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WordPress Caching Comparisons Part 2

This post has been on my mind for quite some time now, ever since I wrote Part 1 over 1 year ago.

Part 1 only really addressed opcode 1 and Object caching 2 and didn’t really touch page caching 3. In this post I have revisited all tests and added in comparisons of using both the APC Object Cache + Batcache plugins as well as using the W3 Total Cache plugin.

Tests

  • No opcode, no caching
  • APC opcode, no caching
  • APC opcode, APC object caching plugin
  • APC opcode, W3 Total Cache APC object caching
  • APC opcode, APC object caching plugin, Batcache page caching
  • APC opcode, W3 Total Cache APC object and page caching

Comparison Stats

  • PHP generation time 4
  • Number of include/include_once/require/require_once calls 5
  • Number of stat() calls per dtruss/strace 6
  • cURL time to start transfer 7
  • Apache Bench (ab) tests for concurrency 8 and requests per second

For the above stats gathering, with PHP generation time and cURL time to start transfer, 102 sets were collected, the first 2 were dropped due to cache priming, the remaining 100 were used, and averaged. With the Apache Bench tests, 12 sets were used, dropping the highest and lowest value, and averaging across the remaining 10. Include and stat() counts were gathered over 5 sets not requiring averaging as they were the same between runs.

To find the optimal concurrency and req/s for Apache Bench, I performed manual testing, visually inspecting the results until I reached what I classified as a “sweet spot”. Using the “sweet spot” stats, I performed additional sets to gather the averages for requests per second.

The Setup

  • 256MB Rackspace Cloud Server
  • Ubuntu 11.04 amd64
  • Apache 2.2.17 - Default Ubuntu Install, no modifications, default document root located at /var/www
  • PHP 5.3.5 (mod_php) - Default Ubuntu Install, no modifications
  • PHP APC 3.1.3p1 - Default Ubuntu Install, no modifications
  • MySQL 5.1.54 - Default Ubuntu Install, no modifications
  • WordPress 3.3-beta4-r19470 - Default Install, requests made to the “home” page
  • APC Object Cache trunk version
  • Batcache trunk version
  • W3 Total Cache 0.9.2.4

I have not compared static file caching yet and hope to compare W3 Total Cache and WP Super Cache in the future. In this comparison I am mainly focusing on opcode, object caching and page caching.

I am going to try to keep this comparison about the stats only, and not make this a critique or review of the plugin, although in some cases this will not be possible.

Test Data

No opcode and no caching:
PHP Generation Time: 0.13787 seconds
Number of includes: 80
Number of stat calls: 266
cURL time to start transfer: 0.15463 seconds
Apache Bench Concurrency: 15
Apache Bench Requests Per Second: 19.1483 req/s

APC opcode and no caching:
PHP Generation Time: 0.05088 seconds
Number of includes: 80
Number of stat calls: 148
cURL time to start transfer: 0.05673 seconds
Apache Bench Concurrency: 60
Apache Bench Requests Per Second: 68.2636 req/s

APC opcode and APC Object caching:
PHP Generation Time: 0.03407 seconds
Number of includes: 81
Number of stat calls: 148
cURL time to start transfer: 0.03975 seconds
Apache Bench Concurrency: 260
Apache Bench Requests Per Second: 77.7214 req/s

APC opcode and W3TC APC Object caching:
PHP Generation Time: 0.03993 seconds
Number of includes: 102
Number of stat calls: 285
cURL time to start transfer: 0.04591 seconds
Apache Bench Concurrency: 200
Apache Bench Requests Per Second: 67.581 req/s

APC opcode and APC Object and Page caching with Batcache:
PHP Generation Time: N/A
Number of includes: Unable to collect
Number of stat calls: 41
cURL time to start transfer: 0.00316 seconds
Apache Bench Concurrency: 600
Apache Bench Requests Per Second: 147.2156 req/s

APC opcode and W3TC APC Object and Page caching:
PHP Generation Time: N/A
Number of includes: Unable to collect
Number of stat calls: 87
cURL time to start transfer: 0.00625 seconds
Apache Bench Concurrency: 500
Apache Bench Requests Per Second: 147.8425 req/s

Conclusions

I can state the following about just enabling APC in PHP, if you do nothing else, you should at least do this:

  1. 170% PHP generation time improvement by enabling APC opcode caching
  2. 172% Time to start transfer improvement by enabling APC opcode caching
  3. 300% concurrency improvement by enabling APC opcode caching
  4. 256% requests per second improvement by enabling APC opcode caching

I see performance improvements using both APC+Batcache and W3 Total Cache. However, in all tests, APC+Batcache seems to outperform W3 Total Cache, in PHP generation time, number of includes, number of filesystem stat() calls, time to start transfer, number of concurrent requests and requests per second with relation to concurrency.

I was able to push APC+Batcache to 700 concurrent requests, but req/s dropped. W3TC capped out at 500 concurrent requests, and would go no further, however 500 requests per second provided the highest req/s for W3TC.

W3TC does provide a lot of additional functionality to help reduce load on the server, such as tweaking client side caching, and using a CDN, where APC+Batcache does not, although there are small unitasking plugins that can add the missing functionality for you such as:

APC+Batcache consists of adding 3 new files, and no new directories. The W3TC download consists of 60 new directories and 351 files. The directory listing level for W3TC being as deep as it is, 5 levels deep past the directory for the plugin itself, causes a significant increase in filesystem stat() commands.

Most shared hosting providers as well as many multiserver environments will often host their web roots on NFS, and the more filesystem stat() calls, the worse performance you will see, especially under higher load.

Something else to note, is a lot can be done on the server to also improve performance. You can also use caching applications that logically sit in front of the webserver to cache, instead of using caching plugins, which will also improve performance. There are probably eleventy billion ways to improve performance, so if in doubt, consult an expert to help.

Notes:

  1. opcode: A technique of optimizing the PHP code and caching the bytecode compiled version of the code, to reduce the compilation time incurred during PHP code execution #
  2. Object Caching: An in memory key-value storage for arbitrary data, to reduce processing, and storage of external calls to speed up retrieval and display of information #
  3. Page Caching: Full caching of HTML output for web pages #
  4. PHP generation time: The amount of time taken to compile and execute the PHP code into the resulting HTML #
  5. Include/Require Count: The number of calls to the PHP include, include_once, require and require_once functions, which are used to load a separate file #
  6. stat() call count: The number of unix system calls that return information about files, directories and other filesystem related objects. #
  7. Start Transfer Time: The amount of time between the request from the client to the server, and when the server begins returning data to the client #
  8. Concurrency: The number of concurrent client requests to the server #
Code CoolStuff HowTo PHP Technology Uncategorized WordPress

WordPress Caching Comparisons Part 1

For some time now I have been wanting to write an up to date XCache object cache plugin for WordPress. Around 4 years ago I did an opcode caching comparison between APC, XCache and eAccelerator. My results had shown that at the time that XCache was the fastest of the 3. Unfortunately I didn’t think to keep that data around. As a result of these tests I had standardized the environment I was working on with XCache, and have never thought twice about it. Since I use XCache for opcode caching everywhere, it seemed like writing such an object cache plugin would be beneficial. After writing the plugin I figured it best to test performance, comparing it to the Memcached object cache and the APC Object cache. I tweeted a lot during my initial testing, and got an overwhelming response to write up a post, and here we are…

I’ll try to make this comparison comprehensive, but it can be a little difficult to always cover everything.

The test environment:

  • Toshiba T135-S1310
  • Intel SU4100 64bit Dual-Core 1.3GHz
  • 4GB DDR3 Memory
  • Ubuntu 10.10 64bit
  • Apache 2.2.16
  • PHP 5.3.3
  • PHP XCache 1.3.0
  • PHP APC 3.1.3p1
  • Memcached 1.4.5
  • Pecl Memcached 3.0.4
  • MySQL 5.1.49 No caching configured
  • cURL 7.21.0
  • WordPress 3.1-alpha (r16527) Default install with Twenty Ten and no plugins other than the one I mention below

The times are based off of the standard timer_stop() code often found in the footer.php of themes, in this case added using the wp_footer filter through a mu (must use) plugin:

<?php
add_action('wp_footer', 'print_queries', 1000);
function print_queries() {
?>


<!-- <?php echo get_num_queries(); ?> queries. <?php timer_stop(1); ?> seconds. -->


<?php
}

cURL was used to make the HTTP requests and grab the value from the comment created by the above code:

for (( c=1; c<=101; c++ )); do curl -s http://wordpress.trunk/ | grep '</body>' -B 1 | head -1 | awk -F"queries. " '{print $2}' | awk -F" seconds" '{print $1}'; done;

In each data set I gather 101 results and omit result 1 so that we only have results after the initial cache is generated. The tests are only performed on the home page.

The tests:

  1. No Object or Opcode Cache
  2. Memcached Object Cache with no Opcode Cache
  3. Memcached Object Cache with APC Opcode Cache
  4. Memcached Object Cache with XCache Opcode Cache
  5. APC Object and Opcode Cache
  6. APC Opcode Cache with no Object Cache
  7. XCache Object and Opcode Cache
  8. XCache Opcode Cache with no Object Cache

I didn’t evaluate eAccelerator due to the fact that it isn’t available in the Ubuntu repositories and I did not feel likely compiling…

The results (in seconds):

For a larger view of the spreadsheet above or if you cannot see it, take a look here.

These results are quite interesting and actually shocked me a little bit. The first thing that I found when developing an up to date XCache Object Cache plugin was that it can’t handle objects! So the plugin has to serialize all data when setting, and unserialize when retrieving. This of course is going to add overhead to every operation.

When I first tested the Memcached Object Cache I was surprised at how little it improved speed. It took me about an hour to realize that the comparison of just using Memcached was unfair as it didn’t include any Opcode caching, adding an Opcode cache brings it more in line with what I would expect.

Using an opcode cache improves performance by over 200% on a stock WordPress install without using any object caching. While APC and XCache provided similar results, my tests still show XCache to be ever so slightly faster as an opcode cache.

Where we see the biggest difference between the 3 of these caches when using APC for both opcode and object caching.

Assuming we are using both Opcode and Object caching here are the results from best to worst:

  1. APC
  2. Memcached (With either APC or XCache)
  3. XCache

At this point the single largest failure of XCache is it’s inability to store objects, so I am pretty much planning on dropping XCache on my servers in favor of APC, which will be included with PHP as of PHP 6. I would likely still see marginal speed improvements using XCache on sites that I am not using XCache for an object cache, but on those that I am I’ll get much improved performance off of APC or Memcached.

Now why would I want to use APC over Memcached or vice versa? Well, the one thing that Memcached provides that APC doesn’t is the ability to share the cache between servers. In a load balanced multi web server environment, using APC you would be duplicating the cache on all of the servers as APC provides no way to share this data or allow for remote connections. Memcached however, being a PHP independent daemon can be used for pooling resources and allowing remote connections. You also can get more bang for your buck with Memcached in a load balanced multi server environment because of it’s pooling capability. The pooling capability allows you to dedicate say 128MB of RAM to each memcached instance and when pooled together will give you 128MB x N where N is the number of servers in the pool. Anyway, I digress…

In the end, if you have WordPress hosted on a single web server, APC is the way to go. If you are in a multi web server environment, Memcached is the way to go, but remember to install an Opcode cache as well. If you are crazy and just want to use more CPU cycles, XCache is the way to go.

Some of you may be thinking “why would I need an object cache in addition opcode caching, if the results are similar?” Well, under higher load an object cache will respond better than MySQL, even with MySQL caching. In addition, other factors with MySQL can come into play, such as connectivity to the MySQL server. It may be on another server, with not enough memory, slow disks, with an overloaded network, which decreases performance. Any time that an update query is run, MySQL will flush the whole cache. Another benefit, is we are rarely, if ever, going to use the data exactly as it is given to us from the MySQL query. In the end we are going to process the data before displaying, an object cache allows you to store the processed data, rather than the raw data from the query saving CPU cycles required for the processing. Individually these items may not consume much time, but added together and in a more efficient delivery system, this can make a huge difference.

Now for any of you who go run out and install Memcached, if you install version 1.4.x make sure you get at least pecl memcached 2.2.6 or 3.0.4. Memcached made a change that breaks deletes with earlier pecl memcached versions, which adversely affects WordPress.

A few additional things that I have been asked to talk about are using caching with a WordPress Network, output caching with Batcache and query counts. I promise to get to those, but I just wanted to get this out sooner rather than later.

Yo Dawg! We heard you like caching so we put a cache in your cache, so you can optimize while you optimize…Sorry couldn’t resist.

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WordPress Metric Comparison of 2.9.2 and 3.0

Some times I like to look at metrics. Because I am bored? Probably. Without metrics how can really compare things. In any case I wanted to see the difference in the number of queries, generation time and peak memory usage between WordPress 2.9.2 and WordPress 3.0.

One of the things that I have heard people say since the release of WordPress 3.0 is that it is noticably faster. “Is it really?”, I asked myself. No, not out loud…or was it? Generally as much as we would like to make things faster from one release to the next, it doesn’t really happen that way. There are new features added, rewrites of code, a new default theme and in the end metrics change.

So what really changed in the way of these 3 aspects of number of queries, generation time and peak memory usage?

2.9.2:

  • 18 queries
  • 0.173 seconds
  • 15.901 MB peak memory used

3.0:

Kubrick

  • 16 queries
  • 0.209 seconds
  • 18.301 MB peak memory used

Twenty Ten

  • 15 queries
  • 0.212 seconds
  • 18.32 MB peak memory used

I have provided results as well for Twenty Ten, but so that we can perform a more apples to apples comparison we will use Kubrick. We have reduced the number of queries by 2 from 2.9.2 to 3.0, but it took 0.036 seconds longer to generate the page. In addition we now consume 2.4 MB more memory to generate the output.

I used the following code, placed at the very end of footer.php of the default theme for 2.9.2 and the very bottom of footer.php in twentyten. In 2.9.2 I removed the timer_stop line that already existed in the footer.php of the default theme.

<!--
<?php echo get_num_queries(); ?> queries
<?php timer_stop(1); ?> seconds
<?php echo round(memory_get_peak_usage() / 1024 / 1024, 3); ?> MB Peak Memory Used
-->

The testing set up:

  • Ubuntu 10.04
  • Apache 2.2.14
  • PHP 5.3.2 (Only enabled modules were mysql, gd and curl)
  • MySQL 5.1.41 (With all caching disabled)
  • Fresh installs of WordPress without any enabled plugins or modifications
  • Tests performed using curl against the front page
  • Averages over 25 tests per install

Anyway, not really the most comprehensive metrics gathering test, but just something to look at. But in the end, is WordPress 3.0 any faster? With an absolute default install, no. Does it matter that 3.0 is ever so slightly slower? No. Should I be running WordPress 3.0 now? Yes!

Hopefully you find this post useful and that I didn’t waste 15 minutes of my day that I will never get back to talk about something you could care less about.

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Using MySQL Sockets in the WordPress wp-config.php

Recently I have been getting a lot of questions about how to use a MySQL socket in place of the DB_HOST constant for WordPress in the WordPress IRC channel.

Fortunately this is pretty easy, unfortunately if you are using the web based installer you cannot specify a socket in the “Database Host” field. However, you can do things the manual way and copy wp-config-sample.php to wp-config.php and go that route.

The first thing you need to do is determine the path to the MySQL socket. By inspecting my.cnf you would need to look for something that looks like:

socket      = /var/run/mysqld/mysqld.sock

If you don’t have access to look at my.cnf you can try to run the following MySQL query:

SHOW VARIABLES LIKE 'socket';

Now crack open your wp-config.php file and set DB_HOST to ‘:/path/to/mysql.sock’. Take careful note of the ‘:’ (colon) preceding the path. In my example the define for the DB_HOST looks like:

define('DB_HOST', ':/var/run/mysqld/mysqld.sock');
CoolStuff HowTo WordPress

Detect wp_head and wp_footer from a Plugin

Normally I start these posts with “Every so often someone asks a question in the WordPress IRC channel that sparks my interest”, however today, to my great surprise someone actually caught my attention on the wp-hackers mailing list.

For those of you who didn’t click through, the question was:

Couldn’t find this on forums or anywhere else.
What can I test to check if wp_footer was placed on the theme?

Before any replies came in I was already interested and when Peter Westwood replied with “The other way to do it is to do a http request based test which a special query arg on which you output a string on wp_footer.“, I was on the hook.

I spent a few minutes writing up a test plugin, to perform only this functionality and responded back to the list. It was pretty well accepted and I got a few comments from Ozh and Andrew Nacin on Twitter. One of the comments was actually an idea, to extend the checks to make sure that the calls to <?php wp_head(); ?> and

<?php wp_footer(); ?> were in the proper places in the code.

Before I get to the code, I want to spend a little time talking about the significance of wp_head() and wp_footer(). These 2 functions are the key to functionality of a lot of plugins and are the real work horses of themes. The wp_head and wp_footer functions allow WordPress core and plugins to hook into your theme either directly before the </head> or </body> html tags in your theme and perform actions. The majority of the time these actions are used to output style sheets or JavaScript, for use by plugins. WordPress core uses it to output a lot of good functionality such as relational links to your RSS and ATOM feeds into the head of the document. Joseph Scott wrote about this nearly a year ago. His post is fairly short but does a good job at explaining why it is important to include these functions.

Back to the original discussion, which was how do we detect whether or not wp_head and wp_footer are called in the active theme, and if called are they called, was it from the proper locations?

In my proof of concept plugin, we hook into admin_init, which will actually use wp_remote_get() to retrieve the frontend of our WordPress site. It calls the url with 2 query vars, that if present will cause the plugin to hook into wp_head and wp_footer and output some content that we will later look for. If the response was successful, as in returning a 200 response code, we will look at the content to see if <!--wp_head--> and

<!--wp_footer--> are present. If they are not we will see an admin notice telling us which problems were found. If those strings were found but they were not found directly before

</head> or </body> the notice will alert you of such.

Without further adieu:

Just in case you cannot see the code above, use this link: http://paste.sivel.net/24.

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WordPress Maintenance Mode Without a Plugin Part 3

A few months ago I wrote part 1 and part 2 of WordPress Maintenance Mode Without a Plugin. Part 1 covered the basics of using the .maintenance file, and part 2 covered styling the maintenance page using wp-content/maintenance.php. Part 3 covers the short comings of the other 2 by addressing how to let a user log into the admin and allowing logged in users access to the front end of the site while in maintenance mode.

It only takes a little bit of extra code in a file called .maintenance in the root of your WordPress installation to conditionally return a time that falls within the logic described in part 1. Now without forther adieu:

<?php
function is_user_logged_in() {
$loggedin = false;
foreach ( (array) $_COOKIE as $cookie => $value ) {
        if ( stristr($cookie, 'wordpress_logged_in_') )
            $loggedin = true;
    }
    return $loggedin;
}
if ( ! stristr($_SERVER['REQUEST_URI'], '/wp-admin') && ! stristr($_SERVER['REQUEST_URI'], '/wp-login.php') && ! is_user_logged_in() )
    $upgrading = time();
?>

Just drop the above code in the .maintenance file perhaps take a look at part 2 and away you go. Enjoy!

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San Francisco WordPress Meetup

There will be a WordPress meetup held at the Automattic office at Pier 38 on August 11. I’ll be in San Francisco for the OpenSourceWorld Expo and will be attending the meetup. Numerous folks from Automattic should be there and there will be a demo of the GSoC project, currently called ‘Elastic’, which is the WYSIWYG theme designer. Mark the date on your calendars, I want to see you all there! The meetup should start around 6:30PM, feel free to show up a little early as I am sure there will be some folks there.

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WordPress Maintenance Mode Without a Plugin Part 2

A few days ago I wrote a post about WordPress Maintenance Mode Without a Plugin. A common question that I got afterwards was whether or not the maintenance page could be styled. The answer, is yes it can be.

After wp-settings.php determines whether or not to put the blog into maintenance mode it checks to see if there is a file titled maintenance.php located in WP_CONTENT_DIR which is by default wp-content/.

Simply create a file at wp-content/maintenance.php containing the code you want to display the for the maintenance page. Below is a sample of code based off of the default maintenance page.

<?php
$protocol = $_SERVER["SERVER_PROTOCOL"];
if ( 'HTTP/1.1' != $protocol && 'HTTP/1.0' != $protocol )
    $protocol = 'HTTP/1.0';
header( "$protocol 503 Service Unavailable", true, 503 );
header( 'Content-Type: text/html; charset=utf-8' );
?>

<html xmlns="http://www.w3.org/1999/xhtml">

<body>
    <h1>Briefly unavailable for scheduled maintenance. Check back in a minute.</h1>
</body>
</html>


<?php die(); ?>

Modify as needed, add some css, some images and there you go.

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Congratulations to the WordPress Community for a Successful 2.8 Release

With WordPress 2.8 having been released and amassing over 64,000 downloads in the first 12 hours, I wanted to take a few moments to give my congratulations to the WordPress team for another great release.

Many thanks go out to all of those who contributed code for the 2.8 release. I know many of you worked hard to help get this release where it is today. In total there were 153 people who contributed code to WordPress 2.8. Here is the list of people who contributed:

Aaron Campbell, Abel Cheung, adferguson, akd907, Alex Rabe, anderswc, Anton Shevchuk, arena, Askapache, Andrew Ozz, Beau Lebens, bernzilla, bkrausz, brh, brianwhite, caesarsgrunt, ceenz, CharlesClarkson, CharlieHamu, chineseleper, chmac, chrisbliss18, christmasboy81, Cimmo, clwill, Scott Reilly, danlee, dcole07, Dion Hulse, Demetris Kikizas, Denis de Bernardy, designsimply, develish, docwhat, Donncha O Caoimh, drossy, dwc, dwenaus, emartin24, empireoflight, ev3rywh3re, Federico Bond, Austin Matzko, fuggi, futurix, Lester Chan, GM_Alex, gmpfree, gortsleigh, GregMulhauser, hailin, hakre, hudatoriq, Benedict Eastaugh, Jacob Santos, jamescollins, jbsil, jcraig90210, jdub, Jeremy Clarke, Jennifer Hodgdon, John Blackbourn, johnconners, johnkolbert, JohnLamansky, Joseph Scott, Joost de Valk, jsixpack, JulienV, kambiz.k., kamiyeye, Kuba Zwolinski, Lloyd Budd, lusuonline, makibo, Malaiac, mark8barnes, markedwards, Mark Jaquith, mastermind, Matt Mullenweg, mattwalters, MattyRob, Michael Adams, mercurix, mgriepentrog, mgsisk, MichaelH, MidnighToker, minusfive, mrmist, Mr Pete, Nick Momrik , mystyman, natethelen, Nathan Rice, Nazgul, nbachiyski, neoxx, Nicholas91, nightgunner5, Noel Jackson, novalis_dt, Samuel Wood, pamelatech, Paveo, peaceablewhale, PeteHoliday, peterkz, piouPiouM, pishmishy, pne, PotterSys, projct, ranchnachos, Daniel Jalkut , richcon, ridgerunner, Ryan McCue, roganty, ruslany, Ryan Boren, Sam_a, Sam Bauers, scohoust, scribu, simek, Simon Wheatley, sirzooro, Matt Martz, srobbin, st3ff3n, stringfold, tellyworth, Charles Frees-Melvin, TimButterfield, tomontoast, topncal, Thorsten Ott, turboguy, Txanny, UnderWordPressure, Alex, Vladimir Kolesnikov, Peter Westwood, Will Norris, wnorris, yoavf, zedlander, zekrap, zeronex, zeo, znarfor

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WordPress Maintenance Mode Without a Plugin

Every so often someone asks a question in the WordPress IRC channel that sparks my interest, and in this case the core maintenance mode functionality was one of those questions. I’ve known for sometime that WordPress has it’s own maintenance mode functionality since core upgrades were added, however I had never really looked into the functionality. Hooking into this functionality is really quite simple and effective.

Start by creating a file in the root of your WordPress install (on level with wp-settings.php) called .maintenance. Note the preceding dot like a .htaccess file; in Linux this is considered a hidden file. In this file add the following code:

<?php $upgrading = time(); ?>

This code will basically cause the maintenance page to display until you remove the .maintenance file. In wp-settings.php there are 2 checks to see if it should display the maintenance page. First, it makes sure that the .maintenance file exists. Second, it checks that the current time minus the time specified by the $upgrading variable is less than 10 minutes. Using the code above will insure that it is always less than 10 minutes since time() - time() == 0. If you want it to display for a certain period of time you would want to use:

<?php $upgrading = 1234567890; ?>

For your usage you would want to replace 1234567890 with the unix formatted timestamp of the time minus 10 minutes at which you want the maintenance page to stop displaying.

For example if I wanted the maintenance page to stop displaying at November 14, 2013 at 20:13:00, I would really set the $upgrading variable to November 14, 2013 at 20:03:00. Notice the 03 instead of 13. In unix time this would look like 1384459380. And the code needed for the .maintenance file would be:

<?php $upgrading = 1384459380; ?>

Take note that if you use a specific time in the .maintenance file and you do not remove the .maintenance file, your users will see your site and not be affected, however in the admin you will see a notice stating, “An automated WordPress update has failed to complete - please attempt the update again now.” Deleting the .maintenance file will remove this notice.

I’m sure that this functionality could be wrapped in a plugin, or even better an option added to the core code in the admin. However, I am happy with just manually creating the file.

For information on modifying or styling the maintenance page see WordPress Maintenance Mode Without a Plugin Part 2.

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