I've been thinking more about Gaetano Mendola's report of a FlushRelationBuffers failure during VACUUM FULL. I still don't see how that could happen in 7.4, but I do see a real related risk in 8.0.
Just another information that could help your analysis.
The index's parent is a table that implement a "materialized view" so is heavily updated by triggers.
Regards Gaetano Mendola
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