fixes

.github/workflows/e2e-api-tests.yaml

@@ -176,26 +176,26 @@ jobs:
           done
 
       - name: Run tests (excluding external DB sync)
-        run: pnpm test run ${{ matrix.freestyle-mode == 'prod' && '--min-workers=1 --max-workers=1' || '' }} --exclude "**/external-db-sync*.test.ts"
+        run: pnpm test run ${{ matrix.freestyle-mode == 'prod' && '--min-workers=1 --max-workers=1' || '' }} --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests (single worker)
-        run: pnpm test run --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm test run --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
 
       - name: Run tests again (excluding external DB sync, attempt 1)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run ${{ matrix.freestyle-mode == 'prod' && '--min-workers=1 --max-workers=1' || '' }} --exclude "**/external-db-sync*.test.ts"
+        run: pnpm test run ${{ matrix.freestyle-mode == 'prod' && '--min-workers=1 --max-workers=1' || '' }} --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests again (single worker, attempt 1)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm test run --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
 
       - name: Run tests again (excluding external DB sync, attempt 2)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run ${{ matrix.freestyle-mode == 'prod' && '--min-workers=1 --max-workers=1' || '' }} --exclude "**/external-db-sync*.test.ts"
+        run: pnpm test run ${{ matrix.freestyle-mode == 'prod' && '--min-workers=1 --max-workers=1' || '' }} --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests again (single worker, attempt 2)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm test run --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
 
       - name: Verify data integrity
         run: pnpm run verify-data-integrity --no-bail

.github/workflows/e2e-custom-base-port-api-tests.yaml

@@ -169,26 +169,26 @@ jobs:
           done
 
       - name: Run tests (excluding external DB sync)
-        run: pnpm test run --exclude "**/external-db-sync*.test.ts"
+        run: pnpm test run --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests (single worker)
-        run: pnpm test run --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm test run --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
 
       - name: Run tests again (excluding external DB sync, attempt 1)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --exclude "**/external-db-sync*.test.ts"
+        run: pnpm test run --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests again (single worker, attempt 1)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm test run --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
 
       - name: Run tests again (excluding external DB sync, attempt 2)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --exclude "**/external-db-sync*.test.ts"
+        run: pnpm test run --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests again (single worker, attempt 2)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm test run --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
 
       - name: Verify data integrity
         run: pnpm run verify-data-integrity --no-bail

.github/workflows/e2e-source-of-truth-api-tests.yaml

@@ -176,26 +176,26 @@ jobs:
           done
 
       - name: Run tests (excluding external DB sync)
-        run: pnpm test run --exclude "**/external-db-sync*.test.ts"
+        run: pnpm test run --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests (single worker)
-        run: pnpm test run --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm test run --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
 
       - name: Run tests again (excluding external DB sync, attempt 1)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --exclude "**/external-db-sync*.test.ts"
+        run: pnpm test run --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests again (single worker, attempt 1)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm test run --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
 
       - name: Run tests again (excluding external DB sync, attempt 2)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --exclude "**/external-db-sync*.test.ts"
+        run: pnpm test run --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests again (single worker, attempt 2)
         if: github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dev'
-        run: pnpm test run --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm test run --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
 
       - name: Verify data integrity
         run: pnpm run verify-data-integrity --no-bail

.github/workflows/restart-dev-and-test-with-custom-base-port.yaml

@@ -41,10 +41,10 @@ jobs:
         run: pnpm run restart-dev-environment
 
       - name: Run tests (excluding external DB sync)
-        run: pnpm run test run --reporter=verbose --exclude "**/external-db-sync*.test.ts"
+        run: pnpm run test run --reporter=verbose --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests (single worker)
-        run: pnpm run test run --reporter=verbose --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm run test run --reporter=verbose --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
       
       - name: Print dev server logs
         run: cat dev-server.log.untracked.txt

.github/workflows/restart-dev-and-test.yaml

@@ -40,10 +40,10 @@ jobs:
         run: pnpm run restart-dev-environment
 
       - name: Run tests (excluding external DB sync)
-        run: pnpm run test run --reporter=verbose --exclude "**/external-db-sync*.test.ts"
+        run: pnpm run test run --reporter=verbose --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests (single worker)
-        run: pnpm run test run --reporter=verbose --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm run test run --reporter=verbose --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync
       
       - name: Print dev server logs
         run: cat dev-server.log.untracked.txt

.github/workflows/setup-tests-with-custom-base-port.yaml

@@ -50,7 +50,7 @@ jobs:
           wait-for: 120s
           log-output-if: true
       - name: Run tests (excluding external DB sync)
-        run: pnpm run test run --reporter=verbose --exclude "**/external-db-sync*.test.ts"
+        run: pnpm run test run --reporter=verbose --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests (single worker)
-        run: pnpm run test run --reporter=verbose --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm run test run --reporter=verbose --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync

.github/workflows/setup-tests.yaml

@@ -48,7 +48,7 @@ jobs:
           wait-for: 120s
           log-output-if: true
       - name: Run tests (excluding external DB sync)
-        run: pnpm run test run --reporter=verbose --exclude "**/external-db-sync*.test.ts"
+        run: pnpm run test run --reporter=verbose --exclude "apps/e2e/tests/backend/endpoints/api/v1/external-db-sync"
 
       - name: Run external DB sync tests (single worker)
-        run: pnpm run test run --reporter=verbose --min-workers=1 --max-workers=1 **/external-db-sync*.test.ts
+        run: pnpm run test run --reporter=verbose --min-workers=1 --max-workers=1 apps/e2e/tests/backend/endpoints/api/v1/external-db-sync

apps/backend/prisma/migrations/20251125030551_external_db_sync/migration.sql

@@ -23,6 +23,14 @@ CREATE UNIQUE INDEX  "ContactChannel_sequenceId_key" ON "ContactChannel"("sequen
 -- SPLIT_STATEMENT_SENTINEL
 CREATE UNIQUE INDEX  "ProjectUser_sequenceId_key" ON "ProjectUser"("sequenceId");
 
+-- SPLIT_STATEMENT_SENTINEL
+-- Creates composite indexes on (tenancyId, sequenceId) for efficient sync-engine queries.
+-- These allow fast lookups of rows by tenant ordered by sequence number.
+CREATE INDEX "ProjectUser_tenancyId_sequenceId_idx" ON "ProjectUser"("tenancyId", "sequenceId");
+
+-- SPLIT_STATEMENT_SENTINEL
+CREATE INDEX "ContactChannel_tenancyId_sequenceId_idx" ON "ContactChannel"("tenancyId", "sequenceId");
+
 -- SPLIT_STATEMENT_SENTINEL
 -- Creates OutgoingRequest table to queue sync requests to external databases.
 -- Each request stores the QStash options for making HTTP requests and tracks when fulfillment started.
@@ -81,14 +89,15 @@ ALTER TABLE "ContactChannel" ADD COLUMN "shouldUpdateSequenceId" BOOLEAN NOT NUL
 ALTER TABLE "DeletedRow" ADD COLUMN "shouldUpdateSequenceId" BOOLEAN NOT NULL DEFAULT TRUE;
 
 -- SPLIT_STATEMENT_SENTINEL
--- Creates partial indexes on shouldUpdateSequenceId to quickly find rows that need updates.
-CREATE INDEX "ProjectUser_shouldUpdateSequenceId_idx" ON "ProjectUser"("shouldUpdateSequenceId") WHERE "shouldUpdateSequenceId" = TRUE;
+-- Creates partial indexes on (shouldUpdateSequenceId, tenancyId) to quickly find rows that need updates
+-- and support ORDER BY tenancyId for less fragmented updates.
+CREATE INDEX "ProjectUser_shouldUpdateSequenceId_idx" ON "ProjectUser"("shouldUpdateSequenceId", "tenancyId") WHERE "shouldUpdateSequenceId" = TRUE;
 
 -- SPLIT_STATEMENT_SENTINEL
-CREATE INDEX "ContactChannel_shouldUpdateSequenceId_idx" ON "ContactChannel"("shouldUpdateSequenceId") WHERE "shouldUpdateSequenceId" = TRUE;
+CREATE INDEX "ContactChannel_shouldUpdateSequenceId_idx" ON "ContactChannel"("shouldUpdateSequenceId", "tenancyId") WHERE "shouldUpdateSequenceId" = TRUE;
 
 -- SPLIT_STATEMENT_SENTINEL
-CREATE INDEX "DeletedRow_shouldUpdateSequenceId_idx" ON "DeletedRow"("shouldUpdateSequenceId") WHERE "shouldUpdateSequenceId" = TRUE;
+CREATE INDEX "DeletedRow_shouldUpdateSequenceId_idx" ON "DeletedRow"("shouldUpdateSequenceId", "tenancyId") WHERE "shouldUpdateSequenceId" = TRUE;
 
 -- SPLIT_STATEMENT_SENTINEL
 -- SINGLE_STATEMENT_SENTINEL

apps/backend/prisma/schema.prisma

@@ -225,6 +225,7 @@ model ProjectUser {
   @@index([tenancyId, displayName(sort: Desc)], name: "ProjectUser_displayName_desc")
   @@index([tenancyId, createdAt(sort: Asc)], name: "ProjectUser_createdAt_asc")
   @@index([tenancyId, createdAt(sort: Desc)], name: "ProjectUser_createdAt_desc")
+  @@index([tenancyId, sequenceId], name: "ProjectUser_tenancyId_sequenceId_idx")
   // Partial index for external db sync backfill lives in migration SQL.
 }
 
@@ -290,6 +291,7 @@ model ContactChannel {
   @@unique([tenancyId, projectUserId, type, value])
   // only one contact channel per project with the same value and type can be used for auth
   @@unique([tenancyId, type, value, usedForAuth])
+  @@index([tenancyId, sequenceId], name: "ContactChannel_tenancyId_sequenceId_idx")
   // Partial index for external db sync backfill lives in migration SQL (WHERE shouldUpdateSequenceId = TRUE).
 }
 

apps/backend/src/app/api/latest/internal/external-db-sync/sequencer/route.ts

@@ -1,4 +1,4 @@
-import { getPrismaClientForTenancy, globalPrismaClient, type PrismaClientTransaction } from "@/prisma-client";
+import { globalPrismaClient } from "@/prisma-client";
 import { createSmartRouteHandler } from "@/route-handlers/smart-route-handler";
 import {
   yupBoolean,
@@ -10,10 +10,8 @@ import {
 import { getEnvVariable } from "@stackframe/stack-shared/dist/utils/env";
 import { captureError, StatusError } from "@stackframe/stack-shared/dist/utils/errors";
 import { wait } from "@stackframe/stack-shared/dist/utils/promises";
-import { getTenancy, type Tenancy } from "@/lib/tenancies";
-import { enqueueExternalDbSync } from "@/lib/external-db-sync-queue";
+import { enqueueExternalDbSyncBatch } from "@/lib/external-db-sync-queue";
 
-const UUID_REGEX = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
 const DEFAULT_MAX_DURATION_MS = 3 * 60 * 1000;
 
 function parseMaxDurationMs(value: string | undefined): number {
@@ -32,11 +30,6 @@ function parseStopWhenIdle(value: string | undefined): boolean {
   throw new StatusError(400, "stopWhenIdle must be 'true' or 'false'");
 }
 
-function assertUuid(value: unknown, label: string): asserts value is string {
-  if (typeof value !== "string" || value.trim().length === 0 || !UUID_REGEX.test(value)) {
-    throw new StatusError(500, `${label} must be a valid UUID. Received: ${JSON.stringify(value)}`);
-  }
-}
 
 // Assigns sequence IDs to rows that need them and queues sync requests for affected tenants.
 // Processes up to 1000 rows at a time from each table.
@@ -48,6 +41,7 @@ async function backfillSequenceIds(): Promise<boolean> {
       FROM "ProjectUser"
       WHERE "shouldUpdateSequenceId" = TRUE
       OR "sequenceId" IS NULL
+      ORDER BY "tenancyId"
       LIMIT 1000
       FOR UPDATE SKIP LOCKED
     ),
@@ -63,12 +57,9 @@ async function backfillSequenceIds(): Promise<boolean> {
     SELECT DISTINCT "tenancyId" FROM updated_rows
   `;
 
-  // Enqueue sync for each affected tenant
-  for (const { tenancyId } of projectUserTenants) {
-    assertUuid(tenancyId, "projectUserTenants.tenancyId");
-    await enqueueExternalDbSync(tenancyId);
-  }
+  // Enqueue sync for all affected tenants in a single batch query
   if (projectUserTenants.length > 0) {
+    await enqueueExternalDbSyncBatch(projectUserTenants.map(t => t.tenancyId));
     didUpdate = true;
   }
 
@@ -78,6 +69,7 @@ async function backfillSequenceIds(): Promise<boolean> {
       FROM "ContactChannel"
       WHERE "shouldUpdateSequenceId" = TRUE
       OR "sequenceId" IS NULL
+      ORDER BY "tenancyId"
       LIMIT 1000
       FOR UPDATE SKIP LOCKED
     ),
@@ -94,11 +86,8 @@ async function backfillSequenceIds(): Promise<boolean> {
     SELECT DISTINCT "tenancyId" FROM updated_rows
   `;
 
-  for (const { tenancyId } of contactChannelTenants) {
-    assertUuid(tenancyId, "contactChannelTenants.tenancyId");
-    await enqueueExternalDbSync(tenancyId);
-  }
   if (contactChannelTenants.length > 0) {
+    await enqueueExternalDbSyncBatch(contactChannelTenants.map(t => t.tenancyId));
     didUpdate = true;
   }
 
@@ -108,6 +97,7 @@ async function backfillSequenceIds(): Promise<boolean> {
       FROM "DeletedRow"
       WHERE "shouldUpdateSequenceId" = TRUE
       OR "sequenceId" IS NULL
+      ORDER BY "tenancyId"
       LIMIT 1000
       FOR UPDATE SKIP LOCKED
     ),
@@ -122,125 +112,17 @@ async function backfillSequenceIds(): Promise<boolean> {
     SELECT DISTINCT "tenancyId" FROM updated_rows
   `;
 
-  for (const { tenancyId } of deletedRowTenants) {
-    assertUuid(tenancyId, "deletedRowTenants.tenancyId");
-    await enqueueExternalDbSync(tenancyId);
-  }
   if (deletedRowTenants.length > 0) {
+    await enqueueExternalDbSyncBatch(deletedRowTenants.map(t => t.tenancyId));
     didUpdate = true;
   }
 
   return didUpdate;
 }
 
-async function backfillSequenceIdsForTenancy(prisma: PrismaClientTransaction, tenancyId: string): Promise<boolean> {
-  assertUuid(tenancyId, "tenancyId");
-  let didUpdate = false;
-
-  const projectUserRows = await prisma.$queryRaw<{ tenancyId: string }[]>`
-    WITH rows_to_update AS (
-      SELECT "tenancyId", "projectUserId"
-      FROM "ProjectUser"
-      WHERE ("shouldUpdateSequenceId" = TRUE OR "sequenceId" IS NULL)
-      AND "tenancyId" = ${tenancyId}::uuid
-      LIMIT 1000
-      FOR UPDATE SKIP LOCKED
-    ),
-    updated_rows AS (
-      UPDATE "ProjectUser" pu
-      SET "sequenceId" = nextval('global_seq_id'),
-          "shouldUpdateSequenceId" = FALSE
-      FROM rows_to_update r
-      WHERE pu."tenancyId"     = r."tenancyId"
-        AND pu."projectUserId" = r."projectUserId"
-      RETURNING pu."tenancyId"
-    )
-    SELECT DISTINCT "tenancyId" FROM updated_rows
-  `;
-  if (projectUserRows.length > 0) {
-    didUpdate = true;
-  }
-
-  const contactChannelRows = await prisma.$queryRaw<{ tenancyId: string }[]>`
-    WITH rows_to_update AS (
-      SELECT "tenancyId", "projectUserId", "id"
-      FROM "ContactChannel"
-      WHERE ("shouldUpdateSequenceId" = TRUE OR "sequenceId" IS NULL)
-      AND "tenancyId" = ${tenancyId}::uuid
-      LIMIT 1000
-      FOR UPDATE SKIP LOCKED
-    ),
-    updated_rows AS (
-      UPDATE "ContactChannel" cc
-      SET "sequenceId" = nextval('global_seq_id'),
-          "shouldUpdateSequenceId" = FALSE
-      FROM rows_to_update r
-      WHERE cc."tenancyId"     = r."tenancyId"
-        AND cc."projectUserId" = r."projectUserId"
-        AND cc."id"            = r."id"
-      RETURNING cc."tenancyId"
-    )
-    SELECT DISTINCT "tenancyId" FROM updated_rows
-  `;
-  if (contactChannelRows.length > 0) {
-    didUpdate = true;
-  }
-
-  const deletedRowRows = await prisma.$queryRaw<{ tenancyId: string }[]>`
-    WITH rows_to_update AS (
-      SELECT "id", "tenancyId"
-      FROM "DeletedRow"
-      WHERE ("shouldUpdateSequenceId" = TRUE OR "sequenceId" IS NULL)
-      AND "tenancyId" = ${tenancyId}::uuid
-      LIMIT 1000
-      FOR UPDATE SKIP LOCKED
-    ),
-    updated_rows AS (
-      UPDATE "DeletedRow" dr
-      SET "sequenceId" = nextval('global_seq_id'),
-          "shouldUpdateSequenceId" = FALSE
-      FROM rows_to_update r
-      WHERE dr."id" = r."id"
-      RETURNING dr."tenancyId"
-    )
-    SELECT DISTINCT "tenancyId" FROM updated_rows
-  `;
-  if (deletedRowRows.length > 0) {
-    didUpdate = true;
-  }
-
-  return didUpdate;
-}
-
-async function getNonHostedTenancies(): Promise<Tenancy[]> {
-  const tenancyIds = await globalPrismaClient.tenancy.findMany({
-    select: { id: true },
-  });
-
-  const tenancies: Tenancy[] = [];
-  for (const { id } of tenancyIds) {
-    const tenancy = await getTenancy(id);
-    if (!tenancy) continue;
-    if (tenancy.config.sourceOfTruth.type !== "hosted") {
-      tenancies.push(tenancy);
-    }
-  }
-
-  return tenancies;
-}
-
-async function backfillSequenceIdsForNonHostedTenancies(tenancies: Tenancy[]): Promise<boolean> {
-  let didUpdate = false;
-  for (const tenancy of tenancies) {
-    const prisma = await getPrismaClientForTenancy(tenancy);
-    const tenancyDidUpdate = await backfillSequenceIdsForTenancy(prisma, tenancy.id);
-    if (tenancyDidUpdate) {
-      await enqueueExternalDbSync(tenancy.id);
-      didUpdate = true;
-    }
-  }
-  return didUpdate;
-}
+// TODO: If we ever need to support non-hosted source-of-truth tenancies again,
+// we'll need to implement a scalable way to iterate over them (pagination, etc.)
+// instead of loading all tenancies into memory at once.
 
 export const GET = createSmartRouteHandler({
   metadata: {
@@ -275,10 +157,6 @@ export const GET = createSmartRouteHandler({
       throw new StatusError(401, "Unauthorized");
     }
 
-    let nonHostedTenancies = await getNonHostedTenancies();
-    let lastTenancyRefreshMs = performance.now();
-    const tenancyRefreshIntervalMs = 5_000;
-
     const startTime = performance.now();
     const maxDurationMs = parseMaxDurationMs(query.maxDurationMs);
     const stopWhenIdle = parseStopWhenIdle(query.stopWhenIdle);
@@ -288,13 +166,8 @@ export const GET = createSmartRouteHandler({
 
     while (performance.now() - startTime < maxDurationMs) {
       try {
-        if (performance.now() - lastTenancyRefreshMs >= tenancyRefreshIntervalMs) {
-          nonHostedTenancies = await getNonHostedTenancies();
-          lastTenancyRefreshMs = performance.now();
-        }
-        const didUpdateHosted = await backfillSequenceIds();
-        const didUpdateNonHosted = await backfillSequenceIdsForNonHostedTenancies(nonHostedTenancies);
-        if (stopWhenIdle && !didUpdateHosted && !didUpdateNonHosted) {
+        const didUpdate = await backfillSequenceIds();
+        if (stopWhenIdle && !didUpdate) {
           break;
         }
       } catch (error) {

apps/backend/src/app/api/latest/internal/external-db-sync/sync-engine/route.tsx

@@ -32,8 +32,8 @@ export const POST = createSmartRouteHandler({
 
     const tenancy = await getTenancy(tenancyId);
     if (!tenancy) {
-console.warn(`[sync-engine] Tenancy ${tenancyId} in queue but not found.`);
-throw new StatusError(404, `Tenancy ${tenancyId} not found.`);
+      console.warn(`[sync-engine] Tenancy ${tenancyId} in queue but not found, assuming it was deleted.`);
+      throw new StatusError(400, `Tenancy ${tenancyId} not found.`);
     }
 
     await syncExternalDatabases(tenancy);

apps/backend/src/lib/external-db-sync-queue.ts

@@ -12,6 +12,19 @@ function assertUuid(value: unknown, label: string): asserts value is string {
 // Queues a sync request for a specific tenant if one isn't already pending.
 export async function enqueueExternalDbSync(tenancyId: string): Promise<void> {
   assertUuid(tenancyId, "tenancyId");
+  await enqueueExternalDbSyncBatch([tenancyId]);
+}
+
+// Queues sync requests for multiple tenants in a single query.
+// Only inserts for tenants that don't already have a pending request.
+export async function enqueueExternalDbSyncBatch(tenancyIds: string[]): Promise<void> {
+  if (tenancyIds.length === 0) return;
+
+  for (const id of tenancyIds) {
+    assertUuid(id, "tenancyId");
+  }
+
+  // Use unnest to pass array of UUIDs and insert all in one query
   await globalPrismaClient.$executeRaw`
     INSERT INTO "OutgoingRequest" ("id", "createdAt", "qstashOptions", "startedFulfillingAt")
     SELECT
@@ -19,14 +32,15 @@ export async function enqueueExternalDbSync(tenancyId: string): Promise<void> {
       NOW(),
       json_build_object(
         'url',  '/api/latest/internal/external-db-sync/sync-engine',
-        'body', json_build_object('tenancyId', ${tenancyId}::uuid)
+        'body', json_build_object('tenancyId', t.tenancy_id)
       ),
       NULL
+    FROM unnest(${tenancyIds}::uuid[]) AS t(tenancy_id)
     WHERE NOT EXISTS (
       SELECT 1
       FROM "OutgoingRequest"
       WHERE "startedFulfillingAt" IS NULL
-        AND ("qstashOptions"->'body'->>'tenancyId')::uuid = ${tenancyId}::uuid
+        AND ("qstashOptions"->'body'->>'tenancyId')::uuid = t.tenancy_id
     )
   `;
 }