Iterate archive query alongside task queue.

appengine/logdog/coordinator/backend/backend.go

Index: appengine/logdog/coordinator/backend/backend.go
diff --git a/appengine/logdog/coordinator/backend/backend.go b/appengine/logdog/coordinator/backend/backend.go
index 194bf086dfda90fc4f11749b7b1e03bbe4e5e196..ff1218ce63c04e513f4a650bbcf5bd16b2cd2e11 100644
--- a/appengine/logdog/coordinator/backend/backend.go
+++ b/appengine/logdog/coordinator/backend/backend.go
@@ -11,6 +11,12 @@ import (
 	"github.com/luci/luci-go/server/middleware"
 )
 
+const (
+	// defaultMultiTaskBatchSize is the default value for Backend's
+	// multiTaskBatchSize parameter.
+	defaultMultiTaskBatchSize = 100
+)
+
 // Backend is the base struct for all Backend handlers. It is mostly used to
 // configure testing parameters.
 type Backend struct {
@@ -21,6 +27,13 @@ type Backend struct {
 	s coordinator.Service
 }
 
+func (b *Backend) getMultiTaskBatchSize() int {
+	if v := b.multiTaskBatchSize; v > 0 {
+		return v
+	}
+	return defaultMultiTaskBatchSize
+}
+
 // InstallHandlers installs handlers for the Backend.
 func (b *Backend) InstallHandlers(r *httprouter.Router, h middleware.Base) {
 	r.GET("/archive/cron/terminal", h(gaemiddleware.RequireCron(b.HandleArchiveCron)))