The name collision happens when the name of the new partition is the same as
the name of one of the merging partitions. Currently, ATExecMergePartitions()
first gives the new partition a temporary name and then renames it when old
partitions are deleted. That negatively influences the naming of related
objects like indexes and constrains, which could inherit a temporary name.
This commit changes the implementation in the following way. A merging
partition gets renamed first, then the new partition is created with the
right name immediately. This resolves the issue of the naming of related
objects.
Reported-by: Alexander Lakhin
Discussion: https://postgr.es/m/edfbd846-dcc1-42d1-ac26-715691b687d3%40postgrespro.ru
Author: Dmitry Koval, Alexander Korotkov
Reviewed-by: Robert Haas, Justin Pryzby, Pavel Borisov
885742b9f8