[sr-dev] git:master: modules_k/presence Fixed DB Storage Modes

[Anca Vamanu]

On 02/20/2012 01:47 PM, Klaus Darilion wrote:
>
>> I see now an opportunity to improve the performance because of this
>> behavior - having a mode in which to read from memory for Subscribes,
>> but always read from DB for Publishes.
> What if publ_cache=1. What really happens on incoming PUBLISH?
>
> I have not read the code but I suspect with subs_db_mode=3 and
> publ_cache=0 the module does (without permissions checking):
>
> incoming PUBLISH without e-tag:
> INSERT INTO presentity .....
>
> incoming PUBLISH with e-tag:
add here query to verify if the publish record exists:
SELECT * FROM presentity WHERE etag=..
> UPDATE presentity ... WHERE etag='..' AND ......
>
> incoming SUBSCRIBE without to-tag:
> INSERT INTO active-watchers ...
> SELECT * FROM presentity WHERE ....
>
> incoming SUBSCRIBE with to-tag:
add there the query to verify if the subscribe dialog exists:
     SELECT * FROM active_watchers WHERE ..
> UPDATE active-watchers ...
> SELECT * FROM presentity WHERE ....
>
And you have all the operations that are performed with with 
subs_db_mode=3 and publ_cache=0;

> So what changes if publ_cache=1?

If publ_cache=1 the performance improvement happens  when a Subscribe 
comes. Before doing the query in the presentity table, a check in the 
publish cache is made to see if there are any known active publications 
for that presentity. This way the query in presentity table is made only 
when there is something to retrieve from there.

This could be extended to help with the read query when a Publish with 
e-tag comes. Now the etag is not stored in cache, only the presentity uri.

Regards,
Anca

> thanks
> Klaus
>
>
>
>> Regards,
>> Anca
>>
>>> thanks
>>> Klaus