Re: [Tzdist] Fwd: [tzdist] #32 (service): managing historical data

[Doug Royer <[e-mail]>]

On 12/14/2014 01:12 PM, Paul Eggert wrote:
> Cyrus Daboo wrote:
>> In that kind of environment, yes, every byte does count, because the 
>> sum of all
>> those extra bytes across the full set of users/devices is huge.
>
> In that case I'm puzzled why VTIMEZONE was chosen as the format for 
> data, as it's pretty fat.  For America/Los_Angeles, vzic generates a 
> VTIMEZONE format containing 4004 bytes, compared to the 1058 bytes 
> that Android uses for tz binary format.  If the problem is that 
> VTIMEZONE is bloated, perhaps a better solution would be to recommend 
> a more-compact data format.
>
> That being said, I'm still puzzled as to why shrinking the byte count 
> is so important that we should complicate the protocol to support it.  
> As a back-of-the-envelope calculation, suppose a VTIMEZONE zone is 
> 4000 bytes and we make the same assumptions as before for everything 
> else (32-bit native tz binary data is 1100 bytes, the tzdist request 
> is 200 bytes, the protocol overhead is 600 bytes for both request and 
> response, and there are 10 updates per year). Then we see the 
> following per-client costs over time:
>
> 0.0137 b/s VTIMEZONE full copy each request
> 0.0063 b/s 32-bit tz binary full copy each request
> 0.0035 b/s tzdist version-style no-change handshake
> 0.0030 b/s? ETag-style no-change handshake? (not clear what's involved 
> here)
>
> To give us some perspective on this, if we assume a single 
> reasonably-cheap server can process 300 Mb/s sustained, then a single 
> tzdist server could support 21 billion tzdist clients each using the 
> least-efficient protocol mentioned above.  That's pretty scalable: one 
> cheapish server should be able to handle the entire planet and then 
> some.  So why are we worrying so much about making every byte count?  
> Shouldn't it be more important to keep things simple?

The update might change 10 times a year. I would think the CUAs will be 
checking a lot more often just to see if today is one of the days an 
important TZ changed.

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Doug Royer - (http://K7DMR.us / http://DougRoyer.US)
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