Which argument to the | tstats command restricts the search to summarized data only?

The argument that restricts the search to summarized data only in the | tstats command is "summariesonly=t". This option specifically tells Splunk to return only results that come from summary indexing and to ignore any raw event data. This can significantly improve performance in scenarios where you are dealing with large datasets, as it reduces the amount of data processed, focusing only on pre-aggregated, summarized information that has already been indexed.

Using this option is particularly useful in security analytics where insights are derived from summarized events over a certain period rather than from all individual raw events. It enables users to quickly access relevant statistical insights and metrics without the overhead of processing large volumes of raw logs.

The other options do not serve this specific function of restricting search explicitly to summarized data, which is why "summariesonly=t" is the correct choice.