6 ms·

You mean AP, not CA. CA doesn't exist.

raspasov 11y ago
Thanks man, good you caught it, I totally knew that, I need to be more careful with acronyms right after waking up :)
napoleond 11y ago
> CA doesn't exist. I'm not sure that's a good way of putting it. You can have databases that offer both consistency and availability, but they need to fit on a single machine (no partition tolerance).
- cjbprime 11y ago
  > I'm not sure that's a good way of putting it. You can have databases that offer both consistency and availability, but they need to fit on a single machine (no partition tolerance). Garbage collection requires (a delay that is indistinguishable from) partition tolerance. It's pretty illusory on single machines as well. Especially if they're multi-core.
  - Jweb_Guru 11y ago
    They might be related formally (though I'm not really sure). In practice, relational databases generally implement very special-purpose concurrent garbage collectors that will totally lock up only under pathological circumstances (though I won't pretend that it doesn't happen). If you're talking about GC in general, with special-purpose hardware and/or real time kernels, GC times can be bounded deterministically and are thus distinguishable from a partition (except in rare cases, as with all garbage collectors with cycle collection, where they must revert to stop-the-world because they can't reclaim memory fast enough). And, of course, it is possible to write actual real time systems that do not require garbage collection at all (though scant few of them have been formally verified to the extent that one might like).
- jhugg 11y ago
  CAP doesn't really apply to non-distributed systems. So I'm with the original sentiment. There is no CA.
politician 11y ago
It exists, it's just that assuming partitions never happen isn't very practical.
- Jweb_Guru 11y ago
  I may be incorrect, but my impression was that concurrent systems formalization (at least, in ways that are actually relevant on real hardware) was still an area of very active research. Is saying they exist meaningful even in a strictly theoretical sense?

Thanks man, good you caught it, I totally knew that, I need to be more careful with acronyms right after waking up :)

> CA doesn't exist. I'm not sure that's a good way of putting it. You can have databases that offer both consistency and availability, but they need to fit on a single machine (no partition tolerance).

cjbprime 11y ago
> I'm not sure that's a good way of putting it. You can have databases that offer both consistency and availability, but they need to fit on a single machine (no partition tolerance). Garbage collection requires (a delay that is indistinguishable from) partition tolerance. It's pretty illusory on single machines as well. Especially if they're multi-core.
- Jweb_Guru 11y ago
  They might be related formally (though I'm not really sure). In practice, relational databases generally implement very special-purpose concurrent garbage collectors that will totally lock up only under pathological circumstances (though I won't pretend that it doesn't happen). If you're talking about GC in general, with special-purpose hardware and/or real time kernels, GC times can be bounded deterministically and are thus distinguishable from a partition (except in rare cases, as with all garbage collectors with cycle collection, where they must revert to stop-the-world because they can't reclaim memory fast enough). And, of course, it is possible to write actual real time systems that do not require garbage collection at all (though scant few of them have been formally verified to the extent that one might like).
jhugg 11y ago
CAP doesn't really apply to non-distributed systems. So I'm with the original sentiment. There is no CA.

politician 11y ago

It exists, it's just that assuming partitions never happen isn't very practical.

Jweb_Guru 11y ago
I may be incorrect, but my impression was that concurrent systems formalization (at least, in ways that are actually relevant on real hardware) was still an area of very active research. Is saying they exist meaningful even in a strictly theoretical sense?