3 ms·

> So a query that accesses 10 rows in disparate parts of the primary key space will take longer than one where the keys reside on the same splits. This is expec

by ex3ndr 10y ago

> So a query that accesses 10 rows in disparate parts of the primary key space will take longer than one where the keys reside on the same splits. This is expected with a distributed system. No, why? Query can be executed in parallel. BTW, isn't 20k/sec is a very very small performance for 30 node installation. Cassandra can handle 50k+ (both writes and read) on a single node. When in most queries you are trying to collect data from many nodes it will scale almost linearly.

daenney 10y ago
I don't think that comparison holds. It's easy to push 50k+ on a single node, you're basically only resource bound on that machine. Pushing 20k+ on something that's globally consistent spread out over so many instances is a different exercise entirely. It also depends on the level of consistency you're asking from Cassandra. You'd probably need to set this to EACH_QUORUM or ALL to mimic the behaviour Spanner gives you. And yes Cassandra will scale linearly-ish as long as you're in the same datacenter. Try running a geo-distributed 30-node Cassandra ring and it's a whole different story at that level of consistency and availability.
- ex3ndr 10y ago
  Sure, but you can make geo-replication and even implement proxy for providing consistency across DC, sure it won't be that fast in terms of latency, but throughput will be the same.
  - daenney 10y ago
    How does this proxy that provides cross-DC consistency work? And how does it guarantee that you'll get globally consistent reads? Most cases I've seen latency can affect throughput plenty so I doubt your assertion that it won't affect throughput quite a bit. Even more so for anything that relies on TCP/IP. I'd highly recommend reading the Bigtable[0] and Spanner[1] papers first and maybe then we can have a sensible and fruitful argument. [0]: https://research.google.com/archive/bigtable.html https://research.google.com/archive/bigtable.html [1]: https://research.google.com/archive/spanner.html https://research.google.com/archive/spanner.html

by ex3ndr 10y ago

daenney 10y ago

I don't think that comparison holds. It's easy to push 50k+ on a single node, you're basically only resource bound on that machine. Pushing 20k+ on something that's globally consistent spread out over so many instances is a different exercise entirely. It also depends on the level of consistency you're asking from Cassandra. You'd probably need to set this to EACH_QUORUM or ALL to mimic the behaviour Spanner gives you. And yes Cassandra will scale linearly-ish as long as you're in the same datacenter. Try running a geo-distributed 30-node Cassandra ring and it's a whole different story at that level of consistency and availability.

ex3ndr 10y ago
Sure, but you can make geo-replication and even implement proxy for providing consistency across DC, sure it won't be that fast in terms of latency, but throughput will be the same.
- daenney 10y ago
  How does this proxy that provides cross-DC consistency work? And how does it guarantee that you'll get globally consistent reads? Most cases I've seen latency can affect throughput plenty so I doubt your assertion that it won't affect throughput quite a bit. Even more so for anything that relies on TCP/IP. I'd highly recommend reading the Bigtable[0] and Spanner[1] papers first and maybe then we can have a sensible and fruitful argument. [0]: https://research.google.com/archive/bigtable.html https://research.google.com/archive/bigtable.html [1]: https://research.google.com/archive/spanner.html https://research.google.com/archive/spanner.html