Understanding PHP Memory Limits

memory_limit caps PHP-managed allocation per request or CLI process, not total FPM pool RAM.

What It Does and When to Use It

Read the active per-process PHP memory limit. Current allocations answer how much PHP holds now; peak allocations expose workload spikes that can exceed the process limit.

Requirements, Inputs and Expected Behavior

Confirm the runtime, extension, environment variables, and permissions before running the examples in production. Raising it without calculating worker concurrency can destabilize the host.

Example 1: Basic Operation

Read the active per-process PHP memory limit.

<?php
$limit=ini_get('memory_limit');
echo $limit==='-1'?'Unlimited by PHP':"PHP memory_limit = $limit";

Example 2: Behavior and Validation

Distinguish current memory from peak memory reported by PHP.

<?php
$values=range(1,10000);
echo 'Current: ',memory_get_usage(true),' Peak: ',memory_get_peak_usage(true);

Practical Example: Application Use

Budget batch sizes instead of increasing memory_limit without measuring the workload.

<?php
$bytes=32*1024*1024;
$rows=(int)($bytes/1024);
echo 'Target row budget: ', $rows;

Important Behavior and Edge Cases

The second example highlights: Distinguish current memory from peak memory reported by PHP. The practical example adds: Budget batch sizes instead of increasing memory_limit without measuring the workload.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• memory_limit caps PHP-managed allocation per request or CLI process, not total FPM pool RAM.
• Budget batch sizes instead of increasing memory_limit without measuring the workload.
• Measure the representative workload before changing memory_limit or forcing garbage collection.