[pbs-devel] [PATCH proxmox-backup 4/4] docs: add description for gc-cache-capacity tuning parameter

[Christian Ebner]

On 4/4/25 13:58, Lukas Wagner wrote:
> 
> 
> On  2025-04-03 14:27, Christian Ebner wrote:
>> Adds a bullet point to the listed datastore tuning parameters,
>> describing its functionality, implications and typical values.
>>
>> Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
>> ---
>>   docs/storage.rst | 12 ++++++++++--
>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/docs/storage.rst b/docs/storage.rst
>> index 490302955..cab65ef79 100644
>> --- a/docs/storage.rst
>> +++ b/docs/storage.rst
>> @@ -435,9 +435,17 @@ There are some tuning related options for the datastore that are more advanced:
>>   
>>     This can be set with:
>>   
>> -.. code-block:: console
>> +  .. code-block:: console
>> +
>> +    # proxmox-backup-manager datastore update <storename> --tuning 'sync-level=filesystem'
>>   
>> -  # proxmox-backup-manager datastore update <storename> --tuning 'sync-level=filesystem'
>> +* ``gc-cache-capacity``: Datastore GC least recently used cache capacity:
>> +  Allows to control the cache capacity used to keep track of chunks for which
>> +  the access time has already been updated during phase 1 of garbage collection.
>> +  This avoids multiple updates and increases GC runtime performance. The
>> +  capacity is set as the given value multiplied by 1024. Higher values can
>> +  reduce GC runtime at the cost of increase memory usage, setting the value to 0
>> +  disables caching.
> 
> I think we could completely omit the "the capacity is set as the given value multiplied by 1024" sentence here
> and consider the fact that the LRU cache size is value * 1024 an implementation detail.
> For the user, the exact number of cached digests in the backend is probably not really that important, right?

Agreed, I opted for including this as the option states "capacity", so 
one might expect the exact capacity. But you are completely right that 
this is mostly unimportant for the end user.

> In reality, they just want some knob that they can adjust in a range from 0 (no caching) to some maximum.
> 
> Same of course applies also for the GUI patch and the log message.
> 
> What do you think?

Will send a new version which drops the mentions of multiples of 1024, 
thanks for review and testing!