> REINDEX is philosophically a maintenance command and a Postgres > extension not in the SQL standard, so it does not really qualify as a > DDL because it does not do in object definitions, so we could just > delete this comment. Or could it be more useful to consider that as a > special case and report it as a DDL, impacting log_statements?
It should be qualified just like CREATE INDEX. Both are not covered by the standard, which does not mention indexes, since they are an "implementation detail".
I think that it is pretty clear that CREATE INDEX should be considered DDL, since it defines (creates) and object. The same should apply to REINDEX.
Isn't REINDEX more like REFRESH MATERIALIZED VIEW and CLUSTER (especially without USING)?
CREATE INDEX (really, CREATE anything) is clearly DDL as it creates a new object, and DROP and ALTER are the same. But REINDEX just reaches below the abstraction and maintains the existing object without changing its definition.
I don't think whether it's in the standard is the controlling fact. It's not just DDL vs. not; there are naturally at least 3 categories: DDL, maintenance, and data modification.
Getting back to the question at hand, I think REINDEX should be treated the same as VACUUM and CLUSTER (without USING). So if and only if they are considered DDL for this purpose then REINDEX should be too.