Tool to rebuild history snapshots

[eastorski]

At this moment the only way to rebuild history snapshots is to generate them from scratch. This takes weeks to be finished.

It would be great if we have a tool which could help us with dev experiments or to migrate history snapshots if users don't want to resync

At least there is 2 things which we can not do without it:

1. rebuild already existing frozen history snapshots to remove duplicates
2. migrate snapshots to use enabled PageLevelCompression

[VBulikov]

AskAlexSharov added Imp2 as Importance