When do extracts run during the day?

When I was approached by the #WOW crew to provide a guest challenge, I was a little unsure as to what I could do. I primarily work as a Tableau Server admin, so rarely have a need to build dashboards (which is why I like to do the weekly #WOW challenges, to keep up my Desktop skills). Then the next day I was looking at a dashboard I’d built to monitor extracts on our Tableau Servers, and I thought it would be an ideal candidate for a challenge. I also thought it would provide any users of Tableau Server with the opportunity to implement this dashboard in their own organisation if they wished, by sharing with their Server Admins.

As a Tableau Server Admin, you get access to a set of ‘out of the box’ Admin views, one of which is called ‘Background Tasks for Extracts’ which gives you a view of when extracted data sources and workbooks run on the server. However while the provided view is fine if you want to quickly see what’s going on now, it’s not ideal if you want to see how things ran over a longer timeframe – it involves a lot of horizontal scrolling.

Many server admins will have ‘opened’ up access to the Tableau repository, the PostgreSQL database which stores a rich array of data, all about your Tableau Server [see here for further info], and enables admins to extend their analysis beyond the provided Admin views. This site even provides a set of pre-curated data sources to help you get started! These aren’t formally supported by Tableau, but is the brain-child of Matt Coles, a server admin at Tableau (no relation to me though!).

My dashboard doesn’t actually use one of these data sources though. For the challenge, I’ve just created some sample, anonymised data in the required structure. I’ll explain later at the end of the post how to go about converting this to use ‘real’ server data, if you do want to plug it into your own server environment.

Understanding the data

When using Tableau Server, published data sources and workbooks can connect to their underlying data source (eg a SQL Server database, an Excel file etc) directly (ie via a live connection) or via an extract. An extract means that a copy of the data is pulled from the underlying data source and stored on Tableau Server utilising Tableau’s ‘in memory’ engine when the data is then queried. An extract gets added to a schedule which dictates the time when the extract will get refreshed; this may be weekly, daily, hourly etc. Every time the extract runs, a background task is created which provides all the relevant details about that task. The data for this challenge provides 1 row for each extract task that was created between Monday 11th Jan 2021 and Friday 5th Feb 2021. The key fields of note are:

  • Id – uniquely identifies a task
  • Created At – when the task was created
  • Started At – when the task actually started running (if too many tasks are set to run at the same time, they will queue until the server resources are available to execute them).
  • Completed At – when the task finished, will be NULL if task hasn’t finished.
  • Finish Code – indicates the completion status of the job (0=success, 1=failed, 2= cancelled)
  • Progress – supposed to define the % complete, but has been observed to only ever contain 0 or 100, where 100 is complete.
  • Title – the name of the extract
  • Site – the name of the site on the server the extract is associated to

Based on the Finish Code and Progress, I have derived a calculated field to determine the state of the extract (to be honest, I think this is a definition I have inherited from closer analysis of the Background Tasks for Extracts Server Admin view, so am trusting Tableau with the logic).

Extract Status

IF [Finish Code] = 1 AND [Progress] <> 100 THEN ‘In Progress’
ELSEIF [Finish Code] = 0 AND NOT [Progress] = 1 THEN ‘Success’
ELSE ‘Failed’
END

Building the required calculated fields

The intention when being used ‘in real life’, is to have visibility of what’s going on ‘Now’ as well as how extracts over the previous few days have performed. As we’re working with static data, we need to hardcode what ‘Now’ is. I’ll use a parameter for this, so that in the event you do choose to plug this into your own server, you only have to replace any reference to the Now parameter with the function NOW().

Now

Datetime parameter defaulted to 05 Feb 2021 16:30

The chart we are going to build is a Gantt chart, with 1 bar related to the waiting time of the task, and 1 bar related to the running time of the task. We only have the dates, so need to work out the duration of both of these. These need to be calculated as a proportion of 1 day, since that is what the timeframe is displayed over.

Waiting Time

(DATEDIFF(‘second’, [Created At], IF ISNULL(Started At]) THEN [Now] ELSE [Started At ] END))/86400

Find the difference in seconds, between the create time and start time (or Now, if the task hasn’t yet started), and divide by 86400 which is the number of seconds in a day.

We repeat this for the processing/running time, but this time comparing the start time with the completed time.

Processing Time

(DATEDIFF(‘second’, [Started At], IF ISNULL([Completed At]) THEN [Now] ELSE [Completed At] END))/86400

As mentioned the timeframe we’re displaying over is a 24 hr period, and we want to display the different days over multiple rows, rather than on a single continuous time axis spanning several days.

To achieve this, we need to ‘baseline’ or ‘normalise’ the Created At field to be the exact same day for all the rows of data, but the time of day needs to reflect the actual Created At time . This technique to shift the dates to the same date, is described in this Tableau Knowledge Base article.

Created At Baseline

DATEADD(‘day’, DATEDIFF(‘day’, [Created At], #2021-01-01#), [Created At])

And again, we’re going to need to do a similar thing with the Started At field

Started At Baseline

DATEADD(‘day’, DATEDIFF(‘day’, [Started At], #2021-01-01#), [Started At])

Putting this out into a table, you can see what this data all looks like (note, I’m just choosing a arbitrary date of 01 Jan 2021, so my baseline dates are all on this date:

Building the Gantt chart

We’re going to build a dual axis Gantt chart for this.

  • Add Site to Rows
  • Add Title to Rows
  • Add Created At to Rows. Set it to the day/month/year level and set to be discrete (ie blue pill). Format the field to custom format of ddd dd mmm yyyy so it displays like Mon 11 Jan 2021 etc
  • Add Created At Baseline to Columns, set to exact date
  • Add Waiting Time (Avg) to Size and adjust to be thin

This will automatically create a Gantt chart view

Next

  • Add Started At Baseline to Columns, set to exact date, and move so the pill is now placed to the right of the Created At Baseline pill
  • On the Started At Baseline marks card, remove Waiting Time and add Processing Time (Avg) to the Size shelf instead. Adjust so the size is thicker.
  • Set the chart to be dual axis and synchronise the axes

The thicker bars based on the Started At / Processing Time need to be coloured based on Extract Status. Add this field to the Colour shelf of the Started At Baseline marks card and adjust accordingly.

The thinner bars based on the Created At / Waiting Time need to be coloured based on how long the wait time is (over 10 mins or not).

Over Wait Time Threshold

[Waiting Time] > 0.007

0.007 represents 10 mins as a proportion of the number of minutes in a day (10 / (60*24) ).

Add this field to the Colour shelf of the Created At Baseline marks card and adjust accordingly (I chose to set to the same red/grey values used to colour the other bars, but set the transparency of these bars to 50%).

Formatting the Tooltips

The tooltip for the Waiting Time bar displays

The Created At Baseline and Started At Baseline should both be added to the Tooltip shelf and then custom formatted to h:mm am/pm

The Waiting Time needs to be custom formatted to hh:mm:ss

The tooltip for the Processing Time bar is similar but there are small differences in the display,

Formatting the axes

The dates on the axes are displayed as time in am/pm format.

To set this, the Created At Baseline / Started At Baseline pills on the Columns shelf need to be formatted to h:mm am/pm

Adding the reference band

The reference band is used to highlight core working hours between 8am and 5pm. Right click on the Created At Baseline axis and Add Reference Line. Create a reference band using constants, and set the fill colour accordingly.

Apply further formatting to suit – adjust sizes of fonts, add vertical gridlines, hide column/axes titles.

Filtering the dates displayed

As discussed above, when using this chart in my day to day job, I’d be looking at the data ‘Now’. As a consequence I can simply use a relative date quick filter on the Started At field, which I default to Last 7 days.

However, as this challenge is based on static data, we need to craft this functionality slightly differently.

We’re only going to show up to 10 days worth of data, and will drive this using a parameter.

pDaysToShow

An integer parameter, ranging from 1 to 10, defaulted to 7, and formatted to display with a suffix of ‘ days’.

We then need a calculated field to use to filter the dates

Filter : Days to Show

DATETRUNC(‘day’,[Created At]) >= DATEADD(‘day’,([pDaysToShow]-1)*-1,DATETRUNC(‘day’,[Now]))

Add this to the Filter shelf and set to True.

Additionally, the chart can be filtered by Site, so add this to the Filter shelf too.

Building the Key legend

Some people may build this by adding a separate data source, but I’m just going to work with the data we have. This technique is reliant on knowing your data well and whether it will always exist.

On a new sheet, add Site to the Filter shelf and filter to sites 7 and 9.

Create a new field

Key Label

If [Site] = ‘Site 9’ THEN ‘Waiting’ ELSE ‘Processing’ END

and add this to the Columns shelf and sort the field descending, so Waiting is listed before Processing.

Alongside this field, type directly into the Columns shelf MIN(1).

Edit the axes to be fixed to from 0 to 1. Then add the Site field to the Colour shelf and also to the Size shelf and adjust accordingly (you may need to reverse the sizes). I lightened the colour by changing the opacity to 50%.

Now hide the axes, remove row & column borders, hide the column title and turn off tooltips.

The information can all now be added to a dashboard.

Using your own data

To use this chart with your own Tableau Server instance, you need to create a data source against the Tableau postgres repository that connects to the _background_tasks (bgt) table with an inner join to the _sites (s) table on bgt.site_id = s.Id. Rename the name field from the _sites table to Site. If you don’t use multiple sites on your Tableau Server instance, then the join is not required. The sole purpose of the join is to get the actual name of the site to use in the display/filter.

You should then be able to repoint the data source from the Excel sheet to the postgres connection. You may find you need to readjust some of the colours though.

When I run this, I’m using a live connection so I can see what is happening at the point of viewing, rather than using a scheduled extract. To help with this, I add a data source filter to limit the days of data to return from the query (eg Created at <=10 days), which significantly reduces the data volume returned with a live connection.

Hopefully you enjoyed this ‘real world’ challenge, and your server admins are singing your praises over the brilliance of this dashboard 🙂

My published version is here.

If you’ve got any feedback or suggestions on improvements to enhance the viz even further, please do let me know.

Happy vizzin’! Stay safe!

Donna

3 thoughts on “When do extracts run during the day?

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