Learn About

Timestamps in Riak TS are a critical data type, nearly always a part of partition key. They are often leveraged with the quantum function to group data by 15 minute clumps, or 10 second clumps, or 60 day clumps, et cetera, depending on how quickly your time series data come in and how you need to analyze them.

Structure of Timestamps

Unix Epoch Time

Timestamps in Riak TS are stored as positive integers representing the number of UTC milliseconds since January 1st, 1970 (UNIX epoch time).

As an example: midnight GMT, August 1st 2016, would exist in the database as the integer 1470009600000.

You can read more about UNIX epoch time here.

ISO 8601

For INSERT and SELECT statements, Riak TS supports ISO 8601 strings which are converted to UTC milliseconds.

A Note on ISO 8601 Support

ISO 8601 support is useful for casual interactions via riak shell, but we do NOT recommend using ISO 8601 in production applications. Instead, use the TS-supported client libraries to pass timestamps as integers for better performance and correctness.

Reduced Accuracy

Strings that do not include seconds are referred to as reduced accuracy representations.

Ambiguity can arise with reduced accuracy representations. For instance, what do the comparisons time > '2015' or time <= '2003-05-01T05:10' mean when translated to epoch time value as stored in Riak TS?

To resolve those ambiguities, Riak TS expands the reduced accuracy value to the lowest date/time which matches the specification. 2015 becomes 2015-01-01 00:00:00. 2003-05-01T05:10 becomes 2003-05-01T05:10:00.

For inserting data, that’s the full story. The expanded date/time value will be converted to epoch milliseconds and stored in the database.

For querying data, there are two important exceptions to the simple expand and convert sequence above.

1. Strictly greater than (>) and greater-than/equal-to (>=) queries involve incrementing the original reduced accuracy representation before expansion.

So, time > '2015' becomes in effect, time >= '2016-01-01 00:00:00', and

time <= '2003-05-01T05:10' becomes time < '2003-05-01T05:11:00'.

Thus, querying for timestamp values greater than '1970-12-18 21:00' will ignore any values which fall between 9pm and 9:01pm, while using a fully-specified string '1970-12-18 21:00:00' will include them.

2. Fractional times are not considered reduced accuracy, so selecting for timestamps greater than 2016-08-03 15:00 will give different results than 2016-08-01 15.0 (or 2016-08-01 15:00:00).

Time Zone FAQs

Why can’t Riak TS default to the operating system’s time zone instead of GMT if riak-admin is not used to set a time zone?

It is critically important that all servers in the cluster agree on the time zone to be used for translating time strings into timestamps. Defaulting to the operating system’s time zone is only safe if all servers in the cluster are guaranteed to be configured identically.

Why can’t I specify my time zone symbolically so I don’t have to change my default time zone when DST begins and ends?

Effectively for the same reason as question 1. Politicians love to mess with DST and time zones, and if one server in the cluster fails to get the latest time zone file updates, timestamps may be inconsistent depending on which server handles the translation from text to timestamp.

Can I set a different time zone for different tables?

Not yet.

Why does riak-shell display the results from select in GMT?

Riak TS does not yet expose the default time zone to clients.

Unsupported Formats

ISO 8601 includes three notable syntaxes which are not yet supported in Riak TS:

  • expanded representation (years outside the range 0000-9999),
  • time intervals (a range of times), and
  • week dates (a week or day expressed as a number of weeks into the year).