c0f03aae04
When I consolidated two copies of the HOT-chain search logic in commit 4da99ea4231e3d8bbf28b666748c1028e7b7d665, I introduced a behavior change: the old code wouldn't necessarily traverse the entire chain, if the most recently returned tuple were updated while the HOT chain traversal is in progress. The new behavior seems more correct, but unfortunately, the code here relies on a scan with SnapshotNow failing to see its own updates. That seems pretty shaky even with the old HOT chain traversal behavior, since there's no guarantee that these updates will always be HOT, but it's trivial to broke a failure with the new HOT search logic. Fix by updating just the first matching pg_constraint tuple, rather than all of them, since there should be only one anyway. But since nobody has reproduced this failure on older versions, no back-patch for now. Report and test case by Alex Hunsaker; tablecmds.c changes by me.
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