Description

Large accounts or slow servers can mean that the client will retry /sync (without ?since) until it gets a result. However, the server's default cache time for sync responses seemingly went from some number of minutes to zero. This means that the server processes large /sync requests in the background but immediately throws away the result if the client gave up waiting and tried a second request.

There should be a non-zero default on the config value.

Steps to reproduce

• Be in thousands of rooms
• Have a slow-ish server
• Try to sync your account

Homeserver

t2l.io & t2bot.io

Synapse Version

1.60.0

Installation Method

pip (from PyPI)

Platform

N/A

Relevant log output

N/A

Anything else that would be useful to know?

No response