DynamoDB Cache Engine

AsyncAws.DynamoDb stores cache entries in a DynamoDB table. Configure it in config/bootstrap.php (legacy layout: app/Config/bootstrap.php) or config/core.php:

Cache::config('default', [
    'engine' => 'AsyncAws.DynamoDb',
    'table' => 'DYNAMODB_TABLE_NAME',
    'prefix' => 'myapp_',
    'duration' => '+1 hours',
]);

The engine has the settings of every cache engine (prefix, duration, groups, ...) and these:

Setting	Default	Description
table	(required)	Name of the table. Cache::config() throws a CacheException when it is missing.
keyAttribute	id	Name of the string partition key.
valueAttribute	value	Name of the attribute storing the value.
expiresAttribute	expires	Name of the attribute storing the expiration time (Unix timestamp), used by Time to Live.
consistentRead	false	Use strongly consistent reads.
clientConfig	[]	Options merged into the AsyncAws configuration for this cache, e.g. ['region' => 'us-east-1'].
client	null	An AsyncAws\DynamoDb\DynamoDbClient to use instead of creating one.

• Integers are stored as numbers, so Cache::increment() and Cache::decrement() are atomic. Like MemcachedEngine, they fail (return false) when the key does not exist or has expired. Other values are serialized and stored as binary.
• A duration of 0 writes items that never expire.
• Expired items are never returned. Enable Time to Live on the table with the expires attribute so that DynamoDB removes them; gc() does nothing.
• Cache::clear() scans the whole table and deletes the items whose key starts with the prefix of the configuration (only the expired ones with Cache::clear(true)). A scan reads, and is charged for, every item of the table, so give each application its own prefix, or its own table, and do not call it often.
• Groups work like those of RedisEngine: each group has a version number stored in the table, and Cache::clearGroup() increments it. The old entries stay in the table until they expire.
• An item is limited to 400 KB. A larger value is not written: Cache::write() returns false and an error is logged.
• Failed requests are logged to the cache scope and the operation returns false.

The items are the same as those of the Aws.DynamoDb engine of pieceofcake2/aws, so both engines can use the same table.

Creating the Table

The table needs a string partition key named id (keyAttribute). createTable() creates it with on-demand capacity and enables Time to Live:

Cache::engine('default')->createTable();

Or with the AWS CLI:

aws dynamodb create-table --table-name DYNAMODB_TABLE_NAME \
    --attribute-definitions AttributeName=id,AttributeType=S \
    --key-schema AttributeName=id,KeyType=HASH \
    --billing-mode PAY_PER_REQUEST
aws dynamodb update-time-to-live --table-name DYNAMODB_TABLE_NAME \
    --time-to-live-specification "Enabled=true,AttributeName=expires"