Sampling

Sampling at Ingest-Time​

Let’s say that you wanted to analyze and troubleshoot with highly verbose/voluminous data – for example, CDN logs, ELB Access Logs, or VPC Flows – but you were concerned about storage requirements and search performance. With Sampling, you can bring in enough samples that your analysis remains statistically significant, and also do all the necessary troubleshooting.

See the example below, or see more details in Access Logs and Firewall Logs.

Sampling Example​

Let’s use the out-of-the-box Sampling function to sample all events from sourcetype=='access_combined' where status is '200'. We’ll sample these at 5:1 (and all other events at 1:1). This should lower the volume of all verbose successes (200s), but still bring in all potentially erroneous events (400s, 500s, etc.) that can be used for troubleshooting.

• First, make sure you have a Route and Pipeline configured to match desired events.

• Next, let’s add a Regex Extract Function to extract the status field from _raw, and let’s call the resulting field __status. Remember, fields that start with __ are special fields in Cribl Stream, and can be used anywhere in a Pipeline.

Next, let’s add a Sampling function, and scope it to all events where sourcetype=='access_combined'. Let’s apply a filter condition of __status == 200, and a Sample Rate of 5.

To confirm that sampling works, compare the event count of all 200s before and after.

Each time an event goes through the Sampling function, an index-time sampled::<rate> field is added to it. You can use this field in your statistical functions, as necessary.