- To Store frequently used data in memory.
- 1st Time will get from DB and retain a copy in memory. Any request during duration will get from cache.
- After duration, the next request will get from DB again and cache for another duration.
- Improve the performance and scalability.
- VaryByParam="None" , a seperate response is cached for GET and POST request, that's why when you change drop down (POST), it will keep showing back same selection.
- Disadvantage: cached pages that display results can be inconsistent, i.e. not reflecting the latest changes applied to a database.
1)Output Caching
- Store a copy rendered HTML pages to the client.
<%@ OutputCache Duration="10"//Second
VaryByParam="ddlProducts" //No use then None
Location="ServerAndClient" //Where the cache store %>
OR Code Behind :
Response.Cache.SetExpires(DateTime.Now.AddSeconds(30));
Response.Cache.SetCacheability(HttpCacheability.Public);
Response.Cache.SetValidUntilExpires(true);
Response.Cache.VaryByParams["ddlProducts"] = true;
2)Fragment Chaching
- partial Caching use for specific section of page is static and take long time to load. Others is process like normal. E.g. past 10 year total sales.
- Use in UserControl
- "Shared = true" attribute in OutputCache only for userControl, it allow many web forms share a single userControl.
Steps :
- Encapsulate specific sections of that page put into userControl.
- Use OutputCache directive on that userControl to specify the cache settings.
- Drag and drop the userControl on the webform.
VaryByParam
|
Description
|
none
|
only GET
|
*
|
n versions of page cached based on query string and/or POST
body
-can be user control or QueryString
|
V1
|
n versions of page cached based on value of V1
variable in query string or POST body
|
V1;V2
|
n versions of page cached based on value of V1 and V2
variables in query string or POST body
|
- VaryByHeader - maintain separate cache entry for header string changes (UserAgent, UserLanguage, etc.)
- VaryByControl - for user controls, maintain separate cache entry for properties of a user control
- VaryByCustom - can specify separate cache entries for browser types and version or provide a custom GetVaryByCustomString method in HttpApplication derived class.
3)Data Caching
- Store data in cache. Just Query DB 1 time.
- Cache will be remove when expired, full, dependency object change.
- Cache can set expired, but Application Cannot.
- AbsoluteExpiration : when should be remove the cache
- SlidingExpiration : How long data remain in cache after the data was last accessed.
- You will get run-time error if sepicy AbsoluteExpiration and SlidingExpiration .
- CacheItemPirority : If server memory full, cache may removed. So this 1 is to specified the priority of cache.
- Add and Insert is same. Different : If Cache already have, add is not work, but insert will overwrite the Cache.
- CacheItemRemovedCallback : this delegate use when cached item is removed from cache, we can store the info to DB.
- Cache Dependency
- When the file changes, the cache will remove.
- https://www.youtube.com/watch?v=cB9TlZB3pSw#t=61.538684 (DB)
Different between Cache and Session and Application
- Cache and Application is per application(Shared all user), Session is per user.
- Cache can be remove in expire, full or dependency changes, but Session will stay until session end. Application do not time out or file dependency.
- Cache and Application is keep in process worker, Session can keep in external (state server or SQL server) and apply for Web Farm.
