Fatal error: Uncaught Error: Class "Memcached" not found

# Common log entries
PHP Fatal error:  Uncaught Error: Class "Memcached" not found in /wp-content/object-cache.php
PHP Fatal error:  Uncaught Error: Class "Memcache" not found in /wp-content/object-cache.php

A Memcached object-cache drop-in in wp-content/object-cache.php shows this error when the server lacks the Memcached PHP extension. Some older drop-ins use the Memcache extension instead and show Class "Memcache" not found. Because the drop-in loads before plugins, the whole site stops.

Common causes

References

1. Memcached (PHP.net)
2. WP_Object_Cache (WordPress Developer Resources)

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Errors caused by stale cache files or a lost object-cache backend are handled automatically: the system removes the stuck cache files and, when the cache backend is unreachable, removes the leftover configuration. Fixes are made on a copy of your site in the recovery station and written back only after re-verification passes. In your site’s database, the protected tables (members, comments, orders and form submissions) are copied as structure only. In SSH and FTP mode, the system creates a pre-recovery backup on your host before writing back and restores from it if verification after write-back fails. If the recovery cannot be completed, the recovery fee is refunded in full.

1. Initial assessment: Site URL entry
2. Copy to the recovery station: Work on a copy
3. Diagnosis: Item-by-item checks
4. Recovery and verification: Home and inner pages
5. Write-back or delivery: Only after verification passes