Oracle X$ Tables

Oracle x$ "tables" are mostly instance or session memory structures presented as tables and serve as base tables of most v$ views. Entries in the following list are added one at a time in the course of my study of Oracle internals by reading books and online materials, through my own lab test, by interpreting the text in v$fixed_view_definition if available, or because other nice folks emailed me. Obviously there're much more tables in x$kqfdt and x$kqfta than listed below. But generally I omit those whose usage is not interesting or its meaning is too obvious.
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