PhpSpreadsheet/docs/topics/memory_saving.md

Memory saving

PhpSpreadsheet uses an average of about 1k per cell in your worksheets, so large workbooks can quickly use up available memory. Cell caching provides a mechanism that allows PhpSpreadsheet to maintain the cell objects in a smaller size of memory, or off-memory (eg: on disk, in APCu, memcache or redis). This allows you to reduce the memory usage for large workbooks, although at a cost of speed to access cell data.

By default, PhpSpreadsheet holds all cell objects in memory, but you can specify alternatives by providing your own PSR-16 implementation. PhpSpreadsheet keys are automatically namespaced, and cleaned up after use, so a single cache instance may be shared across several usage of PhpSpreadsheet or even with other cache usages.

To enable cell caching, you must provide your own implementation of cache like so:

$cache = new MyCustomPsr16Implementation();

\PhpOffice\PhpSpreadsheet\Settings::setCache($cache);

A separate cache is maintained for each individual worksheet, and is automatically created when the worksheet is instantiated based on the settings that you have configured. You cannot change the configuration settings once you have started to read a workbook, or have created your first worksheet.

Beware of TTL

As opposed to common cache concept, PhpSpreadsheet data cannot be re-generated from scratch. If some data is stored and later is not retrievable, PhpSpreadsheet will throw an exception.

That means that the data stored in cache must not be deleted by a third-party or via TTL mechanism.

So be sure that TTL is either de-activated or long enough to cover the entire usage of PhpSpreadsheet.

Common use cases

PhpSpreadsheet does not ship with alternative cache implementation. It is up to you to select the most appropriate implementation for your environnement. You can either implement PSR-16 from scratch, or use pre-existing libraries.

One such library is PHP Cache which provides a wide range of alternatives. Refers to their documentation for details, but here are a few suggestions that should get you started.

APCu

Require the packages into your project:

composer require cache/simple-cache-bridge cache/apcu-adapter

Configure PhpSpreadsheet with something like:

$pool = new \Cache\Adapter\Apcu\ApcuCachePool();
$simpleCache = new \Cache\Bridge\SimpleCache\SimpleCacheBridge($pool);

\PhpOffice\PhpSpreadsheet\Settings::setCache($simpleCache);

Redis

Require the packages into your project:

composer require cache/simple-cache-bridge cache/redis-adapter

Configure PhpSpreadsheet with something like:

$client = new \Redis();
$client->connect('127.0.0.1', 6379);
$pool = new \Cache\Adapter\Redis\RedisCachePool($client);
$simpleCache = new \Cache\Bridge\SimpleCache\SimpleCacheBridge($pool);

\PhpOffice\PhpSpreadsheet\Settings::setCache($simpleCache);

Memcache

Require the packages into your project:

composer require cache/simple-cache-bridge cache/memcache-adapter

Configure PhpSpreadsheet with something like:

$client = new \Memcache();
$client->connect('localhost', 11211);
$pool = new \Cache\Adapter\Memcache\MemcacheCachePool($client);
$simpleCache = new \Cache\Bridge\SimpleCache\SimpleCacheBridge($pool);

\PhpOffice\PhpSpreadsheet\Settings::setCache($simpleCache);