Would it make sense, as suggested by Álvaro in the "CLOG contention" thread, to have a background process to set hint bits on tuples in dirty pages? Processing could be loosely based around the background writer techniques in terms of sweeping through the cache, but it would only look at dirty pages (destined to be written anyway) and I think we might want to further limit it to looking at tuples with an xmin or xmax value which precede the global xmin value and doesn't yet have a hint. It wouldn't do any writing; it would just check visibility and set hint bits. -Kevin
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