This is not a trivial task. You can go to Settings->Indexes to see which app owns each index, but that doesn't necessarily limit where the index is used.
You could search for "index=foo" in all of your dashboards, alerts, and reports, but that would miss those where the index name is specified in a macro or eventtype. Including those still misses searches that use default indexes.
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If this reply helps you, Karma would be appreciated.
