Hello Hayato,
> WaitForOlderSnapshots() waits other transactions which can access older tuples
> than the specified (=current) transaction, right? I think it does not solve our issue.
Oh, I actually described the idea a bit incorrectly. The goal isn’t simply to call WaitForOlderSnapshots(slot.xmin);
rather, it’s to ensure that we wait for slot.xmin in the same way we wait for regular snapshots (xmin).
The reason WaitForOlderSnapshots is used in ReindexConcurrently and DefineIndex is to guarantee that any transaction
needing to view rows not included in the index has completed before the index is marked as valid.
The same logic should apply here — we need to wait for the xmin of slot used in conflict detection as well.
> From another point of view... this approach must fix REINDEX code, but we should
> not modify other component of codes as much as possible. This feature is related
> with the replication so that changes should be closed within the replication subdir.
One possible solution here would be to register a snapshot with slot.xmin for the worker backend.
This way, WaitForOlderSnapshots will account for it.
By the way, WaitForOlderSnapshots is also used in partitioning and other areas for similar reasons,
so these might be good places to check for any related issues.
Best regards,
Mikhail,
