Okay, so I have an old ASP Classic website. I've determined I can reduce a huge number of DB calls by caching the data daily. Our site data is read only, and changes very slowly. I think based on our site usage, I would be able to cache pages by query string for every visit each day, without a hit to our server.
My first thought was to use Output Caching, but the problem I discovered right away was that it wasn't until the third page request was generated that I gained any performance. I verified this using SQL profiler, but I'm not sure why.
My second thought was to add this ObjPageCache include file from https://web.archive.org/web/20211020131054/https://www.4guysfromrolla.com/webtech/032002-1.shtml After some research I discovered that this could cause more issues than it may solve http://support.microsoft.com/kb/316451
I'm hoping someone on here will tell me that since 2002 the issue with Sending ServerXMLHTTP or WinHTTP Requests to the Same Server has been resolved with Microsoft.
Depending on how your data is maintained you could choose from a number of ways to cache it.
If your data is changed and saved in one single place you could choose to generate an html-file which you save to the serverdisk and refer to in your linking. This will require write access for the process running your site though (e.g. NETWORK SERVICE). This will produce fast pages as the server serves these pages without any scriptingengine getting involved.
Another option is reading the data into an DomDocument which you store in the Application object and refer to on the page that needs it (hence saving the roundtrip to the database). You could keep two timestamps together with the cached data (one for the cachingtime and one for the time of change of data in the database). Timestamps will allow for fast check for staleness of the cached data: cached timestamp <> database timestamp => refresh data; otherwise use cached data. One thing to note about this approach is that Application does not accept objects other than multithreaded object so you will have to use the MSXML2.FreeThreadedDomDocument.6.0
Personally I prefer the last one as it allows for a more dynamic usage and I don't have to worry about write access permissions for the process running my site (which would probably pose security risks anyways).
Related
Correct me if I'm wrong, but from my understanding, "database caches" are usually implemented with an in-memory database that is local to the web server (same machine as the web server). Also, these "database caches" store the actual results of queries. I have also read up on the multiple caching strategies like - Cache Aside, Read Through, Write Through, Write Behind, Write Around.
For some context, the Write Through strategy looks like this:
and the Cache Aside strategy looks like this:
I believe that the "Application" refers to a backend server with a REST API.
My first question is, in the Write Through strategy (application writes to cache, cache then writes to database), how does this work? From my understanding, the most commonly used database caches are Redis or Memcached - which are just key-value stores. Suppose you have a relational database as the main database, how are these key-value stores going to write back to the relational database? Do these strategies only apply if your main database is also a key-value store?
In a Write Through (or Read Through) strategy, the cache sits in between the application and the database. How does that even work? How do you get the cache to talk to the database server? From my understanding, the web server (the application) is always the one facilitating the communication between the cache and the main database - which is basically a Cache Aside strategy. Unless Redis has some kind of functionality that allows it to talk to another database, I don't quite understand how this works.
Isn't it possible to mix and match caching strategies? From how I see it, Cache Aside and Read Through are caching strategies for application reads (user wants to read data), while Write Through and Write Behind are caching strategies for application writes (user wants to write data). Couldn't you have a strategy that uses both Cache Aside and Write Through? Why do most articles always seem to portray them as independent strategies?
What happens if you have a cluster of webs servers? Do they each have their own local in-memory database that acts as a cache?
Could you implement a cache using a normal (not in-memory) database? I suppose this would still be somewhat useful since you do not need to make an additional network hop to the database server (since the cache lives on the same machine as the web server)?
Introduction & clarification
I guess you have one misunderstood point, that the cache is NOT expclicitely stored on the same server as the werbserver. Sometimes, not even the database is sperated on it's own server from the webserver. If you think of APIs, like HTTP REST APIs, you can use caching to not spend too many resources on database connections & queries. Generally, you want to use as few database connections & queries as possible. Now imagine the following setting:
You have a werbserver who serves your application and a REST API, which is used by the webserver to work with some resources. Those resources come from a database (lets say a relational database) which is also stored on the same server. Now there is one endpoint which serves e.g. a list of posts (like blog-posts). Every user can fetch all posts (to make it simple in this example). Now we have a case where one can say that this API request could be cached, to not let all users always trigger the database, just to query the same resources (via the REST API) over and over again. Here comes caching. Redis is one of many tools which can be used for caching. Since redis is a simple in-memory key-value storage, you can just put all of your posts (remember the REST API) after the first DB-query, into the cache. All future requests for the posts-list would first check whether the posts are alreay cached or not. If they are, the API will return the cache-content for this specific request.
This is one simple example to show off, what caching can be used for.
Answers on your question
My first question is, why would you ever write to a cache?
To reduce the amount of database connections and queries.
how is writing to these key-value stores going to help with updating the relational database?
It does not help you with updating, but instead it helps you with spending less resources. It also helps you in terms of "temporary backing up" some data - but that only as a very little side effect. For this, out there are more attractive solutions (Since redis is also not persistent by default. But it supports persistence.)
Do these cache writing strategies only apply if your main database is also a key-value store?
No, it is not important which database you use. Whether it's a NoSQL or SQL DB. It strongly depends on what you want to cache and how the database and it's tables are set up. Do you have frequent changes in your recources? Do resources get updated manually or only on user-initiated actions? Those are questions, leading you to the right caching implementation.
Isn't it possible to mix and match caching strategies?
I am not an expert at caching strategies, but let me try:
I guess it is possible but it also, highly depends on what you are doing in your DB and what kind of application you have. I guess if you find out what kind of application you are building up, then you will know, what strategy you have to use - i guess it is also not recommended to mix those strategies up, because those strategies are coupled to your application type - in other words: It will not work out pretty well.
What happens if you have a cluster of webs servers? Do they each have their own local in-memory database that acts as a cache?
I guess that both is possible. Usually you have one database, maybe clustered or synchronized with copies, to which your webservers (e.g. REST APIs) make their requests. Then whether each of you API servers would have it's own cache, to not query the database at all (in cloud-based applications your database is also maybe on another separated server - so another "hop" in terms of networking). OR (what i also can imagine) you have another middleware between your APIs (clusterd up) and your DB (maybe also clustered up) - but i guess that no one would do that because of the network traffic. It would result in a higher response-time, what you usually want to prevent.
Could you implement a cache using a normal (not in-memory) database?
Yes you could, but it would be way slower. A machine can access in-memory data faster then building up another (local) connection to a database and query your cached entries. Also, because your database has to write the entries into files on your machine, to persist the data.
Conclusion
All in all, it is all about being fast in terms of response times and to prevent much network traffic. I hope that i could help you out a little bit.
I have an application build in ColdFusion MVC framework "Mach-II" and hosted on blue dragon ColdFusion server.
It causes caching issue. When i added a new page with some contents and load the page than it's working fine. But when i made some changes in the same file and hit it again its not update my changes. Its always showing me the content that i have made in the very first time. Its seems like that the server is caching my page and did not consider further changes. I have tried many solutions but failed to solve the problem.
Please let me know if you have any solution for that.
This is a bit too long for a comment - but it's not much of an answer.
First off, your question is quite broad for StackOverflow. If you aren't looking at the code yourself, and have nothing to show us, there is no guarantee we can help you at all.
It sounds like maybe this service is using query caching - which looks something like this.
<cfquery datasource="CRM" name="testQuery" cachedwithin="#CreateTimeSpan(0,0,30,0)#">
-SQL logic-
</cfquery>
Basically it stores a query's result in memory on the server. It can really help reduce strain on the database. It's possible that they've set a time limit on this caching feature that's longer than you'd like.
If you don't have access to the code, THIS is the issue you want to ask about first.
Edit: It may be entirely different.
https://docs.oracle.com/cd/E13176_01/bluedragon/621/BlueDragon_621_WL_User_Guide.html#_Toc121303111
From source:
Where ColdFusion (5 and MX) defines a ‘template cache” as a place to
holds templates in memory once rendered from source code, BlueDragon
has the same notion but refers to this as the “file cache”. In both
engines, a template once rendered from source will remain in the cache
until the server (or J2EE or .NET web app) is restarted.
The cache size, specified in the Admin Console, indicates how many of
these cached templates to keep. It defaults to 60 but that number may
need to change for your application, depending on how many CFML
templates your application uses. One entry is used for each template
(CFM or CFC file) requested.
It’s very important to understand that this is not caching the OUTPUT
of the page but rather the rendering of the template from source into
its internal objects. One cached instance of the template is shared
among all users in the application.
As in ColdFusion, once the file cache is full (for instance, you set
it to 60 and 60 templates have been requested), then the next request
for a template not yet cached will force the engine to flush the
oldest (least recently used) entry in the cache to make room.
Naturally, if you set this file cache size too low, thrashing in the
cache could occur as room is made for files only to soon have the
flushed file requested again.
It sounds like you might have to either restart the ColdFusion application or clear the Template Cache in the CFAdmin.
I store data in
HttpContext.Current.Application.Add(appKey, value);
And read data by this one:
HttpContext.Current.Application[appKey];
This has the advantage for me that is using a key for a value but after a short time (about 20 minutes) it does not work, and I can not find [appKey],because the application life cycle in iis data will lose.
i want to know is that another way to store my data by key and value?
i do not want sql server,file,... and want storing data on server not on client
i store users some data in it.
thanks for your helping
Since IIS may recycle and throw away any cache/memory contents at any time, the only way you will get data persisted is to store it outside IIS. Some examples are; (and yes, I included the ones you stated you didn't want just to have the list a bit more complete, feel free to skip them)
A SQL database (there are quite a few free ones if the price is prohibitive)
A NoSQL database (same thing there, quite a few free ones and usually simpler to use for key/value)
File (which you also stated you didn't want)
Some kind of external memory cache, a'la AppFabric cache or memcached.
Cookies (somewhat limited in size and not secure in any way by default)
you could create a persistent cookie on the user's machine so that the session doesn't expire, or increase the session timeout to a value that would work better for your situation/users
How to create persistent cookies in asp.net?
Session timeout in ASP.NET
You're talking about persisting data beyond the scope of a session. So you're going to have to use some form of persistent storage (Database, File, Caching Server).
Have you considered using AppFabric. It's actually pretty easy to implement. You could either access it directly from your code using the nuget packages, or you could just configured it as a session store. (I think) doing the latter would mean you'd get rid of the session timeout issue.
Do you understand that whatever you decide to store in Application, will be available for all users in your application?
Now regarding your actual question, what kind of data do you plan on storing? If its user sensitive data, then it probably makes sense to store it in the session. If it's client specific and it doesn't contain any sensitive information, than cookies is probably a reasonable way forward.
If it is indeed an application wide data and it must be the same for every user of your application, then you can make configuration changes to make sure that it doesn't expiry after 20 minutes.
What's the difference b/w web content cache and application cache.
On my system Firefox is using a space of 400MB for web content cache.
Application cache refers to the mechanism by which a Web application can store data on the server side. The actual store varies, it can be a database, in-memory, etc. This is usually done for performance reasons. For example, a call to get data from a database may take considerable amount of time and may not change often. Once the data is fetched initially, the developer may chose to put it in App Cache to get it quickly from memory next time as opposed to call the DB again.
Browser-cache refers to the data stored on the user's computer (client). Browsers, for example, may cache images, style sheets, etc. This depends on how the server responds to the browser requests. For example, a server may send certain headers in the response indicating that a javascript file should be cached until changed on the server, etc. This way, Browsers improve the user experience by not re-downloading data unnecessarily multiple times.
I have developed application using ZF.The app is little big with a lots of features.
I use Zend_Application(already using autoloader in constructor),Zend_Layout,Zend_view,Zend_form,etc. My current issue is, the page loading is very slow and that too in localhost with XAMP.
I have enabled xdebug, to investigate the issue, got a cachegrind file in "tmp" folder and tried to view it with WinCachegrind software. There i can a see a lot of processes and functions being run for each and every request or page load.
Also, i have installed YSlow add-on for firefox and observed the speed of page loads in seconds...I have compare the speed with ZF and non ZF applications. And from the comparison, the pages for non zf app takes less than 1 sec to load and for the ZF app, it takes atleast 6-7 seconds. What a huge difference.
Main Things happen in the app are :
1) Database connection happens for each request.
2) Im not adding the view to layout explicitly,ZF just appends it automatically, to layout.phtml, based on the action name.
3) Some windows have forms with few drop down boxes which fetches data from the database.
4) Have menus with ACL implimented, before it was loading the privilges from DB for each and every request, but now i have optimized it, so that it will work only duiring the login and rest of the time it will take from the Zend_Registry.
I would like to attach the cachegrind file so that some one can see whats happening in the background, but i cant see an option here for attaching.
Someone please help me to find a solution for this. Any kind of help is really appreciated. Thanks a lot
Let's try to give some hints.
First database connection should happen only once (except if you use several privileges access on the database or several databases). So check that you use Singleton patterns with you Zend_Db_Tables object
Then you do not use Zend_Cache. You should really start to use Zend_Cache and build several cache objects. Let's say for example a File cach, with long term storage, and a memcache or Apc Cache, storing objects. Then use these cache in several layers:
gives the FileCache to Zend_Db_Table (defaultMetaDataCache), this way you will avoid a loot of metadata queries, queries that ask for description of each columns of the tables you use.
Store one or more Acl object (depends on how you use Acl, if you have one big Acl with all rules or several with subsets). And store them in mid-duration caches when they are built.
Think of other usages, detect heavy loops, semi-static contents (like you select lists, how many time should they be considered static?)
Finally, get a whole mental image of how your application engine works, and how your data will grow and be used.You will need that step to use application levels caches in the very best way (for example should some elements be cached for groups of users?, should Acl objects be build for groups, for each user, for everybody, is ther some blocks in the layout that should be rendered the same for everybody?).