When I ask for a page, I see it serialized and stored on disk (and in the 2nd level cache), after it is rendered, so in the detach phase. Also the page itself is stored in the session.
When I ask for the page again, it is found in the session. So the serialized page is not consulted.
When I ask for the page in another session, the page is created anew. I thought that in this case the serialized page would have been used.
So can you give me an example, a scenario, where the serialized page is read from disk (or 2nd level cache)?
See this url trace:
direct your browser to your app:
http://localhost:8080/
Wicket creates an instance of the homepage and redirects to:
http://localhost:8080/?0
direct your browser to your app once again:
http://localhost:8080/
Wicket creates another instance of the homepage and redirects to
http://localhost:8080/?1
now press the back button so your browser requests the first instance again:
http://localhost:8080/?0
The first page instance is now deserialized from disk.
The http session keeps a live reference only to the page which has been used in the last request cycle. Any older pages are only in the disk. If your users use the browser back button then the old instance is loaded from the disk.
A file on the disk is used to store the pages per session. I.e.different users have different files with their own pages. Sharing the files would be a security issue, it is like sharing the http sessions.
Extra info: The disk storage is part of Wicket and used as default persistent storage. WicketStuff-DataStores module provides implementations with Redis, Hazelcast, Cassandra and Memcached. They could be used in case you want the old pages to be available in a cluster of web servers.
Related
I'm trying to understand how Next JS does dynamic routing and I'm a little confused on how to properly implement it in my own website. Basically, I have a database (MySQL) of content that keeps growing, let's say they're blog posts, with images stored in GCS. From what I understand you can create a pages/[id].js file in your pages folder that can handle dynamically creating routes for new pages, but, in order for you to get a good SEO score you, the Google crawlers need to see your content before any javascript or data requests are made. So the pages have to be physically available for the content to instantly appear upon loading. So if I have pages/[id].js and I have content added to the database daily, how are physical content files supposed to spontaneously populate the pages folder? And if pages files keep getting created, how do I prevent my disk from running out of space? I'm sure there is something I'm not understanding.
I read on nextjs.org that you can have a function getStaticPaths that needs to return a list of possible values for 'id'. I'm wondering, if my site is live and new content (pages) is constantly being added to the database with their own unique ids, how is it "aware" of those ids? Do I need to write a program or message queue system that constantly appends new ids to a file that is read by getStaticPaths? What if I have to duplicate my site on multiple servers around the world, or if a server dies, do I have to keep track of the file's contents in order to boot up a new server with the same content?
From what I understand, in order for Google to see any sort of content on your website, the pages text (content) needs to be static and quickly available via physical files. Images and everything else can be loaded later since Google's crawlers mainly care about text. So if every post needs to be a physical file in your app's pages folder, how do new pages files get created if the content is added to the database?
TL:DR My main concern is having my content readily available for Google crawlers in order to get a good score for my website. How do I achieve that if content is added to my database?
As you stated before, you can set up getStaticPaths to provide a list of values for id at build time. If I understand correctly, you are most concerned about what happens to new content added after the initial build.
For this you have to return the fallback key from getStaticPaths.
If the fallback key is false, then all IDs not specified initially will go to 404 and you’d need to rebuild the app every time you add new content. This is what you don't want.
If you set it to true, then the initial values will be prerendered just like before, but new values will NOT go 404. Instead, the first user visiting a path with a new Id will trigger the rendering of that new page. This allows you to dynamically check for new content if a request hits an id that wasn't available at build time.
It is interesting here that the first visitor will temporarily see a ‘fallback’-version of the page, while next.js processes the request. On that fallback, you would usually just show a loading spinner. The server then passes the data to the client in order to properly render the full page. So in practice, the user will first see a loading indicator, then the page updates itself with the actual content. Subsequent visitors will get the now prerendered result immediately.
You may now be worried about crawlers hitting that fallback page and not getting SEO content. This concern has been addressed here: https://github.com/vercel/next.js/discussions/12482
Apart from being able to serve new pages after build, the fallback strategy has another use in that it allows you to prerender only a small subset of your website (like your most visited pages), while the other pages will be generated only when necessary.
From the docs: When is fallback: true useful?
You may statically generate a small subset of pages and use fallback:
true for the rest. When someone requests a page that’s not generated
yet, the user will see the page with a loading indicator. Shortly
after, getStaticProps finishes and the page will be rendered with the
requested data. From now on, everyone who requests the same page will
get the statically pre-rendered page.
This ensures that users always have a fast experience while preserving
fast builds and the benefits of Static Generation.
I am working on linkchecker and want to know that when AEM saves the URLs in /var/linkchecker and on what basis?
If i am opening a link,then it saves it,or it has a polling like it traverse the complete content and put it in /var/linkchecker.
Which java class help to store valid or invalid links in its storage directory?
LinkChecker is based on an eventHandler for /content (and child) nodes on creates and updates. All content is parsed and links are validated against allowed protocols and (configurable) external site links.
External Links
All the validation is done asynchronously in the background and the HTML is updated based on verification results.
/var/linkchecker is the cache for external links. The results based on simple GET requests to external links in order to optimise the process. The HTTP 200/30x response means that the links are valid. AEM looks at this cache before requesting a validation of the external link in order to optimize the page processing. This also means that the link validation is NOT real time and the delay is proportional to the load on your server.
All the links that have been checked can be seen via the /etc/linkchecker.html screen where you can request for revalidation and refresh the status of the links.
You can configure the frequency of this background check via the Day CQ Link Checker Service configuration under /system/console/configMgr. The default interval is 5 seconds (scheduler.period parameter).
Under the config manager /system/console/configMgr you will find a lot of other Day CQ Link * configurations that control this feature.
For example, Day CQ Link Checker Transformer contains config for all the elements that need to be transformed by the link checker.
Similarly Day CQ Link Checker Info Storage Service configures the link cache.
Internal Links
Internal links are ignored unless they used FQDN and external urls (which is not normally the case on author). The only exception is in a multi-tenant environment where page from one site links to another site and all the mapping information is stored in sling mappings.
Wicket offeres these concepts for pages and page links (afaik):
Bookmarkable Links do not depend on any session information. The URL may not contain session ids, version numbers, etc.
Stateful Pages are stored on the server so they can be used later in the session (e.g. for AJAX communication or for the browser's back function). Stateless pages are always created freshly for each request.
Page Versioning creates one version of a page instance per request and stores it in the session. Each version has a session unique id that is used in the page links to address a specific version directly. The url looks like that (the '8' indicated the 8th version of the profile page within this session): http://.../wicket7/profile?8
The Wicket documentation mentions these dependencies:
Stateless pages have always bookmarkable links (makes sense...)
Non-bookmarkable links point always to stateful pages (ok, the logical inverse...)
Stateful pages may have both, bookmarkable and non-bookmarkable links
It seems that stateful pages are always versioned. But I believe that there are situation where you want your pages stored, but not versioned. Furthermoree it seems to me that versioned pages have no bookmarkable link since the version id relies on the session. So this is my questions:
Are stateful pages always versioned? Is there a good practice to switch off versioning but keep storing stateful pages?
Frank,
If you don't want to have "version" in url I recommend to add following code to your Application.init
getRequestCycleSettings().setRenderStrategy(RenderStrategy.ONE_PASS_RENDER);
Look into RenderStrategy for more information.
I'm looking to move an existing website to Google Cloud Storage. However, that existing website has changed its URL structure a few times in the past. These changes are currently handled by Apache: for example, the URL /days/000233.html redirects to /days/new-post-name and /days/new-post-name redirects to /days/2002/01/01/new-post-name. Similarly, /index.rss redirects to /feed.xml, and so on.
Is there a way of marking an object in GCS so that it acts as a "symlink" to another GCS object in the same bucket? That is, when I add website configuration to a bucket, requesting an object (ideally) generates a 301 redirect header to a different object, or (less ideally) serves the content of the other object as its own?
I don't want to simply duplicate the object at each URL, because that would triple my storage space. I also can't use meta refresh headers inside the object content, because some of the redirected objects are not HTML documents (they are images, or RSS feeds). For similar reasons, I can't handle this inside the NotFound 404.html with JavaScript.
Unfortunately, symlink functionality is currently not supported by Google Cloud Storage. It's a good idea though and worth considering as a future feature.
In my web application, I am using Cookie Based session, and thus that session is being shared among all browser tabs, Is there a way to restrict user to have access of application in one tab at a time with the use of tokens(Token Interceptor)? Opening up in a new tab will invalidate the previous tab pages (i.e all application jsp pages including login page)
In short this is not possible and only solution which come to my mind is force user to use a single instance of your application by writing URLs on the fly use a sessionID.
I am not sure why you need this and what exactly is your use case.If i am correct there is such feature in spring security which help us to keep only one instance per logged in user and all you need to set a property in your spring-security xml file like
<session-management>
<concurrency-control max-sessions="1" />
</session-management>
For details refer to these threads
how-to-differ-sessions-in-browser-tabs
allow-only-one-session-per-user