This version includes a [change](https://github.com/matrix-org/synapse/pull/12209)
to the way transaction IDs are managed for application services. If your
deployment uses a dedicated worker for application service traffic, **it must
be stopped** when the database is upgraded (which normally happens when the
main process is upgraded), to ensure the change is made safely without any risk
of reusing transaction IDs.
This version includes a [change](https://github.com/matrix-org/synapse/pull/12209) to the way transaction IDs are managed for application services. If your deployment uses a dedicated worker for application service traffic, **it must be stopped** when the database is upgraded (which normally happens when the main process is upgraded), to ensure the change is made safely without any risk of reusing transaction IDs.
See the [upgrade notes](https://github.com/matrix-org/synapse/blob/develop/docs/upgrade.md#upgrading-to-v1570) for more details.