How to Split your Data Into A Fixed Amount of Buckets

Okay, another question from Twitter (original content will have to wait till I get some more free time!)

Here’s the challenge:

So what we need to do here is somehow infer the time-range of the query, and then create a fixed set of time bins according to that range.

I think the only way to that is by performing 2 queries – one to get the time range and convert it into a fixed interval, and a second query with the actual logic.

To convert the result of the first query into a ‘variable’ we can use in the second query, I’ll use the ‘toscalar‘ operation.

Here we go:

let numberOfBuckets = 24;
let interval = toscalar(requests
| summarize interval = (max(timestamp)-min(timestamp)) / numberOfBuckets
| project floor(interval, 1m));
| summarize count() by bin(timestamp , interval)

I use ‘floor’ here just to round the interval and make the results a bit more readable.

Back-fill Missing Dates With Zeros in a Time Chart

A common ask I’ve heard from several users, is the ability to fill gaps in your data in Kusto/App Analytics/DataExplorer (lots of names these days!):

If your data has gaps in time in it, the default behavior for App Analytics is to “connect the dots”, and not really reflect that there was no data in these times. In lots of cases we’d like to fill these missing dates with zeros.

The way to go to handle this, is to use the “make-series” operator. This operator exists to enable advanced time-series analysis on your data, but we’ll just use it for the simple use-case of adding missing dates with a “0” value.

Some added sophistication is converting the series back to a *regular* summarize using “mvexpand”, so we can continue to transform the data as usual.

Here’s the query (Thanks Tom for helping refine this query!) :

let start=floor(ago(3d), 1d);
let end=floor(now(), 1d);
let interval=5m;
| where timestamp > start
| make-series counter=count() default=0 
              on timestamp in range(start, end, interval)
| mvexpand timestamp, counter
| project todatetime(timestamp), toint(counter)
| render timechart


Searching all Tables with Union, Searching all Fields with ‘*’

One of the major use cases for log analytics is root cause investigation. For this, many times you just want to look at all your data, and find records that relate to a specific session, operation, or error. I already showed one way you can do this using ‘search’, but I want to show how you can do this using ‘union *‘ which is a more versatile.

union *
| where timestamp > ago(1d)
| where operation_Id contains '7'
| project timestamp, operation_Id, name, message

In fact I already used ‘union *’ when I wanted to count users across all tables.
Another useful tool is searching across all fields – you can do this with ‘where *‘:

union *
| where timestamp > ago(1d)
| where * contains 'error'
| project timestamp, operation_Id, name, message

This is really powerful, and can be used to basically do a full table scan across all your data.
But one thing that always annoyed me is that you never know which table the data came from. I just discovered a really easy way to get this – using the ‘withsource’ qualifier:

union withsource=sourceTable *
| where timestamp > ago(1d)
| where * contains 'error'
| project sourceTable, timestamp, operation_Id, name, message

Cross App Queries in Azure Log Analytics

I’ll keep it short and simple this time. Here’s a great way to debug your app across multiple App Insights instances.

So, I have two Azure Functions services running, with one serving as an API, and the other serving as BE processing engine. Both report telemetry to App Insights (different apps), and I am passing a context along from one to the other – so I can correlate exceptions and bugs.

Wouldn’t it be great to be able to see what happened in a single session across the 2 apps?

It’s possible – using ‘app‘ – just plugin the name of the app insights resource you want to query, and a simple ‘union‘.

Here you go:

let session="reReYiRu";
union app('FE-prod').traces, app('BE-prod').traces
| where session_Id == session 
| project timestamp, session_Id, appName, message
| order by timestamp asc 


Don’t forget –

  1. You can use the field ‘appName‘ to see which app this particular trace is coming from.
  2. Different machines have different times.. Don’t count on the timestamp ordering to always be correct.

A Simple Way to Extract Data From Traces – ‘Parse’

There is a nifty little operator in Azure Log Analytics that has really simplified how I  work with regular expressions – It’s called “parse” and I’ll explain it through a little example.

Let’s say you have a service that emits traces like:

| where message contains "Error"
| project message

11:07 Error-failed to connect to DB(code: 100)

12:02 Error-failed to connect to DB(code: 100)

12:05 Error-query failed on syntax(code: 355)

12:06 Error-query failed on timeout(code: 567)

I’d like to count how many errors I have from each code, and then put the whole thing on a timechart that I can add to my dashboard, in order to monitor errors in my service.

Obviously I’d like to extract the error code from the trace, so I need a regular expression.

Well, if you’re anything like me the first thing you’ll do is start feverishly googling regular expressions to try to remember how the heck to do it… and then flailing for like an hour until getting it right.

Well, using parse, things are much much easier:

| where message contains "Error"
| parse message with * "(code: " errorCode ")" *
| project errorCode


And from here summarizing is just a breeze:

| where message contains "Error"
| parse message with * "(code: " errorCode ")" *
| summarize count() by errorCode, bin(timestamp, 1h)
| render areachart kind=stacked

Happy parsing!

Using Azure Log Analytics to Calculate User Engagement Metrics

Engagement/Usage metrics are some of the most commonly used, yet tricky to calculate metrics out there. I myself have seen just about 17 different ways to calculate stickiness, churn, etc. in analytics – each with its own drawbacks, all of them complex and hard to understand.

I’ve touched on this subject before when I offered a query for stickiness, but

  1. It was complex and convoluted (yes, I’ll admit it!)
  2. Hyper-log-log (hll) has known limitations in precision, especially when dealing with small numbers.

I’m really glad to showcase some new capabilities in Azure Log Analytics that super-simplify everything about these metrics. These are the new operators:

evaluate activity_engagement(...)
evaluate activity_metrics(...)

I really won’t babble too much here, there’s official documentation for that. But the basic concept is so easy you should really just try it out for yourself.

First, stickiness (rolling dau/mau). So, so simple:

union *
| where timestamp > ago(90d)
| evaluate activity_engagement(user_Id, timestamp, 1d, 28d)
| project timestamp, Dau_Mau=activity_ratio*100 
| where timestamp > ago(62d) // remove tail with partial data
| render timechart 

Churn + Retention rate (week over week):

union *
| where timestamp > ago(90d)
| evaluate activity_metrics(user_Id , timestamp, 7d)
| project timestamp , retention_rate, churn_rate
| where retention_rate > 0 and 
  timestamp < ago(7d) and timestamp > ago(83d) // remove partial data in tail and head
| render timechart

Even cooler – you can add dimensions to slice your usage data accordingly. Here is a chart of my apps’ retention rates for different versions of the chrome browser:

union *
| where timestamp > ago(90d)
| where client_Browser startswith "chrome" 
| evaluate activity_metrics(user_Id , timestamp, 7d, client_Browser   )
| where dcount_values > 3
| project timestamp , retention_rate, client_Browser 
| where retention_rate > 0 and 
  timestamp < ago(7d) and timestamp > ago(83d) // remove partial data in tail and head
| render timechart


Search in App Analytics

The questions I get most often about Analytics aren’t usually about super-complicated queries or magic ML functions.

It’s usually just about how to find specific logs in an investigation.

App Insights Analytics has a really simple way to do it – search. This will search for a keyword across all your tables, across all columns.

search "Error"

If you look at the results, the first column is called $table – it is the name of the table from which the results came from.

You can combine search with a summarize, or any other filter you need:

search "Error" 
| summarize count() by bin(timestamp, 1h)
| render timechart  

It’s also possible to search in specific tables:

search "fail" in (customEvents, dependencies)

Happy searching!