HTTP Proxy Cache Test

How well the proxy-enabled services such as OWA, Autodiscover, etc., proxy requests relies to a large extent on how the Exchange server caches are sized and utilized. Using the HTTP Proxy Cache test, administrators can monitor how each of these services use their caches, measures the size of every cache, and reports abnormalities in usage and size. This way, the bottlenecks to service performance are highlighted and a speedy resolution is enabled. 

Target of the test : A Microsoft Exchange 2013/2016 server

Agent deploying the test : An internal/remote agent

Outputs of the test : One set of results for each proxy-enabled service on the Exchange server monitored

Configurable parameters for the test
  1. Test period - How often should the test be executed
  2. Host - The host for which the test is to be configured.
  3. port – The port at which the host listens.
Measurements made by the test
Measurement Description Measurement Unit Interpretation

AnchorMailbox cache hit ratio:

Indicates the percentage of subscription requests to this service which resulted in AnchorMailbox cache hits since process start.

Percent

An X-AnchorMailbox is an HTTP header that is included in the initial subscription request from a client. It identifies the first mailbox in a group of mailboxes that share affinity with the same Mailbox server. Examples of AnchorMailbox identifiers are: SID, SMTP, Address, Organization name, Domain name, etc.

This header is essential to ensure affinity – i.e., to ensure the association of a sequence of request and response messages with a particular Mailbox server. The client triggers the creation of a cookie by including this header in the subscription request. The subscription response then contains the cookie. The client then sends that cookie in subsequent requests to ensure that the request is routed to the right Mailbox server.

A very low value for this measure indicates that the AnchorMailbox cache is utilized poorly. This could be owing to insufficient cache size, which typically renders the cache unable to hold many objects for lookup. Ineffective cache usage often leads to significant delays in request processing and adds to the processing overheads. 

Size of AnchorMailbox cache:

Indicates the current size of the AnchorMailbox cache of this service.

KB

A consistent rise in the value of this measure indicates that the cache is getting filled up with frequently-accessed objects. To ensure that these objects do not run out of space, you may have to allocate more space to the cache, increase the maximum size limit upto which the cache can grow, or remove unused items from the cache regularly.

AnchorMailbox to MailboxServer cookie hits:

Indicates the percentage of subscription requests to this service which leveraged the BEServer cookie to avoid database lookups since the process was restarted.

Percent

A high value is desired for this measure. A low value is indicative of very low cookie hits, which in turn implies that many costly  database lookups have occurred.

Database GUID MailboxServer cache hit ratio:

Indicates the percentage of requests to this service which resulted in DbGuid->MbxServer cache hits since process start.

Percent

A high value is desired for this measure.

Backend server cache refreshing queue length:

Indicates the length of the back end server cache refreshing queue of this service.

Number

 

Back end server cache size:

Indicates the current size of the back end cache of this service.

KB

A consistent rise in the value of this measure indicates that the cache is getting filled up with frequently-accessed objects. To ensure that these objects do not run out of space, you may have to allocate more space to the cache, increase the maximum size limit upto which the cache can grow, or remove unused items from the cache regularly.

FBA module key cache hit ratio:

Indicates the percentage of requests for this service that resulted in FBA module key cache hits.

Percent

Forms-based authentication (FBA) enables a sign-in page for Exchange Server 2013/2016 Outlook Web App that uses a cookie to store a user's encrypted sign-in credentials in the Internet browser. Tracking the use of this cookie enables the Exchange server to monitor the activity of Outlook Web App sessions on public and private computers. If a session is inactive for too long, the server blocks access until the user re-authenticates.

A high value is desired for this measure.

Size of FBA module key cache:

Indicates the current size of the FBA module key cache.

 

KB

A consistent rise in the value of this measure indicates that the cache is getting filled up with frequently-accessed objects. To ensure that these objects do not run out of space, you may have to allocate more space to the cache, increase the maximum size limit upto which the cache can grow, or remove unused items from the cache regularly.

Overall cache effectiveness:

Indicates the percentage of requests that leveraged client cookies or in-memory cache or both to avoid costly lookups since the process was started.

Percent

Ideally, the value of this measure should be over 80%. If not, check the values reported by the AnchorMailbox cache hit ratio, AnchorMailbox to MailboxServer cookie hits,DatabaseGUID to MailboxServer cache hit ratio, and FBA module key cache hit ratio measures to know which cache is poorly utilized and why.