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This patch reuses the existing aggtransspace in pg_aggregate to signal that an aggregate's transition state can grow unboundedly. If aggtransspace is set to a negative value, it now indicates that the transition state may consume unpredictable or large amounts of memory, such as in aggregates like array_agg or string_agg that accumulate input rows. This information can be used by the planner to avoid applying memory-sensitive optimizations (e.g., eager aggregation) when there is a risk of excessive memory usage during partial aggregation. Bump catalog version. Per idea from Robert Haas, though applied differently than originally suggested. Discussion: https://postgr.es/m/CA+TgmoYbkvYwLa+1vOP7RDY7kO2=A7rppoPusoRXe44VDOGBPg@mail.gmail.com