Good afternoon!
During pg_upgrade migration, the pg_commit_ts directory is not copied when track_commit_timestamp = on is set. There is a patch in the attachment that fixes this.
Contents & Purpose
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The patch copies the pg_commit_ts directory of the old cluster and updates the Latest checkpoints oldestCommitTsXid and Latest checkpoint's newestCommitTsXid for the new cluster. If required.
Initial Run
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The patch can be applied on the master branch.
I don't understand what tests are needed for such a patch. The patch is very simple.
Performance
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The pg_upgrade operation time increases by the time the pg_commit_ts catalog is copied.