PHP fsync() Function: Usage and Examples

Use fsync() when you need to requests synchronization of stream data and metadata to storage in a PHP application. The examples below show the actual operation and its limitations.

What Is fsync() in PHP?

Requests synchronization of stream data and metadata to storage. The exact signature supported by your installation depends on its PHP version and enabled extensions.

Its syntax is:

fsync($stream): bool

Parameters and return value: The parameter types, optional arguments, references, and return type are shown in the signature above. Optional parameters are marked with an ellipsis in this reference signature.

Example 1: Basic Usage

<?php

$stream = tmpfile(); fwrite($stream,"Record"); var_dump(fsync($stream)); fclose($stream);

Output:

bool(true)

Example 2: Different Input or Behavior

<?php

$stream = tmpfile(); fwrite($stream,"Saved
"); fflush($stream); echo fsync($stream) ? "Synchronized" : "Failed"; fclose($stream);

Output:

Synchronized

Practical Example: Applying the Function

<?php

$stream = tmpfile(); $written = fwrite($stream,"Transaction log
"); if ($written !== false && fsync($stream)) echo "Sync requested"; fclose($stream);

Output:

Sync requested

Important Behavior and Edge Cases

Successful synchronization is not a substitute for transactional storage or a durable backup.

Comparison With Related Functions

Common Beginner Mistakes

Key Takeaways

• Requests synchronization of stream data and metadata to storage.
• Successful synchronization is not a substitute for transactional storage or a durable backup.
• fdatasync() focuses on data and necessary metadata; fsync() also syncs metadata.

Use fsync() for the specific operation demonstrated above. Check its prerequisites and handle failure conditions before using it with production data.