[openib-general] SA cache design

[Eitan Zahavi]

Hi Sean,

The issue is the number of queries grow by N^2. 
Only a very small subset of queries is used: 
* PathRecord by SRC-GUID,DST-GUID
* PortInfo by capability mask
Not to say the current implementations are perfect.
But RDBMS are optimized for other requirements not a simple single key
lookup.
Also, PathRecord implementation requires traversing the fabric.
One could store the result after enumerating the entire
N^2*Nsl*Np-key*...
But then lookup is a simple hash lookup.

Eitan
> 
> Brian Long wrote:
> > How much overhead is going to be incurred by using a standard RDBMS
> > instead of not caching anything?  I'm not completely familiar with
the
> > IB configurations that would benefit from the proposed SA cache, but
it
> > seems to me, adding a RDBMS to anything as fast as IB would actually
> > slow things down considerably.  Can an RDBMS + SA cache actually be
> > faster than no cache at all?
> 
> I'm not sure what the speed-up of any cache will be.  The SA maintains
a
> database of various related records - node records, path records,
service
> records, etc. and responds to queries.  This need doesn't go away.
The SA
> itself is perfect candidate to be implemented using a DBMS.  (And if
one had
> been implemented over a DBMS, I'm not even sure that we'd be talking
about
> scalability issues for only a few thousand nodes.  Is the perceived
lack of
> scalability of the SA a result of the architecture or the existing
implementations?)
> 
> My belief is that a DBMS will outperform anything that I could write
to store
> and retrieve these records.  Consider that a 4000 node cluster will
have about
> 8,000,000 path records.  Local caches can reduce this considerably (to
about
> 4000), and if we greatly restrict the type of queries that are
supported, then
> we can manage the retrieval of those records ourselves.
> 
> I do not want end-users to have to administer a database.  However, if
the user
> only needs to install a library, then this approach seems worth
pursuing.
> 
> - Sean
> _______________________________________________
> openib-general mailing list
> openib-general at openib.org
> http://openib.org/mailman/listinfo/openib-general
> 
> To unsubscribe, please visit
http://openib.org/mailman/listinfo/openib-general