[horde] Shortening Histories

[Ralf Lang]

On 09.01.2017 23:49, Michael J Rubinsky wrote:
>
> Quoting Jan Schneider <jan at horde.org>:
>
>> Zitat von Ralf Lang <lang at b1-systems.de>:
>>
>>> 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
>
> On the contrary, I would argue we should technically do the opposite and
> create History entries for items that have been deleted outside of Horde
> or directly on the backend so that Horde can be made aware of it. In
> fact, this has come up recently on the ML, or maybe it was in an
> enhancement request. Of course doing so is no easy task.

I think I understand the intention behind this. Shareable and syncable 
resources deleted by outside should also create the necessary 
information to do the necessary to any client connector.

>
>>> * Changes so far past that we don't care anymore
>
> I wouldn't object to some configuration that would allow the table to be
> trimmed after some configurable time (probably measured in years) but
> there would need to be a pretty loud warning on the configuration page
> that this could lead to changes being missed by sync clients.

It was only something I wanted to apply to a specific installation.

It should not be a default horde behaviour. Still, there should be some 
way to make sure rarely-read histories don't slow down access to 
histories which are more interesting. I am not sure at the moment:

* Delegate this task to the DB administrator to solve this in 
db-specific ways, i.e. table partitions by date field value so indexes 
and searches won't be affected in most cases.

* Provide some optional lru caching for Histories -> Horde_Cache, 
Horde_Hashtable

* Allow filtering changes that would not affect the most recent state 
(an object that has been created and deleted years before now) -> still 
destroys undo/undelete for very old items and sync for clients with a 
very old last sync.

>
>
>>> Will anything break if I delete far-past histories? I'd use code, not
>>> bare DB statements.
>
> As Jan mentioned, sync clients would not receive any changes if they
> have not yet synced the changes you delete. Additionally, IMP uses
> History to write the Maillog - which stores things like if/when a
> message was responded to etc... So if a message still exists and you
> remove those entries you loose this trail.
>


-- 
Ralf Lang
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