A constant-time, variable-workload chunking tool with Doctrine2 integration

1.1.0 2014-08-10 23:33 UTC

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Last update: 2021-04-12 09:49:00 UTC


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A small library for dynamic chunking of large operations against an external system, like a database.

A 'chunk' is a unit of work with a target execution time. If each chunk in an iteration begins to take more time than the target to process, the size of future chunks is reduced.

This library also includes utilities for monitoring slave lag on a set of Doctrine2 connections, and can pause chunk processing to wait for replication to catch up. This sort of strategy is taken by tools like pt-online-schema-change in order to complete a process as fast as possible, but without impacting systems under production load.


Basic Usage

use Chunky\Chunk;

$options = [];

$chunk = new Chunk(
    500,     // Initial chunk size
    0.2,     // Target wallclock execution time in seconds

for (/* ... */) {
    $size = $chunk->getEstimatedSize();

    // Process $size records


  • int min: The minimum chunk size to ever return (default 2 * initial estimate)
  • int max: The maximum estimated size to ever return (default 0.01 * initial estimate)
  • float smoothing: The exponential smoothing factor, 0 < s < 1 (default 0.3)

Monitoring Replication Lag

A Chunk class is provided for monitoring MySQL slave lag on a set of slave database servers: ReplicatedChunk. This class is MySQL-specific (because getting the current slave lag is not implemented for other drivers).

use Chunky\ReplicatedChunk;

/* @var Doctrine\DBAL\Connection $conn */
/* @var Doctrine\DBAL\Connection $conn2 */

$chunk = new ReplicatedChunk(500, 0.2, $options);
$chunk->setSlaves([$conn, $conn2]);


  • int max_lag: When replication lag reaches this many seconds, the slave is considered lagged
  • int pause: The number of microseconds to pause for when slave lag is detected (before rechecking lag)
  • int max_pause: The total number of microseconds the chunk will pause for before continuing or throwing an exception
  • boolean continue: Whether to continue if max_pause is reached; default is to throw an exception and not continue


This library can be loaded yourself with PSR4, but you'd usually just install it with Composer. The package name is vend/chunky.