On Mon, Jul 11, 2016 at 11:56 AM, Emiliano Heyns <
[email protected]> wrote:

> On Monday, July 11, 2016 at 7:35:58 PM UTC+2, Sean Beckett wrote:
>>
>> Yes, you'd have a series for each unique trip ID. The car would be
>> identified by the "id" tag, presumably.
>>
>> You probably want to use a tag for "trip" so that you can group by trip
>> ID and performantly query by trip ID.
>>
>> However, if you anticipate millions of trip IDs, it would be better to
>> store it as a field so that your series cardinality
>> <https://docs.influxdata.com/influxdb/v0.13/concepts/glossary/#series-cardinality>
>> doesn't rise too high and require lots of RAM
>> <https://docs.influxdata.com/influxdb/v0.13/guides/hardware_sizing/#when-do-i-need-more-ram>
>> .
>>
>>
> Well, not millions. The first year we had an average of 350 trips over 3
> cars, so that should be OK. Over the next few years, we anticipate about 20
> car ids, and some 50k trips each (with two cars having the same trip ID
> would be very unlikely, although not impossible), so if I read that latter
> page right, we should be OK until the end of the project as long as we keep
> adding RAM. What's the Y axis on that latter chart?
>

The Y-axis is intentionally unit-less because the variance due to schema is
very significant. Same number of series with different schema can be 2-3x
different in terms of RAM used.

With 20 cars, 50k trips each over the next year that's one million series.
We will have caching of the in-RAM index available within the year, so
after that the series cardinality will no longer require massive RAM.

I think you're fine util the end of the project even if we don't allow
caching of the index. 5 million series lives pretty well in ~128GB, which
is not prohibitive today, and we've got a few more Moore's law cycles to
drive down cost.


> Is there a way to bulk-add tags to a set of existing measurements? We also
> want to add refuel points to our time series, but those can only be
> calculated later.
>

There is no way to add tags to points later. The series is determined by
the tag set, and is recorded at write time and cannot be changed without
making a new point. You can add new fields to points after the fact. Simply
write a new point with matching measurement name, tag set, and timestamp,
and the field set will be combined with the existing field set.


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-- 
Sean Beckett
Director of Support and Professional Services
InfluxDB

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