We just rushed out an urgent hotfix release for Synapse 0.26.1, addressing a nasty bug in the ujson library which causes it to misbehave badly in the presence of JSON containing very large >64-bit integers. Anyone whose synapses are currently filling up with "Value too big!" errors will want to upgrade immediately from https://github.com/matrix-org/synapse/releases/tag/v0.26.1.
Sorry for the inconvenience.
Changes in synapse v0.26.1 (2018-03-15)
- Fix bug where an invalid event caused server to stop functioning correctly, due to parsing and serializing bugs in ujson library.