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PCOV for large PHP codebases

This is an alternative distribution of PCOV for aggregate coverage of large PHP test suites. It keeps PCOV's fast opcode recording and all upstream APIs, and adds a synchronous native export path that can reuse an immutable executable-line manifest.

Normal PCOV records positive line hits while PHP executes. pcov\collect() later runs Zend control-flow-graph (CFG) discovery to find executable but unexecuted lines and builds the nested PHP coverage array. Repeating that work for many web requests can dominate coverage collection in a large application.

Nothing is forked from PHP-FPM, no work is delegated to another process, and request export remains synchronous. Native full collection is always the correctness fallback. The optimization is designed for coverage aggregated across an entire suite, not for a standalone request report.

Requirements and installation

Release 2.1.2 supports Linux, NTS PHP 8.3, 8.4, and 8.5. It uses the extension name pcov, so it replaces and cannot be loaded beside official PCOV.

Install with PIE, the PHP extension installer:

Or build from source:

Enable it in the dedicated coverage SAPI:

pcov.large_codebase controls manifest export and defaults to 1. Set it to 0 to retain upstream collection behavior without compile fingerprints or native export. Application sources must be immutable during a request and an OPcache generation must not mix deployments; use atomic deployment paths and reset OPcache when switching generations.

Upstream-compatible API

The original API and line-coverage semantics are unchanged:

pcov\waiting(), pcov\memory(), pcov\enabled(), pcov\all, pcov\inclusive, and pcov\exclusive remain available.

Large-codebase workflow

1. Define the deployment identity

The identity must change when application code, dependencies, enabled modules, generated code, or the relevant source inventory changes:

Use authoritative build inputs in place of the generic strings. Timestamps alone are not a deployment identity.

2. Generate an immutable manifest

During one complete reference suite, export full records tagged with that identity:

Build and atomically publish the immutable manifest from all reference records:

The reference suite must load the complete coverage scope. Keep old manifest generations while request records still reference them.

3. Export validated request hits

PCOV validates the runtime identity, every selected loaded file, SHA-256 source fingerprints, and every positive hit. New, changed, unreadable, raced, unknown, or incompatible code synchronously produces a complete full-fallback record. Temporary files are unique and publication uses atomic rename.

4. Merge into the normal PCOV representation

coverage.php returns the normal file => line => -1|1 array. The merger is deterministic and idempotent. It rejects corrupt records, mismatched identities, unknown files or lines, and incomplete fallback cohorts. A fallback is never silently reported as complete; rebuild the immutable manifest from a complete full-discovery suite before publishing the next generation.

See Manifest and record architecture for the identity, validation, fallback, and binary-format contract.

Added API

With no manifest, export() writes complete native coverage. Passing a deployment ID tags that full record for manifest creation. With a manifest and deployment ID, it writes validated hits or a synchronous full fallback. export_stats() exposes diagnostics used by the benchmark suite.

Coverage records use a fixed-width, big-endian, checksummed format (version 1) with strict bounds checking. Records are intentionally tied to an exact PHP_VERSION_ID; regenerate manifests when changing PHP or PCOV versions.

Benchmarks — 2.1.2

Magento

Magento 2.4.8 / PHP 8.3.31, 100 GETs across two routes; median of three rotating rounds. Total time includes requests and coverage merge; export is part of it.

2.1.2 with cache on reduced total time by 50.8% versus official PCOV. Compared with the same 2.1.2 build with cache off, enabling the cache reduced export time by 9.5% and total time by 1.0%, reusing 94/100 records per round. All nine rounds produced identical coverage: 1,434 files and 42,145 executable lines. Measurements.

Synthetic CLI

PHP 8.5.11, 1,500 files, 64,500 executable lines, ten requests per round and ten rotating rounds. The GET cache is inactive in CLI. Total time and CPU include merge.

2.1.2 reduced total time by 8.7% and export time by 91.9% versus official PCOV. Coverage matched in all 20 runs. Summary · Raw rounds.

PCOV 2.1.2 uses an existing manifest in both benchmarks; initial manifest bootstrap is excluded.

Operational limits

• Use this extension only in a dedicated coverage SAPI. Like official PCOV, its executor hooks are not compatible with Xdebug, phpdbg coverage, or other tools replacing the same hooks.
• Sources and active manifests must be immutable. Publish new generations to a new path by atomic rename; never truncate an active manifest.
• Compile-side fingerprints are reused only while canonical path, device, inode, mode, size, nanosecond mtime, and nanosecond ctime still match. A mismatch rereads and hashes the source; uncertainty falls back fully.
• Eval code, unsupported streams, unreadable files, and source races fail closed.
• The merger needs an authoritative complete reference suite to account for files no request loaded and files removed between deployments.
• This release supports Linux NTS only. Export is synchronous and all mutable coverage state remains process-local.

Native Magento GET coverage cache (2.1.2)

Adds native GET coverage reuse and optimizes source hashing, checksums, and merging. Enable the cache with:

Restart PHP and keep your existing pcov\start() / stop() / export() collector unchanged. No PHP cache helper or invalidation calls are needed. Every request still records and validates its actual hits; matching GETs reuse serialized coverage and write a normal record at the requested path. Magento's private/no-store response headers do not prevent this: HTTP responses are not cached. Requires a valid manifest and pcov.large_codebase=1.

The flag defaults to 0. export() reports cache: hit|miss|bypass when enabled. See cache details.