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From Alexander Binzberger <alexander.binzber...@wingcon.com>
Subject Re: etcd performance comparison
Date Wed, 22 Feb 2017 09:05:10 GMT
1. Seams like it might make sense to increase snapCount for those tests.

2. ZK write performance also depends on the number of watches - afaik. 
This is not mentioned and not tested.

3. Does it really make sense to "blast" the store? Wouldn't it make more 
sense to compare fixed write/read per clients rates?

Am 22.02.2017 um 05:53 schrieb Michael Han:
> Kudus to etcd team for making this blog and thanks for sharing.
>>> I feel like they're running a questionable configuration.
> Looks like the test configuration
> <https://github.com/coreos/dbtester/blob/89eb8d31addff1d9538235c20878a8637f24608c/agent/agent_zookeeper.go#L29>
> does not have separate directory for transaction logs and snapshots as it
> does not have configuration for dataLogDir. So the configuration is not
> optimal. Would be interesting to see the numbers with updated configuration.
>>> They mention that ZK snapshots "stop the world", and maybe I'm mistaken, but
> I didn't think that was right
> Right, ZK snapshots does not block processing pipeline as it is fuzzy and
> it is done in a separate thread. The warning message "*To busy to snap,
> skipping*" mentioned in the blog is a sign that a snap shot is also
> generating in progress, which could be caused by the write contentions
> created from serializing transaction logs that leads to longer than
> expected snap shot generation. So "stop the world" is a side effect of
> resource contention, but not a design intention IMO.
> Also the blog mentions ZooKeeper as a key value store and I also want to
> point out that ZooKeeper is more than a (metadata) key value store has
> features such as sessions, ephemerals, and watchers, and these design
> choices were made I believe to make ZK more useful as a coordination
> kernel, and these design choice also (negatively) contribute to the
> performance and scalability of ZooKeeper.
> On Tue, Feb 21, 2017 at 4:32 PM, Dan Benediktson <
> dbenediktson@twitter.com.invalid> wrote:
>> I kind of wonder about them only using one disk. I haven't experimented
>> with this in ZooKeeper, nor have I ever been a DBA, but with traditional
>> database systems (which ZooKeeper should be basically identical to, in this
>> regard), it's a pretty common recommendation to put snapshots and TxLogs on
>> different drives, for the obvious reason of avoiding one of the biggest
>> problems laid out in that blog post: when snapshot happens, it contends
>> with your log flushes, causing write latencies to explode. Suddenly you
>> have tons more IO, and where it used to be nicely sequential, now it's
>> heavily randomized because of the two competing writers. It's kind of the
>> nature of benchmarks that there's always something you can nitpick, but
>> still, I feel like they're running a questionable configuration.
>> They mention that ZK snapshots "stop the world", and maybe I'm mistaken,
>> but I didn't think that was right - I thought they were just slowing
>> everything down because they write a lot and contend a lot. I'm pretty sure
>> ZK snapshots are fuzzy over a range of transactions, and transactions keep
>> applying during the snapshot, right?
>> Thanks,
>> Dan
>> On Tue, Feb 21, 2017 at 2:24 PM, Benjamin Mahler <bmahler@mesosphere.io>
>> wrote:
>>> I'm curious if folks here have seen the following write performance
>>> comparison that was done by CoreOS on etc, Consul, and ZooKeeper:
>>> https://coreos.com/blog/performance-of-etcd.html
>>> Sounds like performance comparison of reads and updates are coming next.
>>> Are there any thoughts from folks here on this comparison so far?
>>> Thanks,
>>> Ben

Alexander Binzberger
System Designer - WINGcon AG
Tel. +49 7543 966-119

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