DATA CACHINGTalk 10

CACHING: WHAT FOR?

•Spatial optimization: original data is far and slow to retrieve.

•Temporal optimization: original data is heavy to compute.

•Concurrency optimization: many users request the same data.

CACHE: WHAT?

Client CacheMain

Repository

(CPU, web browser...) (RAM, disk, web, DB...)

LATENCY NUMBERS!!!!!!!!!!!!!Send packet CA->Netherlands->CA 150,000,000 ns 150 ms

https://gist.github.com/jboner/2841832

LATENCY NUMBERS!!!!!!!!!!!Disk seek 10,000,000 ns 10 ms!!Send packet CA->Netherlands->CA 150,000,000 ns 150 ms

https://gist.github.com/jboner/2841832

LATENCY NUMBERS!!!!Main memory reference 100 ns!!!!!!!Disk seek 10,000,000 ns 10 ms!!Send packet CA->Netherlands->CA 150,000,000 ns 150 ms

https://gist.github.com/jboner/2841832

LATENCY NUMBERS!!L2 cache reference 7 ns!!Main memory reference 100 ns!!!!!!!Disk seek 10,000,000 ns 10 ms!!Send packet CA->Netherlands->CA 150,000,000 ns 150 ms

https://gist.github.com/jboner/2841832

LATENCY NUMBERSL1 cache reference 0.5 ns!!L2 cache reference 7 ns!!Main memory reference 100 ns!!!!!!!Disk seek 10,000,000 ns 10 ms!!Send packet CA->Netherlands->CA 150,000,000 ns 150 ms

https://gist.github.com/jboner/2841832

LATENCY NUMBERSL1 cache reference 0.5 ns!Branch mispredict 5 ns!L2 cache reference 7 ns!Mutex lock/unlock 25 ns!Main memory reference 100 ns!Compress 1K bytes with Google Snappy 3,000 ns!Send 1K bytes over 1 Gbps network 10,000 ns 0.01 ms!Read 4K randomly from SSD 150,000 ns 0.15 ms!Read 1 MB sequentially from memory 250,000 ns 0.25 ms!Round trip within same datacenter 500,000 ns 0.5 ms!Read 1 MB sequentially from SSD 1,000,000 ns 1 ms!Disk seek 10,000,000 ns 10 ms!Read 1 MB sequentially from disk 20,000,000 ns 20 ms!Send packet CA->Netherlands->CA 150,000,000 ns 150 ms

https://gist.github.com/jboner/2841832

CACHE COHERENCE

• Cache hit: the cache content must be in sync with the original data.

• Proxy ask to the original source if their data is up-to-date.

• DNS cache provide stale data until expiration.

CACHE EVICTION

• Cache miss: the cache eventually gets full. What can be discarded?

• LRU (Last Recently Used)

• LFU (Least Frequently Used)

WRITE POLICY

• I changed the data and put it back into the cache.

• Write-through: the data is synchronously pushed to the original source.

• Write back: the data is pushed to the source only when it is requested.

Client CacheMain

Repository

CACHE: THE BBOX WAY

Database

DAOs

BOs

Controllers

Windows

Server

Client

CACHE: THE BBOX WAY

Database

DAOs

BOs

Controllers

Windows

DBMS cacheFirst level cache

Second level cacheQuery cache

Application cache

HIBERNATE FIRST LEVEL CACHE

•Completely automatic and not tunable.

•Is flushed at the session’s end (simplifying: at the end of the transaction).

HIBERNATE SECOND LEVEL CACHE

@Entity!@Indexed!@Table(name = "BOM_PLACE")!@Cacheable!@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)!public class PlaceImpl extends ThingImpl<PlaceImpl, PlaceTO, PlaceStrategy> implements Place {! ...!

• The cache survives the sessions.

• The cache is held and configured by EhCache.

HIBERNATE QUERY CACHE

@CacheIt!@Dao(entity = PlaceImpl.class)!public interface PlaceImplDao extends GenericDao<PlaceImpl, Long> {!! @CacheIt! List<PlaceTO> findTO();!! ...!!!!Criteria c = sessionFactory.getCurrentSession().getCriteria(...);!c.setCacheable(true);!

Works together with the Second level cache.

BBOX APPLICATION CACHE/**! * @author Federico Russo! */!public interface PlaceBO extends ThingBO<Place, PlaceStrategy, PlaceTO> {!! /**! * Ritorna tutti i figli di un certo TO.! */! @PreAuthorize("hasRole('ROLE_READ_PLACES') and hasPermission(#parentTO, 'READ')")! @PostFilter("hasPermission(filterObject, 'READ')")! @Cacheable(cacheName = "places")! Collection<PlaceTO> findChildrenTO(PlaceTO parentTO, String strategyClassName);!! /**! * Rimuove il Component fornito dai magazzini in cui eventualmente sta.! */! @Transactional! @PreAuthorize("hasRole('ROLE_WRITE_PLACES')")! @TriggersRemove(removeAll = true, cacheName = "places")! void removeFromWarehouses(ComponentTO componentTO);!

We’re not using it. We should.

Next talk: Welcome to Java 7