PHP OPcache stores compiled PHP scripts in shared memory so PHP can reuse them instead of repeating compilation work. It is loaded as a Zend extension and configured through PHP’s configuration files. Whether it is active depends on the PHP installation and, importantly, the PHP runtime (SAPI) serving your application.
What PHP OPcache does
When PHP runs a script, it compiles the source into opcodes that the engine can execute. OPcache keeps those compiled scripts in shared memory, allowing later requests to reuse them rather than compile the source again. The PHP Manual describes opcache.enable as “Enables the opcode cache.”
This explains the intended benefit, not a guaranteed speedup: the result depends on the application, workload, and runtime. PHP’s documentation does not establish a universal performance percentage or one ideal memory size.
How OPcache is loaded and enabled
OPcache is a Zend extension. PHP’s installation guidance loads it using the zend_extension directive, but an installation or package may already include and load it. Check the configuration for the PHP runtime you actually use rather than assuming that installing PHP—or enabling OPcache in one configuration file—enables it everywhere.
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For the web application, inspect the PHP runtime used by its web server or process manager. A command-line check reports the CLI runtime, which can use different PHP binaries and configuration from the web runtime.
- Identify the relevant runtime. Determine whether the application runs through a web server module, PHP-FPM, or another SAPI, and identify its PHP version and configuration.
- Check that OPcache is loaded. Review that runtime’s loaded extensions and configuration for the Zend extension. PHP’s installation manual documents the
zend_extensionloading directive: PHP Manual: Installation — OPcache. - Check that it is enabled there. Inspect the effective value of
opcache.enablefor the same runtime. The manual lists a default of1, but an installation can override it. - Verify the result in the application environment. Use an approved diagnostic method for that SAPI, such as a protected PHP information page or runtime status reporting, and remove or restrict diagnostic pages afterward. A CLI result alone does not confirm the web runtime’s status.
What the main OPcache settings control
The PHP Manual’s defaults are reference values, not a universal sizing prescription. Choose configuration based on the scripts and deployment behavior of the specific runtime, then observe its use.
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| Setting | What it controls | Practical implication |
|---|---|---|
opcache.enable |
Enables the opcode cache; the documented default is 1. |
Check the effective setting in the SAPI serving the application. |
opcache.enable_cli |
Enables OPcache for PHP CLI; the documented default is 0. |
CLI caching is separate from the general enable setting. Turn it on only when it suits the command-line workload. |
opcache.memory_consumption |
Shared-memory allocation, in megabytes. | Compare configured memory with actual consumption and the application’s cached scripts; do not treat the manual’s default as a sizing target for every server. |
opcache.interned_strings_buffer |
Memory reserved for interned strings. | Consider it separately from the shared-memory allocation for cached scripts. |
opcache.max_accelerated_files |
Capacity of the script hash table, expressed as a maximum number of keys (and therefore scripts). | PHP rounds configured values to a supported prime capacity and clamps them to its documented range. |
opcache.validate_timestamps |
Whether PHP checks for changes to source-file timestamps. | If checks are disabled, the deployment process must ensure changed code becomes visible, typically through an appropriate cache-reset or runtime-restart practice. |
opcache.revalidate_freq |
How often timestamp validation is performed. | Account for the setting when choosing how quickly source-file changes should be detected. |
For exact version-specific values and descriptions, consult the PHP Manual: Runtime Configuration — OPcache. A useful deployment review compares the PHP version and SAPI, whether OPcache is loaded and enabled there, shared-memory use and script-table capacity, timestamp behavior, and application compatibility.
CLI caching is a separate choice
opcache.enable_cli controls caching for command-line PHP separately from opcache.enable. The manual documents its default as 0. Therefore, OPcache may be active for web requests but not CLI commands, or the reverse if the two environments have different configuration. Check the runtime that runs the workload rather than drawing conclusions from a different SAPI.
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Source changes, deployments, and stale code
Timestamp validation settings affect how OPcache notices changed source files. If opcache.validate_timestamps is disabled, do not assume edits or newly deployed files will be detected automatically; deployments need a deliberate cache invalidation or process-restart approach appropriate to the setup.
The PHP Manual also cautions that file-override checks can risk stale data when timestamp validation is disabled. Avoid combining compatibility-sensitive options without testing the actual deployment behavior.
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Compatibility settings need application testing
Some OPcache options can affect application behavior, not just resource use. PHP warns that disabling saved comments may break frameworks that inspect documentation comments for annotations. The installation guidance recommends testing settings such as disabling saved comments or enabling file override before using them in production.
- Test changes against the framework and libraries actually in use.
- Exercise normal requests, background jobs, and deployment updates where relevant.
- Monitor cache memory use and script capacity after changes rather than relying on a generic recommended value.
See the PHP Manual’s OPcache installation guidance for loading information and compatibility cautions.
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OPcache and PHP JIT are related but distinct
OPcache’s core function is caching compiled opcodes. PHP’s JIT configuration is a separate optimization layer, not another name for opcode caching. The PHP Manual says the JIT setting defaults to disabled as of PHP 8.4.0. Treat JIT as a separate, workload-specific decision; neither enabling OPcache nor changing JIT settings establishes a performance improvement for a particular application.
What to verify before changing production settings
- Confirm PHP version, SAPI, loaded extension, and effective settings for the application’s runtime.
- Check whether OPcache is enabled for web requests and, separately, for CLI jobs that need it.
- Compare allocated shared memory and script-table capacity with observed use.
- Make sure timestamp validation and deployment cache-reset practices agree.
- Test comment-related or file-override changes with the application before production rollout.
PHP Internals published an RFC proposing that OPcache become required for PHP 8.5, but an RFC is a proposal, not proof that the change shipped. The proposal says it would not remove existing INI settings; consult current release documentation before relying on its status: PHP RFC: Make OPcache required.
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