B2C Custom Caches Skill

B2C Custom Caches

Custom caches improve code performance by storing data that is expensive to calculate, takes a long time to retrieve, or is accessed frequently. Caches are defined in JSON files within cartridges and accessed via the Script API.

When to Use Custom Caches

| Use Case | Example | |----------|---------| | Expensive calculations | Check if any variation product is on sale for base product display | | External system responses | Cache in-store availability or prices from external APIs | | Configuration settings | Store configuration data from JSON files or external sources | | Frequently accessed data | Product attributes, category data, site preferences |

Limitations

| Constraint | Value | |------------|-------| | Total memory per app server | ~20 MB for all custom caches | | Max caches per code version | 100 | | Max entry size | 128 KB | | Supported value types | Primitives, arrays, plain objects, null (not undefined) | | Cross-server sync | None (caches are per-application-server) |

Defining a Custom Cache

File Structure

my_cartridge/
├── package.json       # References caches.json
└── caches.json        # Cache definitions

package.json

Add a caches entry pointing to the cache definition file:

{
  "name": "my_cartridge",
  "caches": "./caches.json"
}

caches.json

Define caches with unique IDs and optional expiration:

{
  "caches": [
    {
      "id": "ProductAttributeCache"
    },
    {
      "id": "ExternalPriceCache",
      "expireAfterSeconds": 300
    },
    {
      "id": "SiteConfigCache",
      "expireAfterSeconds": 60
    }
  ]
}

| Property | Required | Description | |----------|----------|-------------| | id | Yes | Unique ID across all cartridges in code version | | expireAfterSeconds | No | Maximum seconds an entry is retained |

Using Custom Caches

Script API Classes

| Class | Description | |-------|-------------| | dw.system.CacheMgr | Entry point for accessing defined caches | | dw.system.Cache | Cache instance for storing and retrieving entries |

Basic Usage

var CacheMgr = require('dw/system/CacheMgr');

// Get a defined cache
var cache = CacheMgr.getCache('ProductAttributeCache');

// Get value (returns undefined if not found)
var value = cache.get('myKey');

// Store value directly
cache.put('myKey', { data: 'value' });

// Remove entry
cache.invalidate('myKey');

Recommended Pattern: get with Loader

Use get(key, loader) to automatically populate the cache on miss:

var CacheMgr = require('dw/system/CacheMgr');
var Site = require('dw/system/Site');

var cache = CacheMgr.getCache('SiteConfigCache');

// Loader function called only on cache miss
var config = cache.get(Site.current.ID + '_config', function() {
    // Expensive operation - only runs if not cached
    return loadConfigurationFromFile(Site.current);
});

Scoped Cache Keys

Include scope identifiers in keys to separate entries by context:

var CacheMgr = require('dw/system/CacheMgr');
var Site = require('dw/system/Site');

var cache = CacheMgr.getCache('ProductCache');

// Site-scoped key
var siteKey = Site.current.ID + '_' + productID;
var productData = cache.get(siteKey, loadProductData);

// Catalog-scoped key
var catalogKey = 'catalog_' + catalogID + '_' + productID;
var catalogData = cache.get(catalogKey, loadCatalogData);

// Locale-scoped key
var localeKey = request.locale + '_' + contentID;
var content = cache.get(localeKey, loadLocalizedContent);

Cache Methods

| Method | Description | |--------|-------------| | get(key) | Returns cached value or undefined | | get(key, loader) | Returns cached value or calls loader, stores result | | put(key, value) | Stores value directly (overwrites existing) | | invalidate(key) | Removes entry for key |

Best Practices

Do

Use get(key, loader) pattern for automatic population
Include scope (site, catalog, locale) in cache keys
Set appropriate expireAfterSeconds for time-sensitive data
Handle cache misses gracefully (data may be evicted anytime)
Use descriptive cache IDs

Don't

Include personal user data in cache keys (keys may appear in logs)
Store Script API objects (only primitives and plain objects)
Rely on cache entries existing (no persistence guarantee)
Expect cross-server cache synchronization
Store undefined values (use null instead)

Cache Invalidation

Caches are automatically cleared when:

Any file in the active code version changes
A new code version is activated
Data replication completes
Code replication completes

Manual invalidation only affects the current application server:

var cache = CacheMgr.getCache('MyCache');

// Invalidate single entry (current app server only)
cache.invalidate('myKey');

// Storing undefined has same effect as invalidate
cache.put('myKey', undefined);

Common Patterns

Caching External API Responses

var CacheMgr = require('dw/system/CacheMgr');
var LocalServiceRegistry = require('dw/svc/LocalServiceRegistry');

var priceCache = CacheMgr.getCache('ExternalPriceCache');

function getExternalPrice(productID) {
    return priceCache.get('price_' + productID, function() {
        var service = LocalServiceRegistry.createService('PriceService', {
            createRequest: function(svc, args) {
                svc.setRequestMethod('GET');
                svc.addParam('productId', args.productID);
                return null;
            },
            parseResponse: function(svc, response) {
                return JSON.parse(response.text);
            }
        });

        var result = service.call({ productID: productID });
        return result.ok ? result.object : null;
    });
}

Caching Expensive Calculations

var CacheMgr = require('dw/system/CacheMgr');

var saleCache = CacheMgr.getCache('ProductSaleCache');

function isProductOnSale(masterProduct) {
    return saleCache.get('sale_' + masterProduct.ID, function() {
        var variants = masterProduct.variants.iterator();
        while (variants.hasNext()) {
            var variant = variants.next();
            if (isInPromotion(variant)) {
                return true;
            }
        }
        return false;
    });
}

Configuration Cache with Site Scope

var CacheMgr = require('dw/system/CacheMgr');
var Site = require('dw/system/Site');
var File = require('dw/io/File');
var FileReader = require('dw/io/FileReader');

var configCache = CacheMgr.getCache('SiteConfigCache');

function getSiteConfig() {
    var siteID = Site.current.ID;

    return configCache.get(siteID + '_config', function() {
        var configFile = new File(File.IMPEX + '/src/config/' + siteID + '.json');
        if (!configFile.exists()) {
            return null;
        }

        var reader = new FileReader(configFile);
        var content = reader.getString();
        reader.close();

        return JSON.parse(content);
    });
}

Troubleshooting

| Issue | Cause | Solution | |-------|-------|----------| | Cache not found exception | Cache ID not defined in any caches.json | Add cache definition to caches.json | | Duplicate cache ID error | Same ID used in multiple cartridges | Use unique IDs across all cartridges | | Entry not stored | Value exceeds 128 KB limit | Reduce data size or cache subsets | | Entry not stored | Value contains Script API objects | Use only primitives and plain objects | | Unexpected cache misses | Different app server or cache cleared | Always handle misses gracefully |

Check the custom error log and custom warn log for cache-related messages.

Agent Skills: B2C Custom Caches

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