The Search Job Inspector is the primary tool for diagnosing the performance of a specific search job. In a distributed environment with an indexer cluster, it provides detailed performance metrics on a per-indexer (peer) basis. This allows an administrator to see how many events each indexer scanned, how much time each indexer spent on the search, and other key statistics. By examining this per-peer data, one can identify "straggler" indexers or data distribution imbalances that are causing the overall search to perform slowly, directly addressing the customer's concern.

B. The Search Job Inspector is a diagnostic tool for analyzing job execution; it does not include a "Search Health Check" feature that automatically provides an optimized version of the SPL query.

C. This is incorrect. The Search Job Inspector is the designated and most effective tool for troubleshooting the performance of a single, specific search job in real-time or after completion.

D. The question does not state that the transaction command is being used. This option makes an unsubstantiated assumption and fails to answer how the Search Job Inspector would be used.

1. Splunk Enterprise Documentation, Search Manual, "Use the Search Job Inspector": This document details the functionality of the Search Job Inspector. The section "View search process activity on the search peers" explicitly states: "The Search Job Inspector shows you information about the search process on each of the search peers that participated in the search." It lists available fields for each peer, including duration (time spent) and scannedCount (events processed), which directly supports the correct answer.

2. Splunk Enterprise Documentation, Search Manual, "Execution costs": This section describes how the inspector breaks down the cost of the search by component. It notes, "For each search processor, see the number of events that the processor read from disk, and the number of events that the processor returned." This confirms the inspector's ability to provide per-component statistics, which in a distributed search includes the individual indexers.