WordPress Performance Optimization

Comprehensive guide for optimizing WordPress performance: database queries, caching layers, hooks, AJAX, assets, profiling, and anti-pattern detection.

When to Use

• Reviewing code for performance issues in themes or plugins
• Debugging slow page loads, timeouts, or 500 errors
• Optimizing WP_Query or database operations
• Implementing or auditing caching strategy
• Preparing for high-traffic events (launch, sale, viral moment)
• Investigating memory exhaustion or database locks
• Profiling backend performance without a browser

---

1. Database & WP_Query Optimization

Full code examples: resources/database-queries.md

WP_Query Review Checklist

• posts_per_page is set (never -1)
• no_found_rows => true when not paginating
• fields => 'ids' when only IDs needed
• update_post_meta_cache => false if meta not used
• update_post_term_cache => false if terms not used
• Date limits on archive queries
• include_children => false if child terms not needed
• No post__not_in with large arrays
• No meta_query on meta_value (use taxonomy or key presence)
• Results cached with wp_cache_set if repeated

EXPLAIN Indicators

Column	Good Value	Bad Value
type	const, eq_ref, ref, range	ALL (full table scan)
key	Named index	NULL (no index used)
rows	Small number	Large number
Extra	Using index	Using filesort, Using temporary

---

2. Caching Layers

Full code examples: resources/caching-patterns.md

Caching Architecture

User Request
    |
[ CDN / Edge Cache ]       -- Full page HTML, static assets
    |
[ Page Cache (Varnish) ]   -- Bypassed by: cookies, POST, query params
    |
[ Object Cache (Redis) ]   -- DB query results, transients, computed data
    |
[ Database (MySQL) ]       -- InnoDB buffer pool

TTL Strategy

Content Type	Recommended TTL
Homepage	5-15 minutes
Archive pages	15-60 minutes
Single posts	1-24 hours
Static pages	24+ hours
Media files	1 year (versioned)

Page Cache Bypass Triggers (Avoid): session_start(), setcookie() on public pages, POST for read ops, unique query params (UTM/fbclid).

Memcached vs Redis

Feature	Memcached	Redis
Speed	Slightly faster	Fast
Data types	String only	Strings, lists, sets, hashes
Persistence	No	Optional
Memory efficiency	Higher	Lower
Cache groups	Limited	Full support (flush_group)

Recommendation: Use what your host provides. Redis if you need advanced features (groups, persistence).

---

3. Hooks & Actions Anti-Patterns

Full code examples: resources/hooks-ajax-assets.md

• Expensive code on init / wp_loaded (WARNING): HTTP calls or heavy computation on every request. Cache results or move to a later, scoped hook.
• Database writes on frontend page loads (CRITICAL): DB writes on every page view. Buffer in object cache, flush via cron.
• Missing conditional loading (WARNING): Code runs on admin and frontend when only one is needed. Use template_redirect or guard with is_admin().

---

4. AJAX & External Requests

Full code examples: resources/hooks-ajax-assets.md

• admin-ajax.php for public endpoints (WARNING): Loads full WP admin bootstrap. Use REST API instead.
• AJAX polling with setInterval (CRITICAL): Self-DDoS. Use WebSockets, SSE, or exponential backoff.
• Uncached wp_remote_get (WARNING): Blocks render, no timeout. Cache response and set timeout.
• Synchronous external API calls on page load: Move heavy remote work to cron/queue.

---

5. Asset Loading

Full code examples: resources/hooks-ajax-assets.md

• Assets loaded globally (WARNING): Enqueue conditionally with is_page() / is_singular().
• Render-blocking scripts (INFO): Use 'strategy' => 'defer' (WordPress 6.3+).
• Full library imports (WARNING): Import only needed modules (e.g., lodash/map instead of lodash).
• Missing version strings (INFO): Use a THEME_VERSION constant for cache busting.

---

6. Transients & Options

Large Autoloaded Options (WARNING)

All autoloaded options load on every request into alloptions cache. Disable autoload for large or infrequently accessed data using add_option( ..., '', 'no' ) or update_option( ..., false ).

WP-CLI diagnostic:

wp option list --autoload=on --fields=option_name,size_bytes --format=table | sort -k2 -n | tail -20

---

7. WP-Cron

Full code examples: resources/hooks-ajax-assets.md

• Default WP-Cron fires on page requests, adding latency to real users. Disable with DISABLE_WP_CRON and use a server crontab.
• Long-running cron callbacks (CRITICAL): Process in batches with reschedule, never all records at once.
• Always check wp_next_scheduled() before wp_schedule_event() to avoid duplicate schedules.

---

8. Uncached Function Calls

Caching wrapper code: resources/hooks-ajax-assets.md

These WordPress functions query the database on every call without internal caching:

Function	Issue	Fix
url_to_postid()	Full posts table scan	Wrap with wp_cache
attachment_url_to_postid()	Expensive meta lookup	Wrap with wp_cache
count_user_posts()	COUNT query per call	Cache per user
get_adjacent_post()	Complex query	Cache or avoid in loops
wp_oembed_get()	External HTTP + parsing	Cache with transient
wp_old_slug_redirect()	Meta table lookup	Cache result

---

9. Profiling & Measurement

WP-CLI Profiling Commands

# Install if missing:
wp package install wp-cli/profile-command

# Stage overview:
wp profile stage --fields=stage,time,cache_ratio --url=https://example.com/

# Find slow hooks:
wp profile hook --spotlight --url=https://example.com/

# Drill into a specific hook:
wp profile hook init --spotlight

WP-CLI Doctor (Quick Diagnostics)

wp package install wp-cli/doctor-command
wp doctor check
# Checks: autoload-options-size, SAVEQUERIES, WP_DEBUG, cron duplicates, etc.

Server-Timing Headers

With Performance Lab plugin enabled:

curl -sS -D - https://example.com/ -o /dev/null | grep -i "server-timing:"

Query Monitor (Headless via REST)

Authenticate with Application Password, then inspect x-qm-* response headers or use ?_envelope to get qm property with DB queries, cache stats, HTTP API timing.

Performance Targets

Metric	Target	Investigate
Page generation	< 200ms	> 500ms
TTFB	< 200ms	> 500ms
Database queries	< 50	> 100
Duplicate queries	0	> 5
Slowest query	< 50ms	> 100ms
Object cache hits	> 90%	< 80%
Total query time	< 100ms	> 500ms

---

10. Platform-Specific Guidance

Platform	Object Cache	Key Notes
WordPress VIP	Built-in	Use wpcom_vip_* helpers; page cache at edge; strict code review
WP Engine	Built-in	EverCache page cache; Redis object cache; purge API available
Pantheon	Built-in	Redis object cache; Varnish page cache; Fastly CDN
Self-hosted + Redis	Manual setup	Install wp-redis or object-cache-pro; configure TTLs
Shared hosting	Usually none	Transients fall back to DB; be extra cautious with unbounded queries

---

11. Anti-Pattern Quick Reference

#	Pattern	Severity	Fix
1	posts_per_page => -1	CRITICAL	Set limit, paginate
2	query_posts()	CRITICAL	Use WP_Query or pre_get_posts
3	session_start() on frontend	CRITICAL	Remove or restrict to logged-in users
4	setInterval + fetch/ajax	CRITICAL	WebSockets, SSE, or backoff polling
5	DB writes on every page load	CRITICAL	Buffer in cache, flush via cron
6	intval($falsy) in query args	CRITICAL	Validate before querying
7	N+1 queries in loops	CRITICAL	update_postmeta_cache() / batch
8	Long-running cron callbacks	CRITICAL	Batch processing with reschedule
9	Redirect loops	CRITICAL	Debug with x-redirect-by header
10	cache_results => false	WARNING	Remove (let WP cache results)
11	LIKE '%term%' (leading wildcard)	WARNING	Trailing wildcard or search engine
12	post__not_in large arrays	WARNING	Fetch extra, filter in PHP
13	meta_query on meta_value	WARNING	Use taxonomy or key EXISTS
14	Uncached wp_remote_get	WARNING	Cache response, set timeout
15	$.post() for read operations	WARNING	Use GET (cacheable)
16	add_option without autoload=no	WARNING	Set autoload to 'no' for large data
17	setcookie() on public pages	WARNING	JS cookies or restrict scope
18	url_to_postid() uncached	WARNING	Wrap with wp_cache
19	admin-ajax.php for public use	WARNING	Use REST API
20	Dynamic transient keys without obj cache	WARNING	Use wp_cache_set directly
21	in_array() without strict, large array	WARNING	isset() on associative array
22	Expensive code on init hook	WARNING	Use template_redirect or guard
23	Assets loaded globally	WARNING	Conditional wp_enqueue_script
24	get_template_part in large loops	WARNING	Cache rendered output
25	wp_schedule_event without wp_next_scheduled	WARNING	Check before scheduling
26	POST infinite scroll	WARNING	Use GET requests (cacheable)
27	Full lodash import	WARNING	Import specific modules
28	Missing no_found_rows (non-paginated)	INFO	Add 'no_found_rows' => true
29	Missing script version string	INFO	Use THEME_VERSION constant
30	Missing defer/async strategy	INFO	Use 'strategy' => 'defer' (WP 6.3+)

---

12. Search Patterns for Quick Detection

# Critical issues
grep -rn "posts_per_page.*-1\|numberposts.*-1" .
grep -rn "query_posts\s*(" .
grep -rn "session_start\s*(" .
grep -rn "setInterval.*fetch\|setInterval.*ajax" .

# DB writes on frontend
grep -rn "update_option\|add_option" . | grep -v "admin\|activate\|install"

# Uncached expensive functions
grep -rn "url_to_postid\|attachment_url_to_postid\|count_user_posts" .

# External HTTP without caching
grep -rn "wp_remote_get\|wp_remote_post" .

# Asset loading issues
grep -rn "wp_enqueue_script\|wp_enqueue_style" . | grep -v "is_page\|is_singular\|is_admin"

# Transient misuse
grep -rn "set_transient.*\\\$" .

# WP-Cron issues
grep -rn "wp_schedule_event" . | grep -v "wp_next_scheduled"

---

Severity Definitions

Severity	Description
Critical	Will cause failures at scale (OOM, 500s, DB locks)
Warning	Degrades performance under load
Info	Optimization opportunity

Output Format

When reporting findings, structure as:

## Performance Review: [filename/component]

### Critical Issues
- **Line X**: [Issue] - [Explanation] - [Fix]

### Warnings
- **Line X**: [Issue] - [Explanation] - [Fix]

### Recommendations
- [Optimization opportunities]

### Summary
- Total issues: X Critical, Y Warnings, Z Info
- Estimated impact: [High/Medium/Low]