10 Data caching
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This document discusses data caching and its benefits. Caching stores frequently accessed data in a location that has faster access time than the main storage. This provides spatial, temporal, and concurrency optimizations. It discusses where data is cached, from L1 cache to remote networks. Latency numbers are provided to show access times from different storage levels. Issues like cache coherence, eviction policies, and write policies are also covered. The document ends by discussing caching approaches in the BBOX application, including application caching, Hibernate caching, and query caching.
10 Data caching
- 2. CACHING: WHAT FOR? • Spatial optimization: original data is far and slow to retrieve. • Temporal compute. optimization: original data is heavy to • Concurrency optimization: many users request the same data.
- 3. CACHE: WHAT? Client (CPU, web browser...) Cache Main Repository (RAM, disk, web, DB...)
- 4. LATENCY NUMBERS ! ! ! ! ! ! ! ! ! ! ! ! ! Send packet CA->Netherlands->CA 150,000,000 https://gist.github.com/jboner/2841832 ns 150 ms
- 5. LATENCY NUMBERS ! ! ! ! ! ! ! ! ! ! ! Disk seek ! Send packet CA->Netherlands->CA 10,000,000 ns 10 ms! 150,000,000 ns 150 ms https://gist.github.com/jboner/2841832
- 6. LATENCY NUMBERS ! ! ! ! Main memory reference ! ! ! ! ! ! Disk seek ! Send packet CA->Netherlands->CA 100 ns! 10,000,000 ns 10 ms! 150,000,000 ns 150 ms https://gist.github.com/jboner/2841832
- 7. LATENCY NUMBERS ! ! L2 cache reference ! Main memory reference ! ! ! ! ! ! Disk seek ! Send packet CA->Netherlands->CA 7 ns! 100 ns! 10,000,000 ns 10 ms! 150,000,000 ns 150 ms https://gist.github.com/jboner/2841832
- 8. LATENCY NUMBERS L1 cache reference ! L2 cache reference ! Main memory reference ! ! ! ! ! ! Disk seek ! Send packet CA->Netherlands->CA 0.5 ns! 7 ns! 100 ns! 10,000,000 ns 10 ms! 150,000,000 ns 150 ms https://gist.github.com/jboner/2841832
- 9. LATENCY NUMBERS L1 cache reference 0.5 Branch mispredict 5 L2 cache reference 7 Mutex lock/unlock 25 Main memory reference 100 Compress 1K bytes with Google Snappy 3,000 Send 1K bytes over 1 Gbps network 10,000 Read 4K randomly from SSD 150,000 Read 1 MB sequentially from memory 250,000 Round trip within same datacenter 500,000 Read 1 MB sequentially from SSD 1,000,000 Disk seek 10,000,000 Read 1 MB sequentially from disk 20,000,000 Send packet CA->Netherlands->CA 150,000,000 https://gist.github.com/jboner/2841832 ns! ns! ns! ns! ns! ns! ns 0.01 ns 0.15 ns 0.25 ns 0.5 ns 1 ns 10 ns 20 ns 150 ms! ms! ms! ms! ms! ms! ms! ms
- 10. CACHE COHERENCE • Cache data. hit: the cache content must be in sync with the original • Proxy • DNS ask to the original source if their data is up-to-date. cache provide stale data until expiration.
- 11. CACHE EVICTION • Cache miss: the cache eventually gets full. What can be discarded? • LRU (Last Recently Used) • LFU (Least Frequently Used)
- 12. 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 Cache Main Repository
- 13. CACHE: THE BBOX WAY Windows Client Controllers BOs Server DAOs Database
- 14. CACHE: THE BBOX WAY Windows Controllers BOs DAOs Database Application cache Query cache Second level cache First level cache DBMS cache
- 15. HIBERNATE FIRST LEVEL CACHE • Completely • Is automatic and not tunable. flushed at the session’s end (simplifying: at the end of the transaction).
- 16. 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.
- 17. 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.
- 18. 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.
- 19. Next talk: Welcome to Java 7