[horde] Shortening Histories

[Ralf Lang]

Over the years, the Horde_Histories table can become quite large. It may 
make sense to sort out entries we won't need anymore

* Entries for users or items which have disappeared, been deleted 
outside of horde or directly on the backend
* Changes so far past that we don't care anymore

If I read the code correctly, ActiveSync completely relies on its own 
tables and does not need very old history entries.

The listBy code in Turba, Kronolith, Nag and Mnemo relies on histories 
to detect changes made at certain points or intervals in time

Imp optionally writes a mail creation log but I don't know if anything 
consumes it.

Will anything break if I delete far-past histories? I'd use code, not 
bare DB statements.

-- 
Ralf Lang
Linux Consultant / Developer
Tel.: +49-170-6381563
Mail: lang at b1-systems.de
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