Mnesia with Memento lost all records for all tables

[Exadra37]

@vans163

The first thing that comes to mind is the node name changed, so the schema path changed. Like running
iex -S mix
then running
iex --sname test -S mix

That was not for sure the case. Nothing at all have changed, not even the code.

@vans163

The idea behind Mnesia is you MUST run it in at least 2 node configuration, as all writes go to both nodes, if 1 node has a power problem / CTRL+C+C, the other node will still receive the writes. (So 3 nodes total, your app + 2 noded mnesia). If you trip over the powercord to the rack hosting both nodes you are screwed and will lose (alot of) data.

If Mnesia cannot be use reliable with one single node it shouldn’t be allowed to even start or at least the docs could be very clear about that.

@vans163

There was ways around it, you can set the logdumpthreshold to 1 millisecond, so mnesia will dump the log every 1ms. Or set it to 1 write (default is 1000 i think). But dumping this log is very cpu intensive and your tables will lock up as the dump is done, large tables will be rendered unwritable.

Yes, I saw in my research that doing it so it will render it unusable

@vans163

If you want to run Mnesia in a single local node configuration (just to store some persistent state for your app in a simple way), id run it with logdumpthreshold 1 write.

I am still playing with some scripts in my laptop but for now it seems that we have an underline issue somewhere in the BEAM, because each time I use the scripts I have included in previous posts to write directly to the filesystem I loose data, because the BEAM seems to have a delay of around 2 seconds in my Laptop to actually write the data to the actual disk, even when I tell Ubuntu to not cache writes.

Another possibility is that my laptop SSD firmware is cheating when Ubuntu as write cache disabled and ignores it.