Hi Per my post to the hackers list, here is a patch that renamed latestCompletedXid to latestCommittedXid, and updates it only on commits.
greetings, Florian Pflug
latestcommitted.patch.gz
Description: GNU Zip compressed data
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TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
