loadFrxAjax has high CPU and IO impact

The loadFrxAjax request is slow and insufficiently cached. It can make several copies of the content for the sake of low-memory diffing, which it sometimes recalculates. This results in high IO load as well as high CPU use.

The performance is worse the larger the file and the more revisions of the file in the review.

This may only be a problem when using Storing all the revisions under review. We need to test that.

This seems to be a somewhat recent regression in 3.4.4. E.g. it's been noticed a bit in 3.4.4 by one customer who has experienced performance degradation since 2.10 and an internal instance that has also had hardware changes.

Initial investigation yielded various specific performance issues but none that explained a regression.