Unable to create `.git/index.lock`

Posted on April 13, 2026 by Mo Jangda

I was hitting this error quite regularly when Claude Code attempted git operations (git add / git checkout / git commit / etc.):

			
Error: Exit code 128 fatal: Unable to create '/path/to/.git/index.lock': File exists. Another git process seems to be running in this repository, e.g. an editor opened by 'git commit'. Please make sure all processes are terminated then try again. If it still fails, a git process may have crashed in this repository earlier: remove the file manually to continue.

Claude is very determined, so would attempt to work around it by removing the file, waiting, and then trying the process again. And then try other variants until it finally succeeded. This was super slow and annoying. Disk space, which is a common culprit, was not the problem. And I couldn’t find any other obvious causes, so I lived with it for a while.

Eventually, Claude hinted at a background process running git status that could be blocking things. I realized that my Claude statusline script was at fault (a git status call in my statusline refresh was setting a lock and blocking other git operations.)

If you run into the same issue, you can set this env var as part of your statusline script to avoid this: GIT_OPTIONAL_LOCKS = 0 (git docs)

Presentation: WordPress in the Newsroom

Posted on July 31, 2014 by Mo Jangda

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Protected: Presentation: 2013 In Review [VIP Workshop 2014]

Posted on April 8, 2014 by Mo Jangda

Presentation: Deploys at WordPress.com VIP

Posted on March 13, 2014 by Mo Jangda

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Deploys at WordPress.com VIP

About me: Mohammad (Mo) Jangda

[email protected] | [email protected] | @mjangda

Code Wrangler at Automattic
Ice Cream Fan

What is WordPress.com?

Hosted platform for running blogs, sites, etc. using WordPress.

Big multisite network.

What is VIP?

WordPress hosting and services for big companies (CNN, TIME, ESPN, CBS, TechCrunch, Williams, etc.)

A VIP site on WordPress.com is the same as a free site, except with some custom code a bit of magic sauce.

The VIP team works with external developers providing code review, developer support, etc.

Fancy Numbers

54 million sites
62 million users
30 million posts (per month)
13 billion pageviews / 400 uniques (per month)
500 million MySQL tables
2500 servers
3+ DCs

How Many Deploys?

Yesterday: 259

VIP: 165
WP.com: 75
Other: 19

How is code deployed on WordPress.com?

Production servers run trunk

– Commit changes to trunk
– Run deploy script
– Deploy script syncs svn mirrors across DCSs and runs `svn up` on all servers



$ deploy wpcom

Going to update from 93786 to 93787 for /public_html/

Syncing wpcom SVN Mirrors

	DFW (1s)...

	IAD (2s)...

	SAT (2s)...

Deploying wpcom  revision 93787

Deploying to static webs

	SAT (1s)...

	IAD (1s)...

	DFW (1s)...

Deploying to dynamic webs

	DFW (5s)...

	IAD (7s)...

	SAT (9s)...

What about VIPs?

Similar to WordPress.com except:

– Code comes from external developers
– Deploy done internally
– We only push the particular folder (code changes are limited to the “theme”)

VIP Numbers

5 Software Engineers; 1 Happiness Engineer; other biz people
7m lines of code (on top of WP.com codebase)
1000s of sites
~100 active developers
Over 140K commits (currently r140321)
70K deploys all time
Avg deploy time (commit => review => deploy): 130 minutes

Challenges

– External developers writing PHP, HTML, and JS so anything is fair game
– Issues on one site can spill over to another (also helps with scaling)

Code Review is Essential

Make sure they’re not doing not-so-good things

Guidelines: http://vip.wordpress.com/documentation/code-review-what-we-look-for/

Challenge: Code Review is hard and time-consuming! Blocks business needs!

Deploy Page

– custom built tool to optimize review process
– Used to track pending commits, review changes, and deploy
– Can send feedback on issues, alert rest of team when issues spotted
– Handy revert commands!
– “real-time”

Pre-Deploy Tests

Run when deploy button is pressed.

Loads up the site against a sandbox server in production with live database (crazy!) and latest code.

Static Analysis

Using custom scanning tools + PHP Code Sniffer to catch things like restricted functions, bad coding patterns/practices, etc.

Coming soon: post-commit tests

Using Jenkins to run tests immediately after commit, instead of on-demand using Sandbox server in production.

Other Tools

– Reference Page with handy revert commands
– IRC Channel piping PHP and MySQL errors from 2 servers
– IRC alerts for internal commit and deploy notifications
– Email and webhooks for external commit and deploy notifications

Future: Scaling

– More developers and automation
– Externally initiated deploys and post-deploy reviews

Thanks!

[email protected] | [email protected] | @mjangda

Hiring, Hiring, Hiring!

VIP Wranglers, VIP Wranglers, VIP Wranglers!
Code Wranglers, Code Wranglers, Code Wranglers!
Designers, Designers, Designers!
Happiness Engineers, Happiness Engineers, Happiness Engineers!

Presentation: Caching; for fun and profit

Posted on June 29, 2013 by Mo Jangda

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Caching; For Fun & Profit

Understanding different caching tools and techniques available to WordPress developers such as the Transient and Object Caching APIs and how/why they can make or break your site.

About me: Mohammad (Mo) Jangda

[email protected] | [email protected] | @mjangda

Toronto, ON
Code Wrangler at WordPress.com VIP (Automattic)
Core Contributor
Ice Cream Fan

Hiring, Hiring, Hiring!

VIP Wranglers, VIP Wranglers, VIP Wranglers!
Code Wranglers, Code Wranglers, Code Wranglers!
Designers, Designers, Designers!
Happiness Engineers, Happiness Engineers, Happiness Engineers!

What is caching?

Caching is more than just installing a plugin to fix your uptime problems.

It’s a way to temporarily store data so that it can be reused.

What is caching?

It’s meant to avoid doing the same expensive computations (fetching from the database, making remote calls, etc.) over and over again.

Put something in a nearby place so can access it more readily.

Can cache all types of things: objects, arrays, strings, integers, etc.

Analogy: A Fireplace, A Lumberjack, and A Pile o’ Wood

A-Pile-of-Logs

So What?

According to Google:

High performance web sites lead to higher visitor engagement, retention and conversions

Translation:
Fast sites == $$$

grillz

What is a slow pageload?

A profit killer.

What is a slow pageload?

Inevitable (as your traffic and site grows).

What is a slow pageload?

An insult to your users. Your users appreciate/want/need/deserve a fast site.

Goal: This, or better

theme-page-generation-time-graph

The Super Secret Technique To A Really Fast Site

REMOVE STUFF!

The Fallback: Caching

Caching: More than just for speed

Caching will help prevent your site from going down if you rely on external services. If Twitter goes down, your site can too.

Caching: More than just for speed

Will force you to think about and write better code. And become a better developer.

The Cache Loop

Most caching interactions follow a simple loop-based pattern:

Get the value we want from cache!
Did we get it?
If “no”: get or generate the value and cache it!
Use the value!

Other patterns exist, but is the simplest, most common one.

The Cache Loop

value = get from cache
if ( value not found ) {
    generate value
    save value in cache 
}
do stuff with value

Different types of caching

Variable/static caching
Object caching
Fragment caching (pieces of rendered HTML or output for a page)
Opcode caching (PHP Acceleration)
Full-page caching (the whole rendered page)
Asset Caching (CDN)

Full-page caching

Your first and easiest line of defence. Store the entire generated page in cache and serve to users when they visit.

* Super Cache
* W3 Total Cache
* Batcache (used on WP.com; pages served in 0.004 seconds)

Harder now that we have more personalized, user-centric sites.

The quality of your code will impact how effective a full-page cache is

Code Quality is important

Caching/optimizing at the application-level is super important.

Will touch on this later.

Opcode Caching

APC, XCache, Zend Optimizer+, etc.

Improves the actual PHP-level load times of your application/site by storing compiled versions of your PHP files.

Can significantly improve load times if your site has thousands of files (or using large plugins like BuddyPress).

Variable Assignments

Is this better?

if ( get_the_terms() ) {
     foreach ( get_the_terms() as $term ) { … }
}

Or this?

$terms = get_the_terms();
if ( $terms ) {
     foreach ( $terms as $term ) { … }
}

Variable Assignments

Variable assignments are a type of caching.

You store a value in memory so it can be re-used.

Caching with the `static` var

Useful if you repeat the same function over and over again but don’t want the value to persist between pageloads.

function x_is_it_true() {
    static $is_it_true;
    if ( ! isset( $is_it_true ) )
        $is_it_true = call_really_expensive_function();
    return $is_it_true;
}

Little did you know…

WordPress has caching built-in!

A built-in, non-persistent caching API.

On any given pageload, you’re going to to need to fetch a single option potentially tens of times. And WordPress tries to optimize for that.

Note: it is non-persistant!*

Here’s how WordPress caches options:

Fetch all autoload = yes options:

SELECT option_name, option_value FROM wptrunk_options WHERE autoload = 'yes'

Add the results to object cache (which is really just a global array)
Next time an option is needed, look in the cache first
If not found, grab from the database and update the array.

Code Snippet from get_option()

$alloptions = wp_load_alloptions(); // wp_load_alloptions fetches autoload = yes

if ( isset( $alloptions[$option] ) ) {
    $value = $alloptions[$option];
} else {
    ...
    $row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );
    ...
}

WordPress caches lots of things for you!

* options
* posts
* users
* queries
* terms
* etc.

Object Caching API

This is the API WordPress uses and makes available to developers:

/**
 * Retrieves the cache contents from the cache by key and group.
 *
 * @param int|string $key What the contents in the cache are called
 * @param string $group Where the cache contents are grouped
 *
 * @return bool|mixed False on failure to retrieve contents or the cache
 *              contents on success
 */
function wp_cache_get( $key, $group = '' ) {

Object Caching API

/**
 * Saves the data to the cache.
 *
 * @param int|string $key What to call the contents in the cache
 * @param mixed $data The contents to store in the cache
 * @param string $group Where to group the cache contents
 * @param int $expire When to expire the cache contents
 *
 * @return bool False on failure, true on success
 */
function wp_cache_set( $key, $data, $group = '', $expire = 0 ) {

Object Caching API

/**
 * Adds data to the cache, if the cache key doesn't already exist.
 *
 * @param int|string $key The cache key to use for retrieval later
 * @param mixed $data The data to add to the cache store
 * @param string $group The group to add the cache to
 * @param int $expire When the cache data should be expired
 *
 * @return bool False if cache key and group already exist, true on success
 */
function wp_cache_add( $key, $data, $group = '', $expire = 0 ) {

Object Caching API

/**
 * Removes the cache contents matching key and group.
 *
 * @param int|string $key What the contents in the cache are called
 * @param string $group Where the cache contents are grouped
 * @return bool True on successful removal, false on failure
 */
function wp_cache_delete( $key, $group = '' ) {

Difference between `wp_cache_add` and `wp_cache_set`?

If the value already exists, add will bail; set will override.

A few other intricacies as well, although, don’t worry about them unless you’re building really big sites.

The Cache Loop: In Action!

// First, check to see if the value is in the cache
$featured_posts = wp_cache_get( 'my-featured-posts' );
 
// Did we find it?
if ( false === $featured_posts ) {
    // Nope! Let's generate and cache it!
    $featured_posts = get_posts( array( 'post__in'  => get_option( 'sticky_posts' ) ) );
    wp_cache_set( 'my-featured-posts', $featured_posts );
}
 
// Cool, now we have our value; let's use it!
foreach ( $featured_posts as $post ) {
...

Warning: Careful with the `false` and error conditions!

You should account for those or be prepared for pain during failures.

$tweets = my_get_twitter_tweets( '#yolo' );
if ( $tweets ) {
    wp_cache_set( 'yolo', $tweets, 'my-tweets' );
}

Better Handling Error Conditions

$tweets = my_get_twitter_tweets( '#yolo' );
if ( $tweets ) {
    wp_cache_set( 'yolo', $tweets, 'my-tweets', MINUTE_IN_SECONDS * 10 );
} else {
    wp_cache_set( 'yolo', array(), 'my-tweets', MINUTE_IN_SECONDS * 1 );
}

Warning: Prefixing rules still apply

If you run into conflicts, you’re gonna have a bad time!

Warning: By default, caching in WordPress in non-persistent.

This means that your cache is emptied and re-built every time a new page is loaded.

Persistent Object Caching

You can make the data persist using an object caching backend like memcached:

Memcached Object Cache

This will retain objects in cache across pageloads, so you don’t need to hit the database again.

There are other caching backends as well like APC.

If you don’t have access to object cache…

Transients

If you’re a plugin/theme author, there’s no guarantee of the environment your users are in and whether persistent object caching is available.

WordPress Transients API helps you cache things without needed a caching backend.

Transients

The data:

a) persists across pageloads; and
b) expires after a set period of time (hence the name).

Useful for things like remote data or data that you know has a limited time span.

The Transients API

function get_transient( $transient ) {}

function set_transient( $transient, $value, $expiration ) {}

function delete_transient( $transient ) {}

The Cache Loop: In Action!

// First, check to see if the value is in the cache
$remote_data = get_transient( 'my-remote-data' );

// Did we find it?
if ( false === $remote_data ) {
    // Nope! Let's fetch and cache it!
    $response = wp_remote_get( 'http://foo.com/file.txt' );
    $remote_data = json_decode( wp_remote_retrieve_body( $response ) );
    set_transient( 'my-remote-data', $remote_data );
}
 
// Cool, now we have our value; let's use it!
foreach ( (array) $remote_data as $tweet ) {
...

Warning: Don’t overuse transients

* they’re stored in the options table and can bloat; and
* they require database calls to fetch.

Famous Last Words

“Oh, don’t worry. I’ll just put it in cache/transient…”

I worry. A lot.

Caching helps but…

You need to be smart about and understand what your application is doing.

A slow query will always be slow regardless of how many layers of caching you add around it.

Cache Stampedes Will Break You

Cache stampede: when a load of requests in succession kick of the same expensive process because all of them hit an empty cache on or around the same time.

Too many lumberjacks chopping the same wood

4111-lumberjacks-nm

Cache Stampede: Solutions

Locking: Prevent the pileup
Async: Separate the cache generation process

…OR FIX (REMOVE) THE DAMN THING!

The Uncached (“cold cache”) Pageload

Optimize for the worst case scenario: aim for the best by optimizing for the worst (although, within realistic means).

Uncached pageloads should be as slim as possible.

The Uncached (“cold cache”) Pageload

Technique: Kill your object cache and examine load time patterns on a few different types of pages:

homepage
category
single
404
any special or complex templates

Examine the Uncached Pageload

What’s the load time like?

If it times out, that’s a red flag.
If the pageload time is inconsistent, that’s a red flag.
If the pageload time is unusually high, that’s a red flag.

Summary

Caching in WordPress is “easy”: many things built-in; many ways to do it
Understanding the intricacies of who, what, when, where to cache is hard!
There’s a lot more to caching than I’ve covered here!
If used well, caching will help keep your site alive, fast, and $$$!

Thanks!

[email protected] | [email protected] | @mjangda

Protected: Presentation: Make It Faster II

Posted on May 15, 2013 by Mo Jangda

Presentation: How to think and work like a VIP Developer

Posted on April 27, 2013 by Mo Jangda

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WordPress in the Newsroom (NASH)

Posted on January 11, 2013 by Mo Jangda

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WordPress in the Newsroom

About me: Mohammad (Mo) Jangda

WordPress.com VIP

~22.5%

Some of the biggest names in media, business, and government

New York Post

TIME.com

Quartz

Re/code

It’s hip to be WordPress

Most Important: Stay Secure

Structured Data

Custom Post Types

Custom Taxonomies

Post Metadata

Media: Easy Embeds

Media: Easy Images/Galleries/Audio/Video

Distraction-free editing

Go Mobile

Post-by-email

Mobile + Real-time

Real-time + Curation

Curation: Zoninator

Getting Social

Plugin: Jetpack

Web-first Workflows

Plugin: Edit Flow

Edit Flow: Calendar

Edit Flow: Custom Statuses

Edit Flow: Editorial Comments

Edit Flow: Everything Else

Knowledgebase: WP-Help

Co-Authors Plus

Co-Authors Plus

Other Options?

Camayak

Your WordPress, Your Way

Bangor Daily News: Google Docs

Thanks!

Deploys at WordPress.com VIP

About me: Mohammad (Mo) Jangda

What is WordPress.com?

What is VIP?

Fancy Numbers

How Many Deploys?

How is code deployed on WordPress.com?

What about VIPs?

VIP Numbers

Challenges

Code Review is Essential

Deploy Page

Pre-Deploy Tests

Static Analysis

Coming soon: post-commit tests

Other Tools

Future: Scaling

Thanks!

Hiring, Hiring, Hiring!

Caching; For Fun & Profit

About me: Mohammad (Mo) Jangda

Hiring, Hiring, Hiring!

What is caching?

What is caching?

Analogy: A Fireplace, A Lumberjack, and A Pile o’ Wood

So What?

According to Google:

Translation:Fast sites == $$$

What is a slow pageload?

What is a slow pageload?

What is a slow pageload?

Goal: This, or better

The Super Secret Technique To A Really Fast Site

The Fallback: Caching

Caching: More than just for speed

Caching: More than just for speed

The Cache Loop

The Cache Loop

Different types of caching

Full-page caching

The quality of your code will impact how effective a full-page cache is

Translation:
Fast sites == $$$

Caching with the `static` var

Difference between `wp_cache_add` and `wp_cache_set`?

Warning: Careful with the `false` and error conditions!

Big site + Lots of traffic
=
:(

Big site + Lots of traffic
+ Good infrastructure
=
:)

Big site + Lots of traffic
+ Good infrastructure
+ VIP Developer(s)
=
:D :D :D :D :D

The Key Question:

How does one become a VIP Developer?

Here’s the secret:

A VIP Developer is great at software development.

Great Software Developers:

Understand and Follow good software development practices

Great Software Developers:

Are platform independant