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Amazon Time Sync Service

aws.amazon.com

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Re: Amazon Time Sync Service

#61

Post by NavinF »

deelowe wrote: post #58
NavinF wrote: post #52

Earlier quoted context omitted.

You don’t even need a tcxo. If you don’t care about holdover, connecting the pps pin from a $5 GPS module to an $15 SBC will give you a time source that is significantly better than anything you can serve over NTP to your clients. NTP is always gonna be the weak link for a service like this.

I was referring to the amazon time sync service which I imagine has pretty tight timing requirements (similar to spanner), not NTP. Also, how exactly would GPS work at scale for 10,000s of servers within 1000s of racks within a DC?

As I understand it, “amazon time sync service” is just a bunch of NTP servers run by Amazon. Their ClockBound library calculates error bounds the same way you would if you were using a different NTP server: |Local Offset| + Root Dispersion + (Root Delay / 2)

>how exactly would GPS work at scale for 10,000s of servers

GPS module (+ GPSDO + Rb clock optional) -> SBC running NTP server -> machines running NTP client

I’m not sure what you meant by “clocks on the system board” but if you’re talking about the system clock on the NTP server or the NTP client, it really doesn’t matter. Any old crystal on the NTP server is accurate enough to stay locked to a PPS input. The clients are limited by NTP so their clocks don’t really matter either.

Re: Amazon Time Sync Service

#62

Post by pugworthy »

vel0city wrote: post #46
strimp099 wrote: post #34

Can someone please explain to me what this is all about like I’m five years old?

A person with two watches never knows what time it is.

Nah. They just figure out eventually one of them is kind of wonky and ignore it. Or maybe both are, so they end up just looking at the stove clock.

Also you can't tell a story just with the Aesop ending - you have to tell the fable and END with that line.

Re: Amazon Time Sync Service

#63

Post by baq »

bogomipz wrote: post #48
Groxx wrote: post #37

Earlier quoted context omitted.

Time is hard. By asking both super-microscopic stuff and stuff way out in space, you can now find out what time it is!

One is cesium? Whats the other stuff, way out in space?

Galileo sats use these

https://www.esa.int/Applications/Navigation/Galileo/Galileo_...

so, basically magic.

Re: Amazon Time Sync Service

#64

Post by staticassertion »

travisgriggs wrote: post #53
loxias wrote: post #43

Earlier quoted context omitted.

To be clear, what I meant was "the fact that they're advertising whiz bang time synchronization, but then not using the correct protocol, makes me question the quality of the whole enterprise". Even on local networks, NTP can only get you so close. If you set up chrony just so, in ideal conditions, I've gotten hundreds of microseconds (more commonly ~500-1000us). But combined with PTP, you can get sub-microsecond acc…

When Microsoft did that kind of thing we called it “embrace and extend.”

That sounds different. Embrace and extend means implementing a protocol and then adding specific non-spec features. For example, postgres 'embraces' SQL and 'extends' it with specific features - in the future postgres could 'extinguish' SQL by breaking from the spec, forcing an ecosystem split.

Re: Amazon Time Sync Service

#65

Post by pferde »

travisgriggs wrote: post #53
loxias wrote: post #43

Earlier quoted context omitted.

To be clear, what I meant was "the fact that they're advertising whiz bang time synchronization, but then not using the correct protocol, makes me question the quality of the whole enterprise". Even on local networks, NTP can only get you so close. If you set up chrony just so, in ideal conditions, I've gotten hundreds of microseconds (more commonly ~500-1000us). But combined with PTP, you can get sub-microsecond acc…

When Microsoft did that kind of thing we called it “embrace and extend.”

Microsoft already does offer PTP on Azure, and nobody calls it EEE.

https://docs.microsoft.com/en-us/azure/virtual-machines/linu...

Re: Amazon Time Sync Service

#66

Post by foota »

strimp099 wrote: post #34

Can someone please explain to me what this is all about like I’m five years old?

The combination of a time and guaranteed error bound can be used as a primitive in distributed systems. You can get timestamps from requests coming from different systems and relate them in a meaningful way. At least, in a false negative fashion. E.g., if A occurs at T + 100ms with 1ms uncertainty and B occurs at T + 105ms with 2ms uncertainty you can conclude that A happened before B. This does not allow you to always establish an order (e.g., if there is overlap) but this isn't always necessary. For instance if instead you are B and you want to have something occur after some time A with uncertainty A_uncertainty, then you can sleep until B with uncertainty B_uncertainty such that B - B_uncertainty > A + A_uncertainty.

Re: Amazon Time Sync Service

#67

Post by ithkuil »

LaserToy wrote: post #30
teraflop wrote: post #24

Earlier quoted context omitted.

Yes it did. Google published a paper about it in 2012, and claimed that at that point it had been in development for 5 years and in production for more than 1.

Mmm, I worked at google in 2012 and F1 was in active development. I’ve never heard of Spanner internally. Maybe it was in development, but it was not in use. Edit: went and read more. Looks like Spanner existed but didn’t have sql, so it wasn’t what it is today. And looks like I don’t remember things any more.

at least by 2013 it had some basic SQL (although much more limited subset that one usable today); if you needed more you would be using f1; IIRC I used spanner (without F1) in production around 2013

Re: Amazon Time Sync Service

#69

Post by oblio »

pugworthy wrote: post #62
vel0city wrote: post #46

Earlier quoted context omitted.

A person with two watches never knows what time it is.

Nah. They just figure out eventually one of them is kind of wonky and ignore it. Or maybe both are, so they end up just looking at the stove clock. Also you can't tell a story just with the Aesop ending - you have to tell the fable and END with that line.

I can't find the fable.

Re: Amazon Time Sync Service

#70

Post by oblio »

dekhn wrote: post #27
skj wrote: post #11

Earlier quoted context omitted.

Google uses map reduce extensively... where it's appropriate. True time helps with things like spanner transactions. It's just a totally different use case.

The tech lead of the Google MapReduce team (which no longer exists) just received their award for turning down mapreduce. IIRC it was officially done 5 years ago. However I believe the code to delete MR was never checked in and I'm not sure if there are still users. MapReduce was used at Google for highly inappropriate things. For example, the machine learning system I worked on, Sibyl https://www.datanami.com/2014/0…

> handle the constant failures endemic to Google's internal systems

This sounds bad.

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