[horde] Database cleanup horde_histories

[Philipp Faeustlin]

Am 02.05.19 um 15:28 schrieb Michael J Rubinsky:
> 
> Quoting Jens Wahnes <wahnes at uni-koeln.de>:
> 
>> Michael J Rubinsky wrote:
>>> The history data doesn't really have anything to do with the 
>>> *display* of entries. If the entry in question still exists in the 
>>> application's backend storage, the entry will display fine. In 
>>> general, the history data is used for synchronization of things like 
>>> ActiveSync clients on a mobile device, or *DAV clients. If you don't 
>>> care about synchronization it is generally safe to delete this 
>>> information. Even if you do care about synchronization, it would 
>>> generally be safe to delete REALLY old entries - basically as long as 
>>> any clients you care about have synchronized since the history event 
>>> date, you should be fine.
>>
>> Thank you for explaining.
>>
>> I think the trouble really comes in when there are in fact entries of 
>> the kind I mentioned previously (e.g. monthly meeting entered into a 
>> group calendar by someone who has long left the workgroup). When the 
>> history records are incomplete, and there are members joining and 
>> leaving the workgroup all the time, there will be issues with syncing 
>> these recurring events (e.g. to mobile devices with reminders supposed 
>> to be popping up there).
> 
> I'm curious what kind of issues with syncing you see in this situation. 
> With regards to syncing, the history data is ONLY used to detect if an 
> entry has changed between two sync points. The actual data for the event 
> entry is stored in Kronolith, outside of the history system. As long as 
> the user has enough permissions to synchronize the shared calendar, 
> there should be no issue. When a new user is given permissions to a 
> calendar to sync, the complete calendar is synchronized at that time, 
> and the "sync point" of that state is saved in association with that 
> sync client. This is greatly simplified, but basically during sync the 
> history system is consulted to see if any entries have been added for 
> that calendar since the last sync-point the client knows about and the 
> current sync-point.  Anything outside of this window of time is 
> irrelevant for this user. So, basically, you can delete any history 
> entries that are older than the oldest sync-point a sync client is 
> associated with.
> 
> 
Is this correct?
There is no technical reason to keep horde_histories entries of deleted 
users?

Example:
I delete a user (testuser) by cli:
horde-remove-user-data testuser

Then I can clean up horde_histories for this user with no technical impacts.

SQL: Delete from horde_histories where history_who='testuser';

Will this SQL clear all the history entries of testuser?

>>
>>> Note that history data might have auditing value in your 
>>> organization, so that is also something to keep in mind as well.
>>
>> We're pretty much in the opposite situation. We must not keep records 
>> of personal data according to GDPR statutes, at least when these 
>> individuals are no longer affiliated with our organization. It's hard 
>> to meet these different goals at the same time, but still we strive to 
>> do our best -- any help how to improve this appreciated.
>>
>>
>> Jens
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> 
> 
> 
> 

-- 
Philipp Fäustlin


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