Data Connect Emulator v3.0.2 Transaction Mutation Hang

When doing a Data Connect transaction mutation the request hangs.

This happens on firebase-tools version 15.3.0
- 15.2.0 is stable.
Specifically, I believe it comes from the Update Data Connect Emulator to 3.0.2 PR (Data Connect Emulator release v3.0.2 #9738).
Also tested on a NEW flutter and firebase project with the same results.
This also happens on version 15.3.1 but that looks like it was just MCP updates.

[REQUIRED] Environment info

firebase-tools: 15.3.0, 15.3.1

Platform: Windows 11 Pro

Application SDK: Flutter

[REQUIRED] Test case

Tested with a simple transaction mutation.

Schema:

type Test @table(name: "test_tests") {
  id: Int64!
  message: String
}

Mutation Transaction:

mutation TransactionTest(
  $id: Int64!
  $message: String!
  $updateMessage: String!
) @transaction @auth(level: PUBLIC) {
  query
    @redact
    @check(
      expr: "response.query.existingTest == null"
      message: "Test record already exists!"
    ) {
    existingTest: test(first: { where: { id: { eq: $id } } }) {
      id
      message
    }
  }

  insert: test_insert(data: { id: $id, message: $message })

  update: test_update(
    first: { where: { id: { eq_expr: "response.insert.id" } } }
    data: { message: $updateMessage }
  )
}

[REQUIRED] Steps to reproduce

Install firebase-tools 15.3.0
Copy in the simple transaction mutation provided
Run firebase emulators:start --debug
Trigger a Data Connect transaction mutation that writes to the DB
Request hangs indefinitely
Restart application, emulator crashes

NOTE: If you downgrade to firebase-tools 15.2.0 it works.

[REQUIRED] Expected behavior

Transaction mutation completes and doesn't infinitely hang.

[REQUIRED] Actual behavior

I suspect this excerpt from the full log result below:

Error: Unexpected initial message
    at _class5.handleClientMessage (C:\Users\user\AppData\Roaming\npm\node_modules\firebase-tools\node_modules\pg-gateway\dist\chunk-FCOSUQFU.cjs:1:212007)
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
    at async _class5.processData (C:\Users\user\AppData\Roaming\npm\node_modules\firebase-tools\node_modules\pg-gateway\dist\chunk-FCOSUQFU.cjs:1:211063)
    at async _class5.init (C:\Users\user\AppData\Roaming\npm\node_modules\firebase-tools\node_modules\pg-gateway\dist\chunk-FCOSUQFU.cjs:1:209869)
!!  dataconnect: Postgres threw an unexpected error, shutting down the Data Connect emulator: AbortError: The operation was aborted {"metadata":{"emulator":{"name":"dataconnect"},"message":"Postgres threw an unexpected error, shutting down the Data Connect emulator: AbortError: The operation was aborted"}}

Log after running the transaction.

[2026-01-16T19:12:24.688Z] I0116 13:12:24.688136   47764 prepare.go:110] [operation "TransactionTest"] preparePlan succeeded
I0116 13:12:24.688136   47764 prepare.go:101] [operation "TransactionTest"] DBStats beforePrepare: sql.DBStats{MaxOpenConnections:1, OpenConnections:1, InUse:0, Idle:1, WaitCount:0, WaitDuration:0, MaxIdleClosed:0, MaxIdleTimeClosed:0, MaxLifetimeClosed:0}, afterPrepare: sql.DBStats{MaxOpenConnections:1, OpenConnections:1, InUse:0, Idle:1, WaitCount:0, WaitDuration:0, MaxIdleClosed:0, MaxIdleTimeClosed:0, MaxLifetimeClosed:0}
 {"metadata":{"emulator":{"name":"dataconnect"},"message":"I0116 13:12:24.688136   47764 prepare.go:110] [operation \"TransactionTest\"] preparePlan succeeded\nI0116 13:12:24.688136   47764 prepare.go:101] [operation \"TransactionTest\"] DBStats beforePrepare: sql.DBStats{MaxOpenConnections:1, OpenConnections:1, InUse:0, Idle:1, WaitCount:0, WaitDuration:0, MaxIdleClosed:0, MaxIdleTimeClosed:0, MaxLifetimeClosed:0}, afterPrepare: sql.DBStats{MaxOpenConnections:1, OpenConnections:1, InUse:0, Idle:1, WaitCount:0, WaitDuration:0, MaxIdleClosed:0, MaxIdleTimeClosed:0, MaxLifetimeClosed:0}\n"}}

Same log session, but after I reloaded the app because of the hang ~5 minutes later; emulator crashes

runQuery DEALLOCATE ALL [] undefined
[2026-01-16T19:18:08.302Z] Postgres client disconnected
[2026-01-16T19:18:08.302Z] E0116 13:18:08.299339   47764 execute.go:47] Database ping failed: input:
 after 5m43.610117s
stats before: sql.DBStats{MaxOpenConnections:1, OpenConnections:1, InUse:1, Idle:0, WaitCount:0, WaitDuration:0, MaxIdleClosed:0, MaxIdleTimeClosed:0, MaxLifetimeClosed:0}
stats After: sql.DBStats{MaxOpenConnections:1, OpenConnections:1, InUse:1, Idle:0, WaitCount:1, WaitDuration:343610117000, MaxIdleClosed:0, MaxIdleTimeClosed:0, MaxLifetimeClosed:0}
E0116 13:18:08.300386   47764 transaction.go:29] failed to rollback transaction: sql: transaction has already been committed or rolled back
W0116 13:18:08.300916   47764 engine.go:182] [/emulator/firebase 3004] ExecuteMutation TransactionTest: failed. Connector: core
Auth: public
Variables Set:
[id message updateMessage]
Errors: [message:"Database is not available\nTest record already exists! (aborted)" path:{values:{string_value:"query"}} extensions:{debug_details:"cannot reach the database: context canceled\n@check(expr) rejected the request: denied due to error: input: \n (aborted)\nCheck Requirement Evaluated: Every(path: query, DenyUnlessTrue(CEL(\"response.query.existingTest == null\" -> Boolean)))"} message:"(aborted)" path:{values:{string_value:"insert"}} message:"(aborted)" path:{values:{string_value:"update"}}]
Data Fields:
[insert update]
sources: core\users\mutations.gql [5025B] core\posts\mutations.gql [2962B] core\interactions\mutations.gql [1283B] core\interactions\queries.gql [1435B] core\comments\fragments.gql [527B] core\users\fragments.gql [228B] core\users\queries.gql [1651B] core\posts\fragments.gql [473B] core\posts\queries.gql [2192B] core\interactions\fragments.gql [201B] core\comments\mutations.gql [2999B] core\comments\queries.gql [1441B] core\test\mutations.gql [865B]
 {"metadata":{"emulator":{"name":"dataconnect"},"message":"E0116 13:18:08.299339   47764 execute.go:47] Database ping failed: input: \n after 5m43.610117s\nstats before: sql.DBStats{MaxOpenConnections:1, OpenConnections:1, InUse:1, Idle:0, WaitCount:0, WaitDuration:0, MaxIdleClosed:0, MaxIdleTimeClosed:0, MaxLifetimeClosed:0}\nstats After: sql.DBStats{MaxOpenConnections:1, OpenConnections:1, InUse:1, Idle:0, WaitCount:1, WaitDuration:343610117000, MaxIdleClosed:0, MaxIdleTimeClosed:0, MaxLifetimeClosed:0}\nE0116 13:18:08.300386   47764 transaction.go:29] failed to rollback transaction: sql: transaction has already been committed or rolled back\nW0116 13:18:08.300916   47764 engine.go:182] [/emulator/firebase 3004] ExecuteMutation TransactionTest: failed. Connector: core\nAuth: public\nVariables Set:\n[id message updateMessage]\nErrors: [message:\"Database is not available\\nTest record already exists! (aborted)\" path:{values:{string_value:\"query\"}} extensions:{debug_details:\"cannot reach the database: context canceled\\n@check(expr) rejected the request: denied due to error: input: \\n (aborted)\\nCheck Requirement Evaluated: Every(path: query, DenyUnlessTrue(CEL(\\\"response.query.existingTest == null\\\" -> Boolean)))\"} message:\"(aborted)\" path:{values:{string_value:\"insert\"}} message:\"(aborted)\" path:{values:{string_value:\"update\"}}]\nData Fields:\n[insert update]\nsources: core\\users\\mutations.gql [5025B] core\\posts\\mutations.gql [2962B] core\\interactions\\mutations.gql [1283B] core\\interactions\\queries.gql [1435B] core\\comments\\fragments.gql [527B] core\\users\\fragments.gql [228B] core\\users\\queries.gql [1651B] core\\posts\\fragments.gql [473B] core\\posts\\queries.gql [2192B] core\\interactions\\fragments.gql [201B] core\\comments\\mutations.gql [2999B] core\\comments\\queries.gql [1441B] core\\test\\mutations.gql [865B] \n"}}
Error: Unexpected initial message
    at _class5.handleClientMessage (C:\Users\user\AppData\Roaming\npm\node_modules\firebase-tools\node_modules\pg-gateway\dist\chunk-FCOSUQFU.cjs:1:212007)
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
    at async _class5.processData (C:\Users\user\AppData\Roaming\npm\node_modules\firebase-tools\node_modules\pg-gateway\dist\chunk-FCOSUQFU.cjs:1:211063)
    at async _class5.init (C:\Users\user\AppData\Roaming\npm\node_modules\firebase-tools\node_modules\pg-gateway\dist\chunk-FCOSUQFU.cjs:1:209869)
!!  dataconnect: Postgres threw an unexpected error, shutting down the Data Connect emulator: AbortError: The operation was aborted {"metadata":{"emulator":{"name":"dataconnect"},"message":"Postgres threw an unexpected error, shutting down the Data Connect emulator: AbortError: The operation was aborted"}}
i  emulators: Shutting down emulators. {"metadata":{"emulator":{"name":"hub"},"message":"Shutting down emulators."}}
i  ui: Stopping Emulator UI {"metadata":{"emulator":{"name":"ui"},"message":"Stopping Emulator UI"}}
i  extensions: Stopping Extensions Emulator {"metadata":{"emulator":{"name":"extensions"},"message":"Stopping Extensions Emulator"}}
[2026-01-16T19:18:08.307Z] [Extensions] Stopping Extensions emulator, this is a noop.
i  functions: Stopping Functions Emulator {"metadata":{"emulator":{"name":"functions"},"message":"Stopping Functions Emulator"}}
i  firestore: Stopping Firestore Emulator {"metadata":{"emulator":{"name":"firestore"},"message":"Stopping Firestore Emulator"}}
!  Firestore Emulator has exited upon receiving signal: SIGINT
i  pubsub: Stopping Pub/Sub Emulator {"metadata":{"emulator":{"name":"pubsub"},"message":"Stopping Pub/Sub Emulator"}}
!  Pub/Sub Emulator has exited upon receiving signal: SIGINT
i  auth: Stopping Authentication Emulator {"metadata":{"emulator":{"name":"auth"},"message":"Stopping Authentication Emulator"}}
i  storage: Stopping Storage Emulator {"metadata":{"emulator":{"name":"storage"},"message":"Stopping Storage Emulator"}}
[2026-01-16T19:18:08.330Z] Stopping rules runtime. {"metadata":{"emulator":{"name":"storage"},"message":"Stopping rules runtime."}}
i  eventarc: Stopping Eventarc Emulator {"metadata":{"emulator":{"name":"eventarc"},"message":"Stopping Eventarc Emulator"}}
i  dataconnect: Stopping Data Connect Emulator {"metadata":{"emulator":{"name":"dataconnect"},"message":"Stopping Data Connect Emulator"}}
# 108:fake shutdown
# skipped shmem_exit_index=5/6
# before_shmem_exit_index=4/6
2026-01-16 19:18:08.346 GMT [0] LOG:  shutting down
2026-01-16 19:18:08.347 GMT [0] DEBUG:  performing replication slot checkpoint
# skipped shmem_exit_index=3/6
# skipped shmem_exit_index=2/6
# skipped shmem_exit_index=1/6
# skipped shmem_exit_index=0/6
# dsm_backend_shutdown ?
!  Data Connect Emulator has exited upon receiving signal: SIGINT
i  tasks: Stopping Cloud Tasks Emulator {"metadata":{"emulator":{"name":"tasks"},"message":"Stopping Cloud Tasks Emulator"}}
i  hub: Stopping emulator hub {"metadata":{"emulator":{"name":"hub"},"message":"Stopping emulator hub"}}
i  logging: Stopping Logging Emulator {"metadata":{"emulator":{"name":"logging"},"message":"Stopping Logging Emulator"}}

@l1qu1d

Thanks for the detailed report @l1qu1d, I appreciate this! I was able to reproduce the issue, and as you mentioned, it is not reproducible on versions before 15.3.0. I'll raise this to our engineering team and will mark this as reproducible.

sharing the mcve here - https://github.com/aalej/issues-9756

@aalej

Thanks @aalej. I'm surprised this wasn't caught via testing. All database mutation types should have to go through tests before release for the Data Connect Emulator. I would like you to also suggest to the team that they please do so.

@aalej

Thank you for @aalej !

This is a pretty bad regression. I will looking into it shortly.

Yeah, our e2e test coverages in emulator + pglite is pretty limited right now.
We have good unit tests for core engine + Postgres, but quite limited for core engine + pglite.

Yeah, our e2e test coverages in emulator + pglite is pretty limited right now. We have good unit tests for core engine + Postgres, but quite limited for core engine + pglite.

I'm not sure what your limits are on the emulator + pglite but I believe it need to be a priority for your team. Many users and paying clients use the emulator (development & testing) before even touching production.

@l1qu1d

I fully agree that it is very important~
Emulator is an absolute critical part of Firebase Data Connect product. We are committed to keep it stable and up to date~

@l1qu1d Thank you for the kind feedbacks and raising this bug!
Sorry about the inconvenience caused

Root caused the underlying issue.

It turns out to be a one-line fix. A CLI release will be cut later today.

Thanks again for raising this bug quickly to our team!!

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Data Connect Emulator v3.0.2 Transaction Mutation Hang #9756

[REQUIRED] Environment info

[REQUIRED] Test case

[REQUIRED] Steps to reproduce

[REQUIRED] Expected behavior

[REQUIRED] Actual behavior

I suspect this excerpt from the full log result below:

Log after running the transaction.

Same log session, but after I reloaded the app because of the hang ~5 minutes later; emulator crashes

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Data Connect Emulator v3.0.2 Transaction Mutation Hang #9756

Description

[REQUIRED] Environment info

[REQUIRED] Test case

[REQUIRED] Steps to reproduce

[REQUIRED] Expected behavior

[REQUIRED] Actual behavior

I suspect this excerpt from the full log result below:

Log after running the transaction.

Same log session, but after I reloaded the app because of the hang ~5 minutes later; emulator crashes

Activity

aalej commented on Jan 19, 2026

l1qu1d commented on Jan 19, 2026

fredzqm commented on Jan 20, 2026

l1qu1d commented on Jan 20, 2026

fredzqm commented on Jan 21, 2026

fredzqm commented on Jan 21, 2026

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