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Using REPLICA IDENTITY FULL on the publisher can lead to a full table scan per tuple change on the subscription when REPLICA IDENTITY or PK index is not available. This makes REPLICA IDENTITY FULL impractical to use apart from some small number of use cases. This patch allows using indexes other than PRIMARY KEY or REPLICA IDENTITY on the subscriber during apply of update/delete. The index that can be used must be a btree index, not a partial index, and it must have at least one column reference (i.e. cannot consist of only expressions). We can uplift these restrictions in the future. There is no smart mechanism to pick the index. If there is more than one index that satisfies these requirements, we just pick the first one. We discussed using some of the optimizer's low-level APIs for this but ruled it out as that can be a maintenance burden in the long run. This patch improves the performance in the vast majority of cases and the improvement is proportional to the amount of data in the table. However, there could be some regression in a small number of cases where the indexes have a lot of duplicate and dead rows. It was discussed that those are mostly impractical cases but we can provide a table or subscription level option to disable this feature if required. Author: Onder Kalaci, Amit Kapila Reviewed-by: Peter Smith, Shi yu, Hou Zhijie, Vignesh C, Kuroda Hayato, Amit Kapila Discussion: https://postgr.es/m/CACawEhVLqmAAyPXdHEPv1ssU2c=dqOniiGz7G73HfyS7+nGV4w@mail.gmail.com