A tsidx file in Splunk is an index file that contains indexed data, and it consists of two main parts: a lexicon and a posting list (Option C). The lexicon is a list of unique terms found in the data, and the posting list is a list of references to the occurrences of these terms in the indexed data. This structure allows Splunk to efficiently search and retrieve data based on search terms.

In Splunk, common default time fields include date_minute, date_year, and date_day, which represent the minute, year, and day parts of event timestamps, respectively. date_zone (Option A) is not recognized as a common default time field in Splunk. The platform typically uses fields like _time and various date_* fields for time-related information but does not use date_zone as a standard time field.

Using report acceleration (Option C) is a performance improvement technique unique to dashboards in Splunk. Report acceleration involves pre-computing the results of a report (which can be a saved search or a dashboard panel) and storing these results in a summary index, allowing dashboards to load faster by retrieving the pre-computed data instead of running the full search each time. This technique is especially useful for dashboards that rely on complex searches or searches over large datasets.

To generate a summary index containing a count of events by productId, the correct search command would be | stats count by productId (Option A). This command aggregates the events by productId, counting the number of events for each unique productId value. The stats command is a fundamental Splunk command used for aggregation and summarization, making it suitable for creating summary data like counts by specific fields.

Search debug messages in Splunk appear in the Search Job Inspector while the search is running (Option C). The Search Job Inspector provides detailed information about a search job, including performance statistics, search job properties, and any messages or warnings generated during the search execution. This tool is invaluable for troubleshooting and optimizing searches, as it offers real-time insights into the search process and potential issues.