Heikki Linnakangas wrote:
That's a pretty sensitive tradeoff, we want to prune often to cut the
long HOT chains, but not too often because it's pretty expensive to
acquire the vacuum lock and move tuples around. I don't think we've
found the optimal solution yet. Separating the pruning and defragmenting
might help.

Does defragmenting force writing a full page image to the WAL afterwards?
Or does it just log the fact that the page was defragmented, and the actual
work is redone on recovery?

In the first case, over-zealous defragmenting might be costly in terms of
WAL traffic too, not only in term of CPU usage.

greetings, Florian Pflug

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