[gitpod-db] Don't consider garbage-collected prebuilds as potential b…

…ases for incremental prebuilds

components/gitpod-db/src/typeorm/workspace-db-impl.ts

@@ -754,6 +754,7 @@ export abstract class AbstractTypeORMWorkspaceDBImpl implements WorkspaceDB {
         query = query.orderBy("pws.creationTime", "DESC");
         query = query.innerJoinAndMapOne("pws.workspace", DBWorkspace, "ws", "pws.buildWorkspaceId = ws.id");
         query = query.andWhere("ws.deleted = false");
+        query = query.andWhere("ws.contentDeletedTime = ''");
 
         const res = await query.getMany();
         return res.map((r) => {

components/server/ee/src/workspace/workspace-factory.ts

@@ -106,6 +106,8 @@ export class WorkspaceFactoryEE extends WorkspaceFactory {
             // Walk back the last prebuilds and check if they are valid ancestor.
             let ws;
             if (context.commitHistory && context.commitHistory.length > 0) {
+                // Note: This query returns only not-garbage-collected prebuilds in order to reduce cardinality
+                // (e.g., at the time of writing, the Gitpod repository has 16K+ prebuilds, but only ~300 not-garbage-collected)
                 const recentPrebuilds = await this.db
                     .trace({ span })
                     .findPrebuildsWithWorkpace(commitContext.repository.cloneUrl);