On: Our Journey to PostgreSQL 12

[shoo]

> We then made the following changes to the subscriber database in order to speed up the synchronization: [...] Set fsync to off

I'm curious how much risk of data loss this added.

I guess the baseline is "we need to migrate before we run out of disk" I.e. you're either going to have data loss or a long period of unavailability if the migration cannot be carried out fast enough.

[ants_a → shoo]

If fsync is turned back on and a manual sync call is issued before considering the replica valid there will be no risk from this.

[tommyzli → shoo]

ants_a is correct. Also, our NVMe storage is ephemeral so you aren't recovering from a power loss anyways :)

[rubiquity → tommyzli]

Disclaimer: I work at AWS, not on EC2.

Locally attached disks are not ephemeral to instance reboots/power failures. However, the disks are wiped after instance terminations. On the official EC2 product pages this is called "instance storage" not "ephemeral storage."

[tommyzli → rubiquity]

TIL, this is really good to know! Do you know offhand if this is a new feature, or have I just always been wrong

[sk5t → tommyzli]

It's been that way for a long time - years at least. You can reboot but not 'stop' and of course not 'terminate.'