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{{rejected|WP:AUM}}
<div class="messagebox cleanup" style="clear:all;">New version is due at ]</div>
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'''See ] for current discussions about the relevancy of this page.'''
] allow certain standard text to be included on many pages, usually with the idea that in the future, any changes to that text block can be changed in one place. The term "'''meta-templates'''", as used in this article, refers to nested templates which are created and used to add functions or formatting to other ''templates''.


While they can be extremely useful and convenient, it is proposed that they be avoided due to concerns that may not be immediately obvious: Meta-template schemes can be fragile and hard for new editors to understand. They may also provide an avenue for mass-vandalism and impact maintenance efforts. The reasons listed on this page argue against using meta-templates.
<div style="border: 1px solid maroon; margin-right: 80px; margin-left: 80px; padding: 12px; background-color: #fffafa">
There's a lot of talk about this 'policy' which attempts to divine meaning from things other people have said rather than just asking for details.

Complicated templates-within-templates generally ought to be thought twice about before being used, because they can be confusing and fragile. There are some good notes about that on this page; please don't go all willy-nilly with illegible code just because it sort-of works.

There are other notes on this page about server performance which are not necessarily clear or well-supported. In particular, there's no known evidence that moderate usage of meta-templates has any noticeable impact on server performance.

While there are potential issues with cache invalidation, that's a separate issue which can be separately solved -- and is little better with "regular" templates.

I'd like to ask that anyone fighting against ugly, fragile meta templates at this time '''do so based on their ugliness and fragility'''. Please don't go around claiming "the developers" laid down the law and said nobody can use meta-templates because they hurt the servers; that just isn't true.

--] 03:25, 21 January 2006 (UTC)
</div>


{| class="messagebox" id="pnutshell"
|-
|style="text-align: center"|This essay in a nutshell:
|-
|style="text-align: center"| '''Where possible avoid using templates within templates but consider carefully before replacing with other hacks (especially CSS based ones that may cause accessibility issues)'''
|}

{{shortcut|]}}

] allow certain standard text to be included on many pages, usually with the idea that in the future, any changes to that text block can be changed in one place. The term "'''meta-templates'''", as used in this article, refers to nested templates which are created and used to add functions or formatting to other ''templates''. They are extremely useful and convenient for many purposes.

However, meta-templates can also be fragile, hard to understand. they increase the number of database reads per page view affect back-end server performance; though the developers are not in agreement over whether such server impacts are significant. For these reasons, it is better to avoid meta-templates when clearer and more robust alternatives are available, such as those described below. Contrary to some perceptions, there is not a developer mandate that ''all'' meta-templates must be eliminated, but they should not be abused when more sensible alternatives are available.

In the drive to eliminate meta templates that occoured from the aforementioned perceptions of "no meta templates period" sometimes meta template based hacks were replaced with other possiblly worse hacks. An example is the "hiddenstructure" ] class which was introduced to hide empty sections of infoboxes without using the meta template based if system. Unfortunately, it only works for browsers supporting css, reducing Misplaced Pages's accessibility. Another proposed soloution was to use an extra parameter together with the optional parameters system to supress the structure but this relies on adding extra code to every page that uses the template. Ideally, hacks (whether through meta templates or otherwise) should be avoided but the slow response of the small and overworked development team makes a hack that can be implemented immediately by a normal editor or even a Misplaced Pages "admistrator" look very attractive.

Finally if there is a choice between messy unintuitive structures in articles and messy unintuitive structures in templates messy structures in templates are preferable as templates are generally maintained by experianced wikipedians whereas articles are the target of most newbie edits.

== Use of meta-templates ==
The use of metatemplates should be avoided in almost all circumstances. If you are considering using a meta-template, ask these questions.

#Is the end product ''essential'' to Misplaced Pages, or is it a primarily decorative feature? Meta-templates that are not essential should be avoided.
#Is the template likely to be high-profile? High-profile templates cause more server load, and so are less appropriate for meta-templates.
#Is the desired effect only achievable through a meta template, or can a template of basically the same appearance be made without them? If the same effect can be achieved differently, even if it is more difficult, a meta-template should be avoided.

You should not use metatemplates unless you have a really good reason that you have to.


== Harmful effects == == Harmful effects ==
The impacts of meta-templates include not only direct ] effects but also indirect effects, such as creating ] vulnerabilities.


=== Complexity === === Complexity ===
Some nested template schemes are so complex that they are prohibitively difficult for the average editor to grasp. This is particulary true in non-technical areas where the subject expert, who knows best what information should be presented in a template, is not able to edit the template due to the use of esoteric coding. As a result, routine maintenance and changes are neglected, improper usage can proliferate, and innovation suffers. The solution, meant to become an easy replacement, becomes more difficult than the function it was meant to improve. Clear article source ''and'' clear template source are most preferred, though it is understandable if complex code is moved to the template. If this is the case, steps should be taken to reduce complexity to a minimum. Nested template schemes are complex and prohibitively difficult for the average editor to grasp. This is particularly true in non-technical areas where the subject expert, who knows best what information should be presented in a template, is not able to edit the template due to the use of esoteric coding. As a result, routine maintenance and changes are neglected, improper usage can proliferate, and innovation suffers. The solution, meant to become an easy replacement, becomes more difficult than the function it was meant to improve. Clear article source ''and'' clear template source are most preferred, though it is understandable if complex code is moved to the template. If this is the case, steps should be taken to reduce complexity to a minimum.


=== Server load === === Template links ===
When a page is edited, a list of all templates in use on that page is stored in the database. This list can be seen when in edit mode as a list of links at the bottom. Not only are the templates that are directly called listed there, but any higher-level meta-templates as well. This feature was created as a helpful aid for editors, in order that they can easily tell what templates are being used on a page in case they want to edit one of them. Meta-templates clutter this list, making it unclear to editors exactly which link is correct.
The developers have noted that nested templates increase the number of back-end database calls, as each nested template is fetched and evaluated internally. As is typical of websites that use a database and cache scheme, extra database processing is more "costly" in terms of resource availability than the page caching mechanism. How much more costly meta-templates are than templates, and whether this has a noticable impact on server load, is (as of early 2006) a matter of debate. Also, when a nested template is edited, that change results in the cached version of every page using that template, whether directly or indirectly, to be marked invalidated. Pages using nested templates must be rebuilt, bringing a lot of activity onto the database servers. In some cases, editing meta-templates has caused enough server stress to temporarily lock the database.

Template links created by meta-templates also frequently cause problems for template namespace maintenance. If a Template:A is in use on several pages, but then is changed to either add or remove Template:B, any article-level template links to "B" are not updated until each article is edited or "touched". Since the links can't be fully trusted, template maintenance work which relies on that information is made difficult or impossible. ] rely on those links as well, such as when performing ] or migrating from one template to another.


=== Vandalism === === Vandalism ===
As with any template which is used on a very high percentage of pages, a nested template is an excellent ] vector, since changing it or any component used in it would flush a substantial percentage of the site caches, which are critical to site performance and normally serve some 75–80% of all hits. Making even one subtle change, like the addition of a space, causes the effect. This has led administrators to protect some of the ]. Sometimes, though, a sub-sub-sub-template could be vandalised with offensive content. These could be difficult to notice immediately, because the sub-template is not edited often and appears on only one or a few Watchlists, and difficult to track down in a timely manner. Any template which is used on a very high percentage of pages is an excellent ] vector, since changing it or any component used in it would flush a substantial percentage of the site caches, which are critical to site performance and normally serve some 75–80% of all hits. Making even one subtle change, like the addition of a space, causes the effect.


Thus, caution is warranted for those nested templates which are widely used indirectly. A sub-sub-sub-template could be vandalised with offensive content. These could be difficult to notice immediately, because the sub-template is not edited often and appears on only one or a few Watchlists, and difficult to track down in a timely manner.
== How a page is built and cached ==


It should remembered, however, that it is possible and useful to write a meta-template which will only be used on a few or even a few hundred pages. Conversely, there are templates, such as cross-reference templates, which are very widely used without being meta-templates.
''Here's some technical background which may be of use. ] 07:52, 13 Feb 2005 (UTC)'' and clarified by ] 00:22, 11 November 2005 (UTC) (Clarifications show in 's).


== Protection ==
Because of vandalism and the potential server load problems described above, several ] have had to be ], so that they can only be edited by administrators. If the meta-template is rarely changed, then any daughter templates probably don't change either, so it may make sense to move the formatting into the daughter templates. This was done with ], which now no longer use a meta-template scheme. Remember also: ].


== Conditionals ==
[Re: Rendering impact:
Schemes using layers of nested templates to mimic conditional expressions — to selectively hide or show text or images based on the ] which have been set - are sometimes created by users who are unfamiliar with the better alternatives. Conditionals should generally be avoided, unless there is a significant advantage in their use. If they must be used, then the following methods for conditional logic are available and highly preferred over using nested templates:
The first time a page is viewed, i.e. after it has been removed from caches, the page request causes several steps:]
*Each item in the base page portion is requested from the database (images and CSS aren't in the main part). The page you edit, each template, each template included in the template and so on. Two templates, two database records to be retrieved. One template on its own, one read, one template including another, two. Plus the one for the base page.
*Once that and the rest of what is called the parsing is done, the page is saved in the parser cache. That's kept in RAM in memcached.
*Finally the skin is applied and the page is passed on to the Squids, which cache it in RAM and on disk (to get larger capacity but at slower access time) for all who aren't logged in (will only be useful if it's the normal skin) and send it on to the person who originally requested it.


* ] -- This method is very common and designed to display default alternative text only if a particular parameter is -not- set. Very simple, but not very powerful for complex needs.
* ] -- Provides a framework for conditional statements within templates. Since it is built into the MediaWiki code, it is relatively efficient on the back-end, but can be very complex for non-technical editors.
*Whenever any part of a page is changed, be it the page itself or a template or image used in it:
** The page is marked as changed ("touched") and will be regenerated next time it is requested. Both the Squid and parser caches have it removed. Necessary so people see the correct version.
** The marking process involves a database update to every affected page, which for many pages can produce "replication lag" , with outdated information displayed to those using the page. This (the marking process) also shows up as slower response times when the lag is less than ten seconds. The effect is minimised by affecting small numbers of pages and maximised by affecting a large number, in part because the wait of up to ten seconds makes batches in the few thousand range effectively invisible except for delay in page load times. Touching about 18,000 pages currently takes a database slave with 4GB of RAM, 6 drive RAID 10 array and write caching disk controller some 90 seconds (that's from a real touch operation).
***Assuming even distribution across 18,000 pages, Each of the 8 edits would flush from cache one eighth of the pages in each edit. On the database side, lets look at that 90 second case:
***90/8 = 11.25 seconds, call it 12.
***Those who view in the first 2 seconds will wait ten seconds then see out of date information.
***Those who view in the remaining ten seconds will see delay of up to ten seconds and then completely current data.
***So, splitting it has removed most of the visible lag and visible problem.


== Alternatives ==
The Squids, because of the limitations in the way they can work, with much less work per page, are inherently the fastest way of serving the pages and just 4 machines can serve some 75% of all hits to the site. But they are restricted in what they can serve. Next step is using the parser cache via the apache web servers. That allows all of the user settings for logged in people but uses more web server CPU so it's much less efficient.
# '''Design, document, and then implement''' — To give an example in the case of ], a proposal was made to use a meta-template. In this area, it is much better to decide on a common look and format, document that standard for easy reference in case new related templates are needed, and then implement it across the few templates being used. When changes are needed, this gives one central place for discussion and revision. After there is consensus for the change, interested editors can quickly apply them. Creating a page which displays each template also helps to locate templates which don't follow the agreed upon format.
# '''Make use of CSS''' — Some meta-templates serve only to produce a specific visual format&nbsp;— such as size, position, color. If these were identified, ] classes could be added to the site's global stylesheets. The meta-templates could then be replaced with the CSS classes in relevant pages. This would accomplish the same purpose&nbsp;— maintaining uniform style across the site&nbsp;— without placing a burden on the server. This also allows the visual style to be personally customized.
# '''Use lists, not templates or ]''' — Some templates and categories are used with the goal of helping editors find articles under a specific topic area of interest. For this use, it is often more valuable to create a ], which can be annotated and prioritized. Many ] already maintain an area for reporting articles that need work. (Note that categories also heavily load the servers, for similar reasons.) See ]
# '''Use <nowiki>{{subst: }}</nowiki>''' — ] copies the template's text to any daughter templates(<em>subst</em>itution) rather than causing a ], thus eliminating the second template call. Of course, this means that when the meta-template is changed, the daughter templates won't update, and won't be tracked by the ] feature. This is a good solution for any template that doesn't change often or where the exact text need not be kept up-to-date on ''every'' page.


== Still want to use them? ==
We could switch everyone to using the apaches but that would be far less efficient and would require something like 4-5 times as many apaches and database servers as we have today, far more than the 4 machines gained by not using them as squids. And the page views would be slower, because it's an inherently slower process.
If you are considering using a meta-template, ask these questions:


# Is the end product ''useful'' to Misplaced Pages, or is it a primarily decorative feature? Even useful templates should be weighed against the problems above.
While all template use causes an extra database read and flush all pages using it, meta-templates are a special case because they use twice the number of database queries and can cause flushing of many more pages than other templates. If a meta-template is used in only a few or perhaps a few dozen templates which are fundamentally unrelated, it's debatable whether the extra equipment costs are worth it, compared to the relatively modest work involved in updating the individual templates. The replication lag issue can't so easily be addressed — that work is done by however many database servers are purchased. We're trying to reduce the effect but updates affecting many pages are inherently more problematic in this area than those affecting fewer.
# Is the template likely to be high-profile? High-profile templates cause more server load, and so are less appropriate for meta-templates.
# Is the desired effect only achievable through a meta-template, or can a template of basically the same appearance be made without them? If the same effect can be achieved differently, without significantly more trouble, a meta-template should be avoided.
# Will later editors understand how this works? On the other hand, will later editors understand the alternative method?


You should not use meta-templates without good reason. If you do create one, be open to other methods which achieve the same end, and be prepared to trade functionality in favor of avoiding the problems with meta-templates.
== Alternatives ==

# '''MediaWiki needs developers.''' Metatemplates that did not cause the server hit would be of great benefit to the project, if someone can work out how to implement them in such a fashion. ]. Code is equally needed to replace the meta-template based If hack.
#*Please read "The touching process involves a database update to every affected page". There are changes in 1.5 which will help. How much is currently not known. ] 14:55, 6 August 2005 (UTC)
# '''Design, document, and implement''' — To give an example in the case of ], a proposal was made to use a meta-template. In this area, it is much better to decide on a common look and format, document that standard for easy reference in case new related templates are needed, and then implement it across the few templates being used. When changes are needed, this gives one central place for discussion and revision. After there is consensus for the change, interested editors can quickly apply them. Creating a page which displays each template also helps to locate templates which don't follow the agreed upon format.
# '''Make use of CSS''' — Some meta-templates serve only to produce a specific visual format&nbsp;— such as size, position, color. If these were identified, ] classes could be added to the site's global stylesheets. The meta-templates could then be replaced with the CSS classes in relevant pages. This would accomplish the same purpose&nbsp;— maintaining uniform style across the site&nbsp;— without placing a burden on the server. This also allows the visual style to vary depending on the skin or ].
#*This would be very useful. I've previously discussed difficulties with using CSS, notably lack of project and page-specific CSS and the inability to use the span tag, which is part of the blocked HTML set. ] 14:55, 6 August 2005 (UTC)
#**<span style="background-color: silver; color: blue; font-weight:bold; border: solid green;">Hmm??</span> ] were in December 2004. — ] 01:47, 17 December 2005 (UTC)
# '''Use lists, not templates or ]''' — Some templates and categories are used with the goal of helping editors find articles under a specific topic area of interest. For this use, it is often more valuable to create a ], which can be annotated and prioritized. Many ] already maintain an area for reporting articles that need work. (Note that categories also heavily load the servers, for similar reasons.) See ]
# '''Use <nowiki>{{subst: }}</nowiki>''' when creating the daughter templates. This copies the text message to the daughter template (<em>subst</em>itution) rather than causing a ], thus eliminating the second template call. (See the descriptions of the use of subst: ] and ].) Of course, this means that when the meta-template is changed, the daughter templates won't update, and won't be tracked by the ] feature, which probably defeats the point of using a meta-template in the first place: If all of the daughter templates are to be updated, this would then have to be done by hand, expending a considerable amount of time, work and bandwidth. It's very unclear that this is better than just listing the templates and documenting the format in use on a project page for easy copy-and-pasting — ''see "Design, document and implement", above.''
#*You can also do this on the end user pages. Where it is unimportant that the latest version is displayed this is a useful approach. Having the very latest version of say a stub message on a page, when that status will change only if the page is edited and the message can then be updated, doesn't seem to matter very much, since the message that it is a stub is the important part. ] 14:55, 6 August 2005 (UTC)
#*Actually using subst with stub templates is a bad idea, see discussion at ] (archived ). Since changes to the stub categories can require revisiting all articles currently tagged with a particular stub. and for several other reasons, these should not be placed with subst. However subst can be and is used to generate new stub templates from the metastub template. ] ] 01:53, 17 December 2005 (UTC)
# '''Protection''' — Meta-templates that are used in many instances but rarely changed can be ], so that they can only be edited by administrators. This prevents vandalism and reduces the server load problem; if the meta-template is never changed, the daughter templates don't need to be updated. Note that this creates a permanantly protected page, which is also to be avoided.


== See also == == See also ==
* ]
* ]
* ]
* ]
* ]
* ] (see page history)


*] ]
*]
*]

]

Latest revision as of 19:16, 14 May 2020

Red crossThis is a failed proposal.
Consensus for its implementation was not established within a reasonable period of time. If you want to revive discussion, please use the talk page or initiate a thread at the village pump.		Shortcut

Template messages allow certain standard text to be included on many pages, usually with the idea that in the future, any changes to that text block can be changed in one place. The term "meta-templates", as used in this article, refers to nested templates which are created and used to add functions or formatting to other templates.

While they can be extremely useful and convenient, it is proposed that they be avoided due to concerns that may not be immediately obvious: Meta-template schemes can be fragile and hard for new editors to understand. They may also provide an avenue for mass-vandalism and impact maintenance efforts. The reasons listed on this page argue against using meta-templates.

Harmful effects

Complexity

Nested template schemes are complex and prohibitively difficult for the average editor to grasp. This is particularly true in non-technical areas where the subject expert, who knows best what information should be presented in a template, is not able to edit the template due to the use of esoteric coding. As a result, routine maintenance and changes are neglected, improper usage can proliferate, and innovation suffers. The solution, meant to become an easy replacement, becomes more difficult than the function it was meant to improve. Clear article source and clear template source are most preferred, though it is understandable if complex code is moved to the template. If this is the case, steps should be taken to reduce complexity to a minimum.

Template links

When a page is edited, a list of all templates in use on that page is stored in the database. This list can be seen when in edit mode as a list of links at the bottom. Not only are the templates that are directly called listed there, but any higher-level meta-templates as well. This feature was created as a helpful aid for editors, in order that they can easily tell what templates are being used on a page in case they want to edit one of them. Meta-templates clutter this list, making it unclear to editors exactly which link is correct.

Template links created by meta-templates also frequently cause problems for template namespace maintenance. If a Template:A is in use on several pages, but then is changed to either add or remove Template:B, any article-level template links to "B" are not updated until each article is edited or "touched". Since the links can't be fully trusted, template maintenance work which relies on that information is made difficult or impossible. Automated bots rely on those links as well, such as when performing Template substitution or migrating from one template to another.

Vandalism

Any template which is used on a very high percentage of pages is an excellent denial-of-service attack vector, since changing it or any component used in it would flush a substantial percentage of the site caches, which are critical to site performance and normally serve some 75–80% of all hits. Making even one subtle change, like the addition of a space, causes the effect.

Thus, caution is warranted for those nested templates which are widely used indirectly. A sub-sub-sub-template could be vandalised with offensive content. These could be difficult to notice immediately, because the sub-template is not edited often and appears on only one or a few Watchlists, and difficult to track down in a timely manner.

It should remembered, however, that it is possible and useful to write a meta-template which will only be used on a few or even a few hundred pages. Conversely, there are templates, such as cross-reference templates, which are very widely used without being meta-templates.

Protection

Because of vandalism and the potential server load problems described above, several high-use meta-templates have had to be protected, so that they can only be edited by administrators. If the meta-template is rarely changed, then any daughter templates probably don't change either, so it may make sense to move the formatting into the daughter templates. This was done with stub templates, which now no longer use a meta-template scheme. Remember also: meta:Protected pages considered harmful.

Conditionals

Schemes using layers of nested templates to mimic conditional expressions — to selectively hide or show text or images based on the parameters which have been set - are sometimes created by users who are unfamiliar with the better alternatives. Conditionals should generally be avoided, unless there is a significant advantage in their use. If they must be used, then the following methods for conditional logic are available and highly preferred over using nested templates:

  • Parameter default -- This method is very common and designed to display default alternative text only if a particular parameter is -not- set. Very simple, but not very powerful for complex needs.
  • m:ParserFunctions -- Provides a framework for conditional statements within templates. Since it is built into the MediaWiki code, it is relatively efficient on the back-end, but can be very complex for non-technical editors.

Alternatives

  1. Design, document, and then implement — To give an example in the case of Misplaced Pages:Sister projects, a proposal was made to use a meta-template. In this area, it is much better to decide on a common look and format, document that standard for easy reference in case new related templates are needed, and then implement it across the few templates being used. When changes are needed, this gives one central place for discussion and revision. After there is consensus for the change, interested editors can quickly apply them. Creating a page which displays each template also helps to locate templates which don't follow the agreed upon format.
  2. Make use of CSS — Some meta-templates serve only to produce a specific visual format — such as size, position, color. If these were identified, CSS classes could be added to the site's global stylesheets. The meta-templates could then be replaced with the CSS classes in relevant pages. This would accomplish the same purpose — maintaining uniform style across the site — without placing a burden on the server. This also allows the visual style to be personally customized.
  3. Use lists, not templates or categories — Some templates and categories are used with the goal of helping editors find articles under a specific topic area of interest. For this use, it is often more valuable to create a list, which can be annotated and prioritized. Many WikiProjects already maintain an area for reporting articles that need work. (Note that categories also heavily load the servers, for similar reasons.) See Misplaced Pages:Categories, lists, and series boxes
  4. Use {{subst: }} — Template substitution copies the template's text to any daughter templates(substitution) rather than causing a transclusion, thus eliminating the second template call. Of course, this means that when the meta-template is changed, the daughter templates won't update, and won't be tracked by the What links here feature. This is a good solution for any template that doesn't change often or where the exact text need not be kept up-to-date on every page.

Still want to use them?

If you are considering using a meta-template, ask these questions:

  1. Is the end product useful to Misplaced Pages, or is it a primarily decorative feature? Even useful templates should be weighed against the problems above.
  2. Is the template likely to be high-profile? High-profile templates cause more server load, and so are less appropriate for meta-templates.
  3. Is the desired effect only achievable through a meta-template, or can a template of basically the same appearance be made without them? If the same effect can be achieved differently, without significantly more trouble, a meta-template should be avoided.
  4. Will later editors understand how this works? On the other hand, will later editors understand the alternative method?

You should not use meta-templates without good reason. If you do create one, be open to other methods which achieve the same end, and be prepared to trade functionality in favor of avoiding the problems with meta-templates.

See also

Categories: