A quick question about web cache

[Former Member]

I've seen several clients in my lan trying to download patches and other programs like live messenger automatically, thats is not clear for me, why is not in the cache, how can i see what objects are in the web cache?, or how can i test that?

Thats downloads are consuming the 70% of my total bandwidth.

Regards

Esperanzaoo

[aloksard]

Hi Esperanzaoo,

Hope you are doing well.

MWG will only cache items under specific circumstances, the following at a minimum are required:-

-Response MUST contain at least one of the three header types: Cache-control, Expires or ETag

Yes caching of an object depends on server side.

Unfortunately their is no way to see contents of web cache partition at this moment .It's handled automatically by MWG. Currently there is no way the customer can influence it.

It is also to inform you that we also have a feature request regarding the same for viewing contents of web cache and deleting particular contents of web cache as per requirement.

This will be implemented in future releases MWG versions as per the decision taken by our product management team.

If I am not wrong in  version 7.7.x support for caching of HTTPS traffic is available.  You can check  if the response delivered to client from MWG has TCP_HIT  which means content is delivered from cache ( Example :- X-Cache: HIT from 10.54.173.220 can be seen in response being delievered to client)  and if you see TCP_MISS which means content is not delivered from cache.

MWG's web cache (if enabled) will write all content to the cache that is "cacheable", i.e., HTTP headers do allow caching, the request does not contain URL parameters, etc.
If you want to use advanced criteria (e.g. media type, size, url), use the policy rules to enable cache only for some requests.

Disk writing is done by OS, we currently use the deadline scheduler of Linux in MLOS.

The cache cleanup process is more advanced:
- if cache partition usage is < 70% => do not delete anything
- if usage is > 70%, read last usage of entries, for each chunk of found entries, remove the oldest ones.

As this strategy might be too slow for deletion in high performance environments, two addition strategies are applied:-

First, if cache usage is between 70% and 80%, we will bypass cache stores with probability 0-100% to prevent disk-full.

Second, if disk usage is too high, we will not look at least recently used time anymore, but just delete all entries we found.

This might look strange, but if you have millions of entries and delete some of them chosen uniformly at random, it is unlikely that you delete entries that were used recently.

Furthermore, we have some bypass options for the Web Cache if the IO load is too high, e.g., we limit the number of working threads doing IO simultaneously.

Regards

Alok Sarda

[aloksard]

Hi Esperanzaoo,

The duration how long the file is kept is up to MWG.

The webserver of cause can decide how long a cache is allowed to cache it, if it needs to be revalidated or something, but if for example the disk space is coming to an end MWG might still delete cache entries even if they could be kept longer.

Also, your access log can record Cache Status codes which can be pushed to CSR for reporting. The three status codes are as follows:

TCP_HIT for web cache hit
TCP_MISS_RELOAD for a miss
TCP_MISS_VERIFY if the data in the cache was outdated

The property in the access log would look like this:

String.ReplaceIfEquals (Cache.Status, "", "-")

You can also take  look at few options related to caching by taking MWG GUI access-> Navigate to Policy->Settings->Cache->Cache HTTP->Protcols and also Write Content to Cache even.

Regards

Alok Sarda

[aloksard]

Hi Esperanzaoo,

You can also take MWG GUI access-> Navigate to Dashboard tab->Charts & Tables->Web Cache Statistics and have a look.

Regards

Alok Sarda