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Flux Usability Study and Language Proposal

Getting Started Querying with Flux and InfluxDB

NOTE BEFORE YOU GET STARTED: Forget much of what you know about Flux. This is a new version with some very important differences. As you work through this guide, please keep notes on your thoughts for each section as you encounter it. This ends in a test and you are expected to create a secret Gist with your thoughts and the answers to the questions. You can close with a summary of your feelings after going through the whole thing but please note your thoughts as you go along. It's very likely that you'll think something is crazy or off initially, but maybe think it's ok when you look back later to write your summary. We're interested in seeing this progression of your learning and thought process.

You're allowed to ask questions in the private channel set up for this usability test in Slack. #flux-usability-yourname

Welcome to the getting started guide for Flux. Flux is a functional scripting and query language that looks very similar to Javascript in some parts, but with shortcut syntax for common queries. Its goal is to make querying and working with data, and time series data in particular, easy and fast. While InfluxDB is the first class data source for Flux, it also provides adaptors to other databases, third party APIs, files, and formats that data can be represented in.

This guide doesn't present the entirety of the API or its functionality, but a subset to convey the essential concepts of the language. Go here for a complete Flux API reference.

Data Model

The data model of InfluxDB consists of Buckets, which hold data. Time series data is written in via the HTTP API and is represented as InfluxDB Line Protocol. It separates time series into measurements, tags, fields, and a time. Here are some examples of the InfluxDB line protocol:

cpu,host=serverA,region=west usage_system=23.2,usage_user=55.1 1566000000
events,app=foo description="something happened",state=1i 1566000000

In the first line you have a measurement named cpu, two tag key/value pairs of host=serverA and region=west, two fields of usage_system=23.2 and usage_user=55.1 and a timestamp at the end of 1566000000. Measurement names and tag values are always strings. Fields can be either float64, int64, bool, or string. The second line in the snippet has data for the events measurement and shows a string and integer field value.

The combination of a measurement, tags, and a specific field represent an individual time series, which are an ordered list of time, value pairs. For example, cpu,host=serverA,region=west usage_system would be one time series from line 1 in the above example. You can generally think of tags as the dimensions on which you can query and slice and dice your time series data. However, you can also do that with fields, provided that you pay attention to performance and schema design considerations.

With the data in InfluxDB it's important to keep this context of a time series in mind. There are different types of numbers that can be recorded in time series and many operations only make sense when performed on an individual series and then later combined in some other way. Here are some examples of data that is fed in a time series:

Metrics

Metrics are regular time series that are values captured at specific intervals of time (like every 10 seconds or 1 minute or 1 hour or 1 day). There are different kinds of metrics that are commonly captured

  • counter - A value that counts the occurrence of an event. Counters alway increase unless they have been wrapped or reset. A reset occurs when what ever is doing the counting is restarted in which case it starts counting again from 0. A wrapped counter is one that has reached the largest number allowed by the byte representation of the value, in which case it starts over again at 0. These wraps and resets need to be accounted for when performing operations on counters. An example of a counter is the number of bytes a network interface has received.
  • gauge - A value that measures a specific value, which can increase or decrease. An example of a gauge is taking a temperature reading.

Events

Events are single data points in time. This could be an individual request to an API and how long that took, a user logging into a service, a car parking, a light turning on, a container starting or stopping, or anything you can think of. Events are what are called irregular time series given that they can occur at any time. It is possible to create regular time series from an underlying event stream (like counting how many occurred every five minutes for the last hour).

Working with data in Flux

When working with data in Flux, it translates the line protocol/time series structure into to a table. You can think of a measurement name as a table with the tag and field keys representing columns. Flux also includes the reserved column, time, in every table pulled from InfluxDB. The time column is the time at the end of the line protocol when data is written in.

Here's an example of line protocol and its translation to a Flux table:

h2o_temperature,location=santa_monica,state=CA surface_degrees=65.2,bottom_degrees=50.4 1568756160
h2o_temperature,location=santa_monica,state=CA surface_degrees=63.6,bottom_degrees=49.2 1600756160
h2o_temperature,location=coyote_creek,state=CA surface_degrees=55.1,bottom_degrees=51.3 1568756160
h2o_temperature,location=coyote_creek,state=CA surface_degrees=50.2,bottom_degrees=50.9 1600756160
h2o_temperature,location=puget_sound,state=WA surface_degrees=55.8,bottom_degrees=40.2 1568756160
h2o_temperature,location=puget_sound,state=WA surface_degrees=54.7,bottom_degrees=40.1 1600756160
location state surface_degrees bottom_degrees time
coyote_creek CA 55.1 51.3 1568756160
coyote_creek CA 50.2 50.9 1600756160
puget_sound WA 55.8 40.2 1568756160
puget_sound WA 54.7 40.1 1600756160
santa_monica CA 65.2 50.4 1568756160
santa_monica CA 63.6 49.2 1600756160

Note that the measurement name doesn't appear anywhere. That's because the table itself represents data from the h2o_temperature measurement. Later we'll see how to work with multiple measurements (i.e. tables). Note that the underlying time series would be represented by the combination of location, state, and the specific field. Results are ordered by default by the columns of the tags and their values and then by time. So we can see that coyote_creek, CA rows are together in time ascending order.

We'll show later how to specify to the graphing engine what represents an individual time series that you want visualized.

Basic Queries

This section will explore some basic queries in Flux to highlight the syntax and a few of the basic concepts of the language. For these examples, we'll assume a dataset that has a schema like the one seen above.

Introduction to basics and getting the last value

In this example, we'll get the last value of surface_degrees for every series in the h2o_temperature measurement in the my_data bucket. Flux has a shorthand syntax for the common operation of selecting data from a bucket with given criteria for a given time range. Let's look at that first for this example:

@my_data.h2o_temperature{surface_degrees, time}

The @ symbol at the beginning indicates that we're using the shorthand syntax and that the next set of characters will identify the bucket name. After that we have a . separator, followed by the measurement name of h2o_temperature. Immediately following that we have the Column Filter Predicate syntax (the curly braces { and } and what's inside of them) to indicate which columns we want in the result. The identifiers can also be wrapped in double quotes, which you'll need to use if they contain spaces:

@"my_data"."h2o_temperature"{"surface_degrees", "time"}

Given the previous data set, this query would produce a result like this:

surface_degrees time
50.2 1600756160
54.7 1600756160
63.6 1600756160

Since we didn't specify a time range in the query, we get the most recent data point for each series. How far back in time the database looks for a recent value is dependent on the setup of the backend InfluxDB system you are working with (this will typically be less than a few hours). We'll show how to specify explicitly how far back to look for the most recent value in a moment.

In this result set we have three rows, but we can't see their series information (i.e. the tags) because we didn't select them. Selecting them is fairly easy:

@my_data.h2o_temperature{location, state, surface_degrees, time}

Would return the last value of surface_degrees in each series:

location state surface_degrees time
coyote_creek CA 50.2 1600756160
puget_sound WA 54.7 1600756160
santa_monica CA 63.6 1600756160

In Flux, a tag key and a field key are both called columns. This means that tag keys and field keys must be unique within a measurement. Here's an example that explicitly selects all the columns we know about:

@my_data.h2o_temperature{location, state, surface_degrees, bottom_degrees, time}

We can also select all columns by leaving the column list empty:

@my_data.h2o_temperature{}

Or you can leave out the curly braces:

@my_data.h2o_temperature

If your Column Filter Predicate selects only a tag, you'll get the same number of records as you have series for that tag since the last value for each series is what gets defined if you're not filtering by time range or other criteria.

@my_data.h2o_temperature{state}

Returns these results:

state
CA
CA
WA

Filtering on Criteria

You can limit the results returned in the query by specifying filtering criteria in the Column Filter Predicate block. Here's an example that filters based on the location:

@my_data.h2o_temperature{location, surface_degrees, time, state == "CA"}
location state surface_degrees time
coyote_creek CA 50.2 1600756160
santa_monica CA 63.6 1600756160

Note that state is returned in the result because it was listed in the filter criteria. You can have more complex logic to match criteria like:

@my_data.h2o_temperature{location, surface_degrees, time, location == "coyote_creek" OR location == "puget_sound"}

See that while the column names are separated by commas, the filter criteria is separated by the different matching clauses.

Matching Critera

There are many operators you can use to filter down data. Here is the list of operators:

  • == (equal to)
  • != (not equal)
  • =~ (regex match)
  • !~ (not a regex match)
  • > (greater than)
  • >= (greater than or equal to)
  • < (less than)
  • <= (less than or equal to)
  • in

The regex and in operators are probably the trickiest ones to work with, so here are a few examples:

// this is a comment because it has // before it

// status is a tag and this will match any stats between 200 and 500
@my_data.http_requests{status =~ /[2-5][0-9][0-9]/}

// will match states in the array
@my_data.h2o_temperature{state in ["CA", "WA"]}

Aggregate, Select, Transform and Group Data

Flux has many built in functions to work with time series data. Aggregate functions refer to functions that summarize some period of time. They take N rows and output a single result, examples include count, mean, and percentile, among many others. Select functions select a set of rows from an input set based on some criteria. Min, max, top, and bottom are examples of selectors. Some selectors also double as aggregates like min and max.

This is an important distinction. An aggregate produces new data from some source data. That new data is frequently a summary statistic that describes the source data in some meaningful way. A selector specifies criteria for selecting rows from some source data. So you're not transforming the data when using a selector. For example, count is not a function that could be used as a selector.

Sample Dataset

Here's an example dataset that we'll use for the rest of the examples in this section. The raw number timestamps have been replaced with human readable times and the values have been set to simple whole numbers to make things easier. The example times only go down to minute precision to make things easier, but you can summarize down to the nanosecond.

h2o_temperature,location=santa_monica,state=CA surface_degrees=65,bottom_degrees=50 2020-02-22T15:01
h2o_temperature,location=santa_monica,state=CA surface_degrees=64,bottom_degrees=49 2020-02-22T15:31
h2o_temperature,location=santa_monica,state=CA surface_degrees=63,bottom_degrees=49 2020-02-22T16:01
h2o_temperature,location=santa_monica,state=CA surface_degrees=62,bottom_degrees=49 2020-02-22T16:31
h2o_temperature,location=santa_monica,state=CA surface_degrees=61,bottom_degrees=48 2020-02-22T17:01
h2o_temperature,location=santa_monica,state=CA surface_degrees=60,bottom_degrees=48 2020-02-22T17:31
h2o_temperature,location=santa_monica,state=CA surface_degrees=60,bottom_degrees=48 2020-02-22T17:46
h2o_temperature,location=coyote_creek,state=CA surface_degrees=55,bottom_degrees=51 2020-02-22T16:05
h2o_temperature,location=coyote_creek,state=CA surface_degrees=53,bottom_degrees=50 2020-02-22T17:05
h2o_temperature,location=puget_sound,state=WA surface_degrees=55,bottom_degrees=40 2020-02-22T17:10
h2o_temperature,location=puget_sound,state=WA surface_degrees=54,bottom_degrees=40 2020-02-22T17:40

In the data set we can see there are three distinct keys and that the time range of data is from 2020-02-22T15:01 to 2020-02-22T17:46 (about a two and a half hour span). There are more data points for the santa_monica, CA location than for the others. The differing number of values will be instructive later when we shape and summarize this data.

Summarizing and Grouping with Aggregates

Let's get into an example for summarizing some of our water data. For the sake of these queries, assume that we're executing them at 2020-02-22T18:00, that way we can use relative times in the query. Say we want to get the last 3 hours of data, with the min, max, and mean of bottom_degrees for that time period. With that definition, we'd expect to get 1 row per series in the dataset (assuming that we have min, max, and mean as columns in the resulting table. Here's the query:

@my_data.h2o_temperature{bottom_degrees, time > -3h}
    |> aggregate({min(bottom_degrees), max(bottom_degrees), mean(bottom_degrees)}) 

Will return the following dataset:

min_bottom_degrees max_bottom_degrees mean_bottom_degrees
48 51 47.45

Even though the sample data set has three series, we get back only a single row that gives the summary statistics we requested. The call to the aggregate function passed in an Aggregate Summary Block which looks similar in construction to the Predicate Filter Block that we used on the first line of the query. The returned column names are given automatically based on the construction <function name>_<field name>. As with the other blocks, field names can be wrapped in double quotes to handle cases like spaces or other special characters in a field name.

Our results don't have the descriptive tag metadata because we didn't ask for it. Selecting location and state which are the two tags that we have for data in the h20_measurements measurement will ensure it comes through in the aggregate and we can then group by those columns:

@my_data.h2o_temperature{location, state, bottom_degrees, time > -3h}
    |> aggregate({min(bottom_degrees), max(bottom_degrees), mean(bottom_degrees)}, by: ["location", "state"]) 
location state min_bottom_degrees max_bottom_degrees mean_bottom_degrees
coyote_creek CA 48 50 48.714
puget_sound CA 40 40 40
santa_monica WA 50 51 50.5

Although we could have left out the state grouping from our example because in this case the location is enough to unique identify a series.

Say we wanted to get a summary per state:

@my_data.h2o_temperature{location, state, bottom_degrees, _time > -3h}
    |> aggregate({min(bottom_degrees), max(bottom_degrees), mean(bottom_degrees)}, by: ["state"]) 
state min_bottom_degrees max_bottom_degrees mean_bottom_degrees
CA 48 51 49.11
WA 40 40 40

See that the results don't have the location column even though we selected it on the first line. That's because it wasn't included in the by set of columns in the call to aggregate.

The aggregate function can window the data by time intervals. For example, if we wanted to summarize each hour for the last three hours:

@my_data.h2o_temperature{location, bottom_degrees, time > -3h}
    |> aggregate({min(bottom_degrees), max(bottom_degrees), mean(bottom_degrees)}, by: ["location"], window: 1h) 

Because the aggregate function is breaking the records out into one hour intervals, the time column is kept, but the values are updated to the end of the window. For example, data at 2020-02-22T16:05 would get summarized in a record with the time value (window) of 2020-02-22T17:00.

location min_bottom_degrees max_bottom_degrees mean_bottom_degrees time
santa_monica 48 50 48.714 2020-02-22T16:00
santa_monica 48 50 48.714 2020-02-22T17:00
santa_monica 48 50 48.714 2020-02-22T18:00
coyote_creek 51 51 50 2020-02-22T17:00
coyote_creek 50 50 50 2020-02-22T18:00
puget_sound 40 40 40 2020-02-22T18:00

Remember there were three series, so for 1h summaries for the last 3 hours we'd expect to have three rows per group for nine total rows. But looking at the results, we only see the full three summaries for the santa_monica location. This is because the other two series don't have data in every window of time.

You can create rows for the missing summaries by calling interpolate after the call to aggregate. It can be used to fill in default values or values based on a summary statistic of the rows like first, min, max, mean, etc. You can find the details for interpolate in the function reference.

Select

The select function works similar to aggregate in that it operates on windows of time and groupings of rows. However, The difference is that select returns specific rows, rather than a summary data point. Here are a few examples:

@my_data.h2o_temperature{location, state, bottom_degrees, surface_degrees, _time > -3h}
    |> select({min(bottom_degrees)}, by: [])
location state bottom_degrees surface_degrees time
puget_sound WA 40 55 2020-02-22T17:10
puget_sound WA 40 54 2020-02-22T17:40

Notice that all the columns are pulled through, the selected column name remains the same and note that we've pulled in two records. We pull in two records because both of those have the same min bottom_degrees value of 40, which is the min for all records in that time. Notice also that time is the same value as those individual records, which you don't see in calls to aggregate.

If you pass in multiple columns, they are used as secondary selectors (kind of like sorting by multiple columns) for example:

@my_data.h2o_temperature{location, state, bottom_degrees, surface_degrees, _time > -3h}
    |> select({min(bottom_degrees), max(surface_degrees)})

produces:

location state bottom_degrees surface_degrees time
puget_sound WA 40 55 2020-02-22T17:10

Or calling select with {min(bottom_degrees), min(surface_degrees)} produces:

location state bottom_degrees surface_degrees time
puget_sound WA 40 54 2020-02-22T17:40

You can also select in groups based on time or by other columns, just like you can with aggregate. Here's an example using time grouping and inserting the time window for associated row selections:

@my_data.h2o_temperature{location, state, bottom_degrees, _time > -3h}
    |> selector({max(bottom_degrees), by: ["state"], window: 1h, windowColumn: "window")

// if you include window_column, the result will put the window timestamp for each selected row in that column

Produces this result:

location state bottom_degrees time window
santa_monica CA 50 2020-02-22T15:01 2020-02-22T16:00
coyote_creek CA 51 2020-02-22T16:05 2020-02-22T17:00
santa_monica CA 48 2020-02-22T17:01 2020-02-22T18:00
santa_monica CA 48 2020-02-22T17:31 2020-02-22T18:00
santa_monica CA 48 2020-02-22T17:46 2020-02-22T18:00
puget_sound WA 40 2020-02-22T17:10 2020-02-22T18:00
puget_sound WA 40 2020-02-22T17:40 2020-02-22T18:00

What this does is for each 1 hour period, it groups the rows by state and then selects the rows with the max value. Because we included the windowColumn argument, that is included in the result with the ending timestamp of the window that each record fell into.

Since so many of the records have tied max(bottom_degrees) values, we see that many of the original rows were selected in the result. We can also see the window that is inserted to specify which block of time the selector was working across.

The following functions can be used in the Selector Predicate Block: first, last, min, max, top, bottom

Calling Aggregates and Selectors without Aggregate or Select

The aggregate and select functions provide a shorthand for computing based on multiple columns. However, the functions passed in can also be called on tables. For example:

// get the most recently written record
@my_data.h2o_temperature |> last()

// get the most recently written record for each location
@my_data.h2o_temperature |> last(by: ["location"])

// get the average for each hour for each location
@my_data.h2o_temperature{time > -3h} |> mean(by: ["location"], window: 1h)

Count, Distinct, and CountDistinct

The count function is an aggregate while the distinct function is a selector. The countDistinct function is a helper function that will combine operations for you.

@my_data.h2o_temperature{state, time > -3h}
    |> select({distinct(state)}, time: 1h, windowColumn: "time")

Would return the following result

state time
CA 2020-02-22T16:00
CA 2020-02-22T17:00
CA 2020-02-22T18:00
WA 2020-02-22T18:00

We can see that CA reported in all three hours while both CA and WA reported in only the last hour. Also see that distinct discards columns that aren't in the by argument or the distinct column itself. So we use the time name for where we put the window markers for each distinct state. You could then count the number of states reporting per hour:

@my_data.h2o_temperature{state, time > -3h}
    |> select({distinct(state)}, time: 1h)
    |> timeShift(-1m)
    |> aggregate({count(state)}, time: 1h)

Would produce:

state time
1 2020-02-22T16:00
1 2020-02-22T17:00
2 2020-02-22T18:00

See that we had to use the timeShift function to move the timestamps of the windows back so that the resulting times would be accurate for aggregate.

All of this is encapsulated by the countDistinct function. For example, if we wanted to count the number of distinct locations that reported in each sate for each hour in the last three hours.

@my_data.h2o_temperature{location, state, bottom_degrees, time > -3h}
    |> countDistinct(location, by: ["state"], window: 1h)

Math, basic transformations, and using previous results in new queries

Flux makes it easy to do basic math and transformations across tables of data. First, let's look at renaming columns. All of the different predicate blocks recognize the as keyword to rename. For example:

@my_data.h2o_temperature{location, state, bottom_degrees as degrees, top_degrees, time}

// or renaming columns in an aggregate:
@my_data.h2o_temperature{bottom_degrees, time > -1h}
    |> aggregate({min(bottom_degrees) as min, max(bottom_degrees) as max})

Here are some examples of doing math and introducing the concept of variables:

temps = @my_data.h2o_temperature{bottom_degrees, surface_degrees, time, location == "coyote_creek"}

// do some math and return a new table with an addition column. Note that as is required on the end. Resulting
// table will have all the columns of the previous on and this new one
new_table = temps.surface_degrees - temps.bottom_degrees as bottom_surface_difference

// or you can pipe forward it to another function
temps.surface_degrees - temps.bottom_degrees as bottom_surface_difference
    |> sort(by: ["bottom_surface_differrence"])

// convert from fahrenheit to celsius and replace the value previously held by bottom_degrees
(temps.bottom_degrees - 32) * 5 / 9 as bottom_degrees

The above example shows assigning a result set to a variable so that it can be used multiple times later. You can also use this construction to do implicit joins across tables. Here's a made up example:

foo_data = @my_data.foo{value as foo_val, and time > -1h}
bar_data = @my_data.bar{value as bar_val, and time > -1h}

foo_data.foo_val - bar_data.bar_val as difference_to_bar

The above call will do a join between the two tables and rows based on all string columns matching and the time. The result data set will include all columns from both tables along with the new column differece_to_bar. If a column of the same name exists in both tables, the value from the left hand side table will be used (foo_data in this example). So this result would have the columns:

foo_val bar_val difference_to_bar time

Advanced Concepts

We'll fill this in later. Topics will include joins, unions, map, and reduce. We shouldn't need any of these more explicit operations to answer the questions in this test. The implicit joins via math should be enough to make this work. However, there is one trick you'll likely need...

Using Data From a Previous Result in a new Query

You can query the database for results and use either a record, an individual value, or an entire column in subsequent queries. This is useful for pulling back data from top results, etc. Here's an example:

// get the top 10 locations in terms of surface degrees
top_temps = @my_data.h2o_temperature{surface_degrees, location}
    |> selector({top(surface_degrees, 10)})

// now get the last hour of data for those 10 locations
@my_data.h2o_temperature{location in top_temps.location and time > -1h}

Function Reference for Test

In addition to the getting started guide above, you'll need some combination of the following functions to complete the answers for the test. This is by no means a complete API reference, but only a limited set of functions required to complete this task. You may or may not use all of these functions, depending on how you choose to solve each problem.

Note that the function definitions all contain named arguments, which are also positional. The first argument is always table, since the first argument is always what receives the pipe forward. For example if we had this:

// define functon foo
foo = (table, columnName) => {
    // some function definition here
}

// we can call it like
some_table |> foo("my_column")

// or like this
some_table |> foo(columnName: "my_column")

// or like this
foo(some_table, "my_column")

// or like this
foo(some_column, columnName: "my_column")

// or like this
foo(table: some_column, columnName: "my_column")

Aggregate

Aggregate will take aggregate functions like quantile, min, max, mean, count and others. It groups data by the given columns and windows of time.

aggregate = (table, fn, by = [], window = 0) => {}

The default window argument of zero means that the aggregate will be computed for all time seen in the table. That is, a single row will be returned per group.

Select

Select will take selector functions like top, bottom, min, and max and select rows matching the given function by the given columns and time.

select = (table, fn, by = [], window = 0) => {}

Max

Max works as either an aggregate or a selector. If used in an aggregate it will return a single value that is the max for the given grouping and time window. If used in a selector, it will return the rows that have the max value for the grouping and window.

max = (table, column) => {}

Min

Min works as either an aggregate or a selector. If used in an aggregate it will return a single value that is the min for the given grouping and time window. If used in a selector, it will return the rows that have the min value for the grouping and window.

min = (table, column) => {}

Mean

Mean is an aggregate function (so it can only be used as an argument to aggregate).

mean = (table, column) => {}

Count

Count is an aggregate function (so it can only be used as an argument to aggregate).

count = (table, column) => {}

Top

The top function is passed into select to produce the top n rows per grouping per window of time.

// notice that top takes a view, which is what the selector function sends to it. Top can only be 
// used as an argument to selector. N is the number of results you'd like
top = (table, column_name, n) => {}

Sort

Sort will sort the results in the table.

sort = (table, by, desc = true) => {}

Rate

Rate will compute the rate on a units per interval based on the passed in parameters. It is called on its own and not as an argument to select or aggregate. It can be used to compute the rate for individual series, or for the sum across a number of series, all depending on what is passed to by.

// function signature
rate = (table, columns, period = 1s, by = [], window = 0) = {}

We can see that only the table and columns arguments are required with the other arguments being optional. Columns is a map with the key being the new column name and the value being the column you're computing a rate on. So you can compute the rate for multiple columns on a single call to the rate function.

Period determines what the rate period is (like per second, minute or hour). The by argument specifies what dimensions you'd like to compute a rate on. If this is passed in, but no window is passed the result will be a single row per grouping, which represents the average rate of that entire grouping over the whole time period.

If you wanted to get rate in time windows, you'd pass in window so for example, you could see the rate in per minute units for every hour for the last 24 hours (assuming you queried 24 hours of data to begin with).

The rate function wraps up all of the math operations required to calculate a rate across multiple dimensions so you won't have to worry about coming up with a nonsensical result.

// computing the rate on individual series. This will calculate the rate on a point to point basis from 
// column named value and put the result in units_per_second. value will not be in the result set as it
// no longer applies
data |> rate({value as units_per_second}, by: ["column1"])

// you can compute the rate on a per minute 
data |> rate({value as units_per_minute}, by: ["column1", "column2"], period: 1m)

// you can compute on some other dimension in per second units with one point per 10m
data |> rate({value as units_per_secod}, by: ["region"], window: 10m)

Rate wraps a number of calls into one thing depending on which arguments you pass in. With any call to rate, it starts with computing the rate between individual value,time pairs in each series. If you havn't passed in a time or by arugment, you're done. If you passed in a time arugment, rate will then call aggregate and compute the mean rate across those windows of time. If you passed in a by argument, it will then call aggregate again, but this time computing the sum of the previous means. This progression is very specific and often trips people up, so we've wrapped it in this function so you don't have to remember the correct order to get a useful result.

Increase

Increase works on columns that are counters. Like the rate function, it is called by itself (not as an argument to aggregate or selector). Its arguments by and window operate in the same way that rate does. It will calculate the total increase accounting for resets in the counter (note this increase is not like the old Flux one). For example, this could be used to determine the total number of bytes send over a network card in a given window of time.

increase = (table, columns, by = [], window = 0) = {}

Filter

Filter will filter a result set to the requested columns and records matching the predicate criteria.

// function signature
filter = (table, fn) => {}

// calling it
data |> filter({foo == "bar"}) // will return all columns in data, but only rows matching criteria

data |> filter({foo == "bar" and time > -3h and time < -1h}) // will return only rows in specified time range

data |> filter({foo, colA, foo == "bar"}) // will return only the foo, colA and system columns

data |> filter(fn: {foo == "bar"}) // example calling with explicit parameter named

Drop

Drop will drop the specified columns from the table, including system columns if requested:

// function signature
drop = (table, columns) => {}

// calling it
data |> drop(["foo", "_key"])

Keep

Keep will keep only the specified columns in the table, while keeping any system columns (starting with _):

// function signature
keep = (table, columns) => {}

// calling it
data |> keep(["foo", "_time"])

Rename

Rename will rename a column from one thing to another. Note that the _key values will not be altered even if that column appears in the key. Here's the function signature and how it can be called:

// function signature
rename = (table, from, to) => {}

// calling it
data |> rename(from: "foo", to: "bar")

Graphing

In order for the visualization front end to know which rows group into a series, you can call the graph function that will include in the result set information about what constitutes a series that should be graphed. This function must be called if you will be visualizing with any kind of graph with an x and y axis. Nothing need be done for tables and single stat panes. In the future, Flux will have functions instructing the front end to visualize and structure the data in any of the ways it supports, like single stat panes, tables, bar charts, line graphs, heatmaps, histograms and many more.

Here's an example of the basic graph call:

@my_data.cpu{host, usage_system, usage_user, time, cpu == "cpu-total" AND time > -1h}
    |> graph(yCols: ["usage_system", "usage_user"], xCol: "time", by: ["host"])

The Test

For the following questions, you will need to write the query that you think will give the desired result and write a small sample of what you expect the text result from the API to look like. Your answer should be a secret Gist as a single Markdown file. Your query should be wrapped in code blocks and your result expectation should be a markdown table (like used in this guide earlier).

These questions intentionally leave out metadata queries as those are likely to be single functions once we refine things. These questions are based on something like Telegraf data from cpu, mem, disk, and net. There’s also another measurement for http_requests_total from some service.

Example Data

The cpu measurement looks like this:

cpu,host=serverA,region=east usage_system=0.5,usage_user=0.6 1568756160
cpu,host=serverB,region=east usage_system=0.5,usage_user=0.6 1568756160
cpu,host=serverC,region=west usage_system=0.5,usage_user=0.6 1568756160
cpu,host=serverD,region=west usage_system=0.5,usage_user=0.6 1568756160

where the fields usage_system and usage_user are gauges.

The mem measurement looks like this:

mem,host=serverA,region=east used_percent=50 1568756160
mem,host=serverB,region=east used_percent=50 1568756160
mem,host=serverC,region=west used_percent=50 1568756160
mem,host=serverD,region=west used_percent=50 1568756160

where the field used_percent is a gauge between 0 and 100.

The disk measurement looks like this:

disk,host=serverA,region=east,path=/ used_precent=50 1568756160
disk,host=serverA,region=east,path=/mnt/media used_precent=50 1568756160
disk,host=serverC,region=west,path=/ used_precent=50 1568756160
disk,host=serverC,region=west,path=/mnt/media used_precent=50 1568756160

where the field used_percent is a gauge between 0 and 100.

The net measurement looks like this:

net,host=serverA,region=east,interface=eth0 bytes_in=1000,bytes_out=18548 1568756160
net,host=serverA,region=east,interface=eth1 bytes_in=1000,bytes_out=18548 1568756160
net,host=serverC,region=west,interface=eth0 bytes_in=1000,bytes_out=18548 1568756160
net,host=serverC,region=west,interface=eth1 bytes_in=1000,bytes_out=18548 1568756160

where the fields bytes_in and bytes_out are counters.

The http_request_total measurement looks like this:

http_request_total,host=serverA,region=east,service=log,status=200 value=8978 1568756160
http_request_total,host=serverA,region=east,service=auth,status=200 value=8978 1568756160
http_request_total,host=serverA,region=east,service=auth,status=503 value=8978 1568756160
http_request_total,host=serverC,region=east,service=log,status=200 value=8978 1568756160
http_request_total,host=serverC,region=east,service=auth,status=200 value=8978 1568756160
http_request_total,host=serverC,region=west,service=auth,status=503 value=8978 1568756160

where the field value is a counter.

Questions

For the following questions, answer each letter (e.g. 1.i, 1.ii, etc). Make each a ## heading in your Gist. Please also include your thoughts about the language and each question as you go through. These can be raw stream of consciousness thoughts, we want any random thoughts you have as you go through the test.

  1. Get the last value and host seen for the cpu measurement and the usage_system field

    1. You want the host, value, time (this is for a single stat pane, a single host)
    2. You want the last value, host, time for each host (this is for a tabular view)
    3. You want the last value, host, time for each host, but only in the uswest region (this is for a tabular view)
  2. Get usage_system and usage_user from the cpu measurement for the last hour

    1. Only where usage_user is greater than 50.0 and host is serverA (we expect two lines in a graph)
    2. For each host (we expect two lines on the graph per host)
    3. For the host, serverA, add usage_system and usage_user and put that result in a new column titled usage_system_and_user, while keeping usage_system and usage_user. (we expect three lines in the graph)
  3. Calculate the min, max, mean for used_percent for the mem measurement

    1. For the last hour for a host named serverA (we expect a tabular view)
    2. For each region, returning the value of each and the region name (we expect a tabular view)
    3. For a host named serverA in 5m buckets for the last 4h (we expect three lines in a graph)
    4. For each region in 5m buckets for the last 4h, returning the value, region name, and time (we expect three lines in the graph for each region)
  4. Get the rate in bytes per second from the bytes_in and bytes_out fields for the net measurement. These fields are counters that always increase except when they have a reset.

    1. For a host named serverA for the last 5 minutes (we expect two numbers to be displayed in single stat panes).
    2. For each host (we expect two stats per host in a tabular view)
    3. For each service (many hosts in a single service) (we expect two stats per service in a tabular view)
    4. Do i but in MB per minute for the last 4 hours with one point every 5m per line (we expect graphs with the same number of lines as stats as before)
    5. Do ii but in MB per minute for the last 4 hours with one point every 5m per line (we expect graphs with the same number of lines as stats as before)
    6. Do iii but in MB per minute for the last 4 hours with one point every 5m per line (we expect graphs with the same number of lines as stats as before)
  5. Calculate the error percentage per minute for the last hour from the http_requests_total measurement and the field value, where there is a tag named status that has a status code ranging from 200-500. Error percentage is defined as (rate of requests where status is 500) / (total rate of requests)

    1. For requests to host named serverA (we expect a single stat pane)
    2. For requests to each service (we expect a tabular view)
    3. Same as i, but in 5m windows for the last 4 hours (we expect a single line on a graph)
    4. Same as ii, but in 5m windows for the last 4 hours (we expect a line per service on a graph)
  6. Show 10 hosts using the most disk space (disk measurement and used_percent field)

    1. For the last hour (we expect a tabular view)
    2. Use those 10 hosts and get their disk space used over the last hour (we expect 10 lines on the graph representing the 10 hosts)

Supplemental Information for Alternative Ways to Represent Shortcut Syntax

As mentioned before, Flux is a functional language. That means the results of one operation can be forwarded to a function that can transform those results, reshape them, modify or insert new values, or join two separate tables (results) together. Let's look at what our shorthand syntax looks like in the full functional representation:

@my_data.h2o_temperature{location, state, surface_degrees}
// This is a comment because it follows // so it is ignored by the query engine
// The above query line becomes:
from(bucket: "my_data", measurement: "h2o_temperature", columns: ["location", "state", "surface_degrees"])

We've introduced comments, which follow anywhere in a line after //. This example only produces one function so it's not very instructive, but let's look at the from function for a moment. We can see from the example that Flux has named arguments. Named arguments can either be required or have default values. In the case of from, only bucket and measurement are required, which means it always returns data from a single measurement (which is why you can think of a measurement as a table). We'll look at how to join data from multiple measurements (or tables) in a later section.

Flux also supports positional arguments. The call to from above can also be written in the following two ways:

from("my_data", "h2o_temperature", columns: ["location", "state", "surface_degrees"])
// is equivalent to

from(bucket: "my_data", measurement: "h2o_temperature", columns: ["location", "state", "surface_degrees"])
// Because the definition of the from function has bucket, measurement, and columns as the first three arguements.
// There are others, which we'll introduce later

To show calling another function, let's look at getting the last value, but only for series in the state of CA:

@my_data.h2o_temperature{location, surface_degrees, state == "CA"}
// will map to this Flux functional code
from(bucket: "my_data", measurement: "h2o_temperature", columns: ["location", "state", "surface_degrees"])
    |> filter({state == "CA"})

We've introduced a number of new concepts here. From the top line, we can see that the last part of the Column Filter Predicate is a matcher of state == "CA". Matchers like this are always the last argument in the filter predicate. They can be any boolean expression and can be nested like (location == "platte_river" or location == "cherry_creek") and state == "CO". Notice also that in our shortcut syntax on the top line, we left state out of the list of columns that we want in the result, but that columns is still brought in because the matcher state == "CA" tells Flux to include it. That's why we see state included in the list of columns in our call to from (it has to be included for the call to filter to work).

In the matcher part of the filter predicate, the column identifier is always on the left hand side. This can either be wrapped in double quotes or not. We'll cover all of the available matching operators in a later section.

The next thing to notice is the pipe forward operator |>, which says, take the value returned from the function call to from and send that as the first argument into the filter function. The functional representation could be a one-liner (everything on a single line), but it's idiomatic to split function calls up on separate lines.

Another thing to note on the functional translation is how we're passing the filter predicate to the filter function. It's passed as a positional argument {state == "CA"} The following would be equivalent ways to get the same thing:

from(bucket: "my_data", measurement: "h2o_temperature", columns: ["location", "state", "surface_degrees"])
    |> filter(fn: {state == "CA"})

// is the same as
from(bucket: "my_data", measurement: "h2o_temperature")
    |> filter(fn: {"location", "surface_degrees", state == "CA"})
// Because columns is an optional argument to from and if left out, all columns will be included. We can
// also see that the filter predicate block includes the columns to filter down to

// is the same as
from(bucket: "my_data", measurement: "h2o_temperature", columns: ["location", "state", "surface_degrees"])
    |> filter(fn: (r) => r.state == "CA")
// in this case, we're not passing a filter predicate block, but instead an anonymous function, which
// won't change the columns in the result, rather it will only specify which rows to include

The last example shows Flux' anonymous function syntax. Don't worry if it looks strange to you, we'll come back to it later.

Finally, let's look at how we can get the last value for each series in a measurement where the series must have state == "CA", but only if that value appears in the last five minutes:

@my_data.h2o_temperature{location, state, surface_degrees, state == "CA" and _time > -5m}
  |> select(fn: last, by: ["_key"]) 

First, we're selecting the data we want to work with, which is the surface_degrees field from the h2o_temperature measurement for everything in the state of CA and we want all data from the last five minutes. From there we're passing the result to a new function select which takes arguments fn and by. The fn argument takes a function that can be applied to select rows in a grouping (in this case last). The by argument takes an array of column names to group rows by. In this case we group by _key because we want to get the last value for each series. We'll dig into the other grouping functions aggregate and transform and how to group by different columns and dimensions later in this guide.

Select can also be called with positional arugments like this: select(last, ["_key"]). Also, since the _key arugment for select has a default value of [_key], it can be called with just the function like this: select(last).

We expect the result set to look like this:

location state surface_degrees _key _time
coyote_creek CA 50.2 location=coyote_creek,state=CA 1600756160
santa_monica CA 63.6 location=santa_monica,state=CA 1600756160

The above query can also be represented in the full Flux functional notation like this:

from(bucket: "my_data", measurement: "h2o_temperature", columns: ["location", "state", "surface_degrees"])
    |> range(start: -5m)
    |> filter(fn: (r) => r.state == "CA")
    |> select(fn: last, by: ["_key"])

The range function operates explicitly on the _time column to limit results. Generally it's preferred to use the shortcut syntax when possible, but showing what the full translation to Flux functions has hopefully served as a gentle introduction to Flux functional concepts.

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