What does the following search do? sourcetype=access_combined | transaction JSESSIONID | timechart avg(duration)

The search provided is a valid Splunk search command that ultimately produces a timechart of the average duration of transactions identified by the JSESSIONID.

The first part of the search, which specifies sourcetype=access_combined, filters events down to those that match the defined access log format. Following this is the transaction command that groups these events based on the unique identifier, JSESSIONID. This grouping essentially captures all related events (or "transactions") tied to each session ID.

After defining the transactions, the search then utilizes the timechart command to plot the average duration of those transactions over time. The avg(duration) function calculates the average of the duration values for each group of events identified as a transaction, thereby creating a visual representation of how these durations fluctuate across the time span of the data included.

By chaining these commands properly, the search effectively analyzes and summarizes the data as intended, confirming its validity and illustrating the average duration in a timechart format.