("source.address as source__address").
-		ColumnExpr("destination.address as destination__address").
-		Join("LEFT JOIN accounts as source ON source.id = operation.source_id").
-		Join("LEFT JOIN accounts as destination ON destination.id = operation.destination_id").
-		Select(&ops); err != nil {
-		return operation.Operation{}, err
-	}
-	if len(ops) == 0 {
-		return operation.Operation{}, pg.ErrNoRows
+		current = current.AddDate(-1, 0, 0)
 	}
-	return ops[0], nil
+
+	return operation.Operation{}, pg.ErrNoRows
 }
 
 // Get -