max_execution_time & set_time_limit()

TL;DR

Explanation

max_execution_time (default 30s) measures CPU time consumed by the PHP process, not wall-clock time. Blocking I/O (sleep, DB queries, HTTP requests) does NOT count. This means a script making many slow DB calls can run for minutes without hitting the limit. set_time_limit(N) resets the timer from the current point. CLI scripts have max_execution_time=0 (unlimited) by default. The fatal error it produces is uncatchable. For long operations: use background jobs/queues, call set_time_limit() in loops, or use CLI with time limits managed by the OS.

Common Misconception

Why It Matters

Common Mistakes

• Using set_time_limit(0) in web requests — allows infinite execution.
• Assuming max_execution_time protects against slow DB queries.
• Not using background jobs for operations known to exceed 30s.

Code Examples

// In a web controller:
set_time_limit(0); // Disable limit for 'safety'
foreach ($millionRows as $row) { processRow($row); }

// In a CLI command or queue worker:
set_time_limit(3600); // 1 hour for this operation

// Reset per chunk to avoid single-chunk timeout:
foreach (array_chunk($rows, 500) as $chunk) {
    set_time_limit(60); // 60s per chunk
    processChunk($chunk);
}

References

• ↗ https://www.php.net/manual/en/function.set-time-limit.php

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