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RE: Bug 4558: Scalability and performance problems with expressing allowable nested policy assertions

From: Asir Vedamuthu <asirveda@microsoft.com>
Date: Wed, 16 May 2007 18:35:33 -0700
To: David Orchard <dorchard@bea.com>, "public-ws-policy@w3.org" <public-ws-policy@w3.org>
Message-ID: <C9BF0238EED3634BA1866AEF14C7A9E543152A4EE9@NA-EXMSG-C116.redmond.corp.microsoft.com>

>The scalability problem is that it may be difficult to list and
>exchange all the possible nested assertions.
>The performance problem is that such a scale may result in slow policy
>processers performing intersection.

We are not sure that a provider or requester will support the myriad of options that will result in a large number of possible combinations that one should be worried about. We cannot imagine a practical scenario where a provider or requestor would expose a myriad of options using the X509 assertion. We think a provider or requester allows little variability (that reflects what is wired under the hood) and publishes one or some small number of policy alternatives.

Having said that, we do not actually see a large number of possible combinations as a problem. While a na´ve implementation would, we suppose, do the full expansion to normal form of all policy alternatives and then perform n-squared matching. Please note that there are many opportunities exist for optimization.

OTOH, if you are concerned about malicious providers ... Malicious providers may provide a policy expression with a large number of alternatives, a large number of assertions in alternatives or deeply nested policy expressions. Just like any quality web service implementation has throttling knobs to limit the size of the message and other message related parameters, policy implementers need to anticipate these rogue providers and use a configurable bound with defaults on number of policy alternatives, number of assertions in an alternative, depth of nested policy expressions, etc.

Regards,

Asir S Vedamuthu
Microsoft Corporation


-----Original Message-----
From: public-ws-policy-request@w3.org [mailto:public-ws-policy-request@w3.org] On Behalf Of David Orchard
Sent: Tuesday, May 15, 2007 5:26 PM
To: public-ws-policy@w3.org
Subject: Bug 4558: Scalability and performance problems with expressing allowable nested policy assertions


The policy intersection algorithm results in policy assertions with
nesting to
be verbosely expressed with all of the possible nested assertions marked
as
optional="true".  One example of this is SecurityPolicy with X509,
detailed in
http://lists.w3.org/Archives/Public/public-ws-policy/2007May/0160.html.


The scalability problem is that it may be difficult to list and exchange
all
the possible nested assertions.  The performance problem is that such a
scale
may result in slow policy processers performing intersection.

One counter-arguments are that the number of nested assertions is not
large
enough to warrant this optimization, and that the optimization of adding
optional="true" is sufficient.  The general argument of premature
optimization
applies.  This would be a close with no action or defer to v.Next.

Proposal 1:
Update the policy intersection algorithm so that an empty policy
assertion
matches a policy assertion with a nested assertion resulting an the same
policy
assertion with a nested assertion.

Proposal 2:
Provide an explicit wildcard to match any nested assertions.
Received on Thursday, 17 May 2007 01:35:46 UTC

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