This just sounds like a race condition gone weird. I assume from this description that the update protocol looks something like this: process-request:

This just sounds like a race condition gone weird. I assume from this description that the update protocol looks something like this: process-request: Update-local push to sync buddy wait for sync buddy success reply-with-status mark state as synced If the function does the local update and then gets stuck in the state waiting for the buddy to reply, one could imagine the failover daemon not handling that case very well. So while the master might not have acknowledged the transaction, the pair might get jammed trying to complete it. EBS is a particularily complicated piece of software, and RDS is another layer of complication built on top of that. Bugs clearly happen, and it's an unfortunate state of affairs.