1. DATA CACHING
Talk 10

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