Configuration (php.ini)

APCu's behavior is controlled by several php.ini directives. These are typically set in your main php.ini file or a loaded configuration file like apcu.ini.

Directive	Default	Changeable	Description
apc.enabled	1	PHP_INI_SYSTEM	Toggles APCu on or off. Set to 0 to disable the extension entirely.
apc.shm_size	32M	PHP_INI_SYSTEM	The size of the shared memory segment in megabytes (M) or gigabytes (G). This is the total memory available for caching.
apc.entries_hint	0	PHP_INI_SYSTEM	A hint for the number of distinct variables to store. Set this to the approximate number of keys you expect to cache to optimize hash table performance. If 0, a default is calculated based on shm_size.
apc.ttl	0	PHP_INI_SYSTEM	The default Time-To-Live (in seconds) for cache entries. If an entry is not accessed for this duration, it becomes a candidate for cleanup. 0 means no global TTL.
apc.gc_ttl	3600	PHP_INI_SYSTEM	The number of seconds a cache entry can live in the garbage-collection list.
apc.smart	0	PHP_INI_SYSTEM	Controls the aggressiveness of cache clearing when memory is full. A higher value makes full cache wipes more likely.
apc.enable_cli	0	PHP_INI_SYSTEM	If 0 (default), APCu is disabled in the PHP CLI environment. Set to 1 to enable it for command-line scripts.
apc.slam_defense	0	PHP_INI_SYSTEM	If non-zero, helps prevent cache slams (dog-piling) by dropping write attempts for the same key within a very short time window. Note: As of 5.1.14, this defaults to 0 (off) due to potential issues.
apc.use_request_time	0	PHP_INI_ALL	If 1, uses the SAPI request start time for TTL calculations instead of the system time. Useful for deterministic testing.
apc.serializer	php	PHP_INI_SYSTEM	Specifies the serializer to use for complex variables. Defaults to PHP's built-in serializer. Can be set to igbinary if the igbinary extension is installed.
apc.preload_path	NULL	PHP_INI_SYSTEM	Specifies a directory to scan for .data files to preload into the cache on startup. (Not available in ZTS builds).
apc.coredump_unmap	0	PHP_INI_SYSTEM	If 1, APCu will attempt to unmap the shared memory segment on a crash to prevent it from being included in a core dump.
apc.mmap_file_mask	NULL	PHP_INI_SYSTEM	(If using mmap) An mktemp-style file mask for creating a file-backed memory map (e.g., /tmp/apc.XXXXXX). If NULL, uses anonymous mapping.
apc.mmap_hugepage_size	0	PHP_INI_SYSTEM	(If using mmap on Linux) The size of hugepages to request for the shared memory segment. 0 disables explicit hugepage use.