Comment by bradleyjg | Hacker News Reader

Comment by bradleyjg | Hacker News Reader

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It is, but the details of the SLA aren't that great.

https://cloud.google.com/spanner/sla

"'Downtime' means, with respect to any Production-Grade Cloud Spanner Instance, more than a five percent Error Rate for the instance. Downtime is measured based on server side Error Rate. 'Downtime Period' means a period of five consecutive minutes of Downtime with a minimum of 60 requests per minute. Intermittent Downtime for a period of less than five minutes will not be counted towards any Downtime Periods."

For monthly downtown between 99.0% and 99.999% the customer is credited with 10% of the monthly bill. The customer is required to track the uptime and request an SLA credit.

> Intermittent Downtime for a period of less than five minutes will not be counted towards any Downtime Periods.

That's unfortunate. The most frustrating part about cloud services are exactly these kinds intermittent performance and responsiveness issues.

It probably won't count network downtime either, since it's measured at the server, not the client. Even if your client is in GAE...

That's like saying 'the most frustrating part about cloud services is that they use the internet.'

You're right, but that's basically 'by-design' as far as the internet is concerned.

Part of the problem is that computing the downtime at a higher resolution, in a way that scales from low-traffic users (the quoted minimum of 60 requests per minute is also not a coincidence) to very large ones, is not trivial.

You have to consider the rate at which the raw data is collected from the replicas ---and the jitter across all of them!-- then the rate at which that data is aggregated, and so on. (The above assumes that Cloud Spanner uses Borgmon for monitoring.) Any hiccups in the collection itself will result in less noise if you look at 5m vs e.g. 1m. You could increase the sampling rate, but then you're making your DB replicas spend more precious cycles on work that is not serving queries or replicating data.

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