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Merge pull request #495 from christofferh/feat/cache-aside

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Caching pattern: Cache-Aside
This commit is contained in:
Ilkka Seppälä 2016-10-17 22:49:16 +03:00 committed by GitHub
commit 64bdab46b9
11 changed files with 192 additions and 137 deletions
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1
caching/README.md
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@ -27,3 +27,4 @@ Use the Caching pattern(s) when
* [Write-through, write-around, write-back: Cache explained](http://www.computerweekly.com/feature/Write-through-write-around-write-back-Cache-explained)
* [Read-Through, Write-Through, Write-Behind, and Refresh-Ahead Caching](https://docs.oracle.com/cd/E15357_01/coh.360/e15723/cache_rtwtwbra.htm#COHDG5177)
* [Cache-Aside](https://msdn.microsoft.com/en-us/library/dn589799.aspx)

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190
caching/etc/caching.ucls
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@ -1,106 +1,90 @@
<?xml version="1.0" encoding="UTF-8"?>
<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
realizations="true" associations="true" dependencies="false" nesting-relationships="true">
<class id="1" language="java" name="main.java.com.wssia.caching.App" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/App.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="249" y="150"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
<class-diagram version="1.1.11" icons="true" automaticImage="PNG" always-add-relationships="false"
generalizations="true" realizations="true" associations="true" dependencies="false" nesting-relationships="true"
router="FAN">
<class id="1" language="java" name="com.iluwatar.caching.CacheStore" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/CacheStore.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="322" y="444"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="2" language="java" name="com.iluwatar.caching.LruCache" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/LruCache.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="700" y="446"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<enumeration id="3" language="java" name="com.iluwatar.caching.CachingPolicy" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="943" y="122"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</enumeration>
<class id="4" language="java" name="com.iluwatar.caching.DbManager" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/DbManager.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="1011" y="426"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="5" language="java" name="com.iluwatar.caching.App" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/App.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="304" y="95"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="6" language="java" name="com.iluwatar.caching.AppManager" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/AppManager.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="604" y="122"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="7" language="java" name="com.iluwatar.caching.UserAccount" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/UserAccount.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="1161" y="139"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="2" language="java" name="main.java.com.wssia.caching.AppManager" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/AppManager.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="502" y="163"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="3" language="java" name="main.java.com.wssia.caching.CacheStore" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/CacheStore.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="537" y="436"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<enumeration id="4" language="java" name="main.java.com.wssia.caching.CachingPolicy" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/CachingPolicy.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="789" y="162"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</enumeration>
<class id="5" language="java" name="main.java.com.wssia.caching.DBManager" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/DBManager.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="1137" y="134"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="6" language="java" name="main.java.com.wssia.caching.LRUCache" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/LRUCache.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="884" y="435"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="7" language="java" name="main.java.com.wssia.caching.UserAccount" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/UserAccount.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="1140" y="405"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="8" language="java" name="test.java.com.wssia.caching.AppTest" project="CachingPatterns"
file="/CachingPatterns/src/test/java/com/wssia/caching/AppTest.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="251" y="374"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<association id="9">
<end type="SOURCE" refId="2" navigable="false">
<attribute id="10" name="cachingPolicy"/>
<multiplicity id="11" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="4" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<association id="12">
<end type="SOURCE" refId="8" navigable="false">
<attribute id="13" name="app"/>
<multiplicity id="14" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="1" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<association id="15">
<end type="SOURCE" refId="3" navigable="false">
<attribute id="16" name="cache"/>
<multiplicity id="17" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="6" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</classifier-display>
<association id="8">
<end type="SOURCE" refId="1" navigable="false">
<attribute id="9" name="cache"/>
<multiplicity id="10" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="2" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<association id="11">
<end type="SOURCE" refId="6" navigable="false">
<attribute id="12" name="cachingPolicy"/>
<multiplicity id="13" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="3" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</classifier-display>
<association-display labels="true" multiplicity="true"/>
</class-diagram>
</class-diagram>

46
caching/src/main/java/com/iluwatar/caching/App.java
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@ -26,22 +26,23 @@ package com.iluwatar.caching;
*
* The Caching pattern describes how to avoid expensive re-acquisition of resources by not releasing
* the resources immediately after their use. The resources retain their identity, are kept in some
* fast-access storage, and are re-used to avoid having to acquire them again. There are three main
* caching strategies/techniques in this pattern; each with their own pros and cons. They are:
* fast-access storage, and are re-used to avoid having to acquire them again. There are four main
* caching strategies/techniques in this pattern; each with their own pros and cons. They are;
* <code>write-through</code> which writes data to the cache and DB in a single transaction,
* <code>write-around</code> which writes data immediately into the DB instead of the cache, and
* <code>write-around</code> which writes data immediately into the DB instead of the cache,
* <code>write-behind</code> which writes data into the cache initially whilst the data is only
* written into the DB when the cache is full. The <code>read-through</code> strategy is also
* included in the mentioned three strategies -- returns data from the cache to the caller <b>if</b>
* it exists <b>else</b> queries from DB and stores it into the cache for future use. These
* strategies determine when the data in the cache should be written back to the backing store (i.e.
* Database) and help keep both data sources synchronized/up-to-date. This pattern can improve
* performance and also helps to maintain consistency between data held in the cache and the data in
* the underlying data store.
* written into the DB when the cache is full, and <code>cache-aside</code> which pushes the
* responsibility of keeping the data synchronized in both data sources to the application itself.
* The <code>read-through</code> strategy is also included in the mentioned four strategies --
* returns data from the cache to the caller <b>if</b> it exists <b>else</b> queries from DB and
* stores it into the cache for future use. These strategies determine when the data in the cache
* should be written back to the backing store (i.e. Database) and help keep both data sources
* synchronized/up-to-date. This pattern can improve performance and also helps to maintain
* consistency between data held in the cache and the data in the underlying data store.
* <p>
* In this example, the user account ({@link UserAccount}) entity is used as the underlying
* application data. The cache itself is implemented as an internal (Java) data structure. It adopts
* a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The three
* a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The four
* strategies are individually tested. The testing of the cache is restricted towards saving and
* querying of user accounts from the underlying data store ( {@link DbManager}). The main class (
* {@link App} is not aware of the underlying mechanics of the application (i.e. save and query) and
@ -74,6 +75,7 @@ public class App {
app.useReadAndWriteThroughStrategy();
app.useReadThroughAndWriteAroundStrategy();
app.useReadThroughAndWriteBehindStrategy();
app.useCacheAsideStategy();
}
/**
@ -136,4 +138,26 @@ public class App {
AppManager.find("004");
System.out.println(AppManager.printCacheContent());
}
/**
* Cache-Aside
*/
public void useCacheAsideStategy() {
System.out.println("# CachingPolicy.ASIDE");
AppManager.initCachingPolicy(CachingPolicy.ASIDE);
System.out.println(AppManager.printCacheContent());
UserAccount userAccount3 = new UserAccount("003", "Adam", "He likes food.");
UserAccount userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
UserAccount userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
AppManager.save(userAccount3);
AppManager.save(userAccount4);
AppManager.save(userAccount5);
System.out.println(AppManager.printCacheContent());
AppManager.find("003");
System.out.println(AppManager.printCacheContent());
AppManager.find("004");
System.out.println(AppManager.printCacheContent());
}
}

36
caching/src/main/java/com/iluwatar/caching/AppManager.java
View File

@ -64,12 +64,7 @@ public final class AppManager {
public static void initCachingPolicy(CachingPolicy policy) {
cachingPolicy = policy;
if (cachingPolicy == CachingPolicy.BEHIND) {
Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
@Override
public void run() {
CacheStore.flushCache();
}
}));
Runtime.getRuntime().addShutdownHook(new Thread(CacheStore::flushCache));
}
CacheStore.clearCache();
}
@ -86,6 +81,8 @@ public final class AppManager {
return CacheStore.readThrough(userId);
} else if (cachingPolicy == CachingPolicy.BEHIND) {
return CacheStore.readThroughWithWriteBackPolicy(userId);
} else if (cachingPolicy == CachingPolicy.ASIDE) {
return findAside(userId);
}
return null;
}
@ -100,10 +97,37 @@ public final class AppManager {
CacheStore.writeAround(userAccount);
} else if (cachingPolicy == CachingPolicy.BEHIND) {
CacheStore.writeBehind(userAccount);
} else if (cachingPolicy == CachingPolicy.ASIDE) {
saveAside(userAccount);
}
}
public static String printCacheContent() {
return CacheStore.print();
}
/**
* Cache-Aside save user account helper
*/
private static void saveAside(UserAccount userAccount) {
DbManager.updateDb(userAccount);
CacheStore.invalidate(userAccount.getUserId());
}
/**
* Cache-Aside find user account helper
*/
private static UserAccount findAside(String userId) {
UserAccount userAccount = CacheStore.get(userId);
if (userAccount != null) {
return userAccount;
}
userAccount = DbManager.readFromDb(userId);
if (userAccount != null) {
CacheStore.set(userId, userAccount);
}
return userAccount;
}
}

25
caching/src/main/java/com/iluwatar/caching/CacheStore.java
View File

@ -40,7 +40,7 @@ public class CacheStore {
* Init cache capacity
*/
public static void initCapacity(int capacity) {
if (null == cache) {
if (cache == null) {
cache = new LruCache(capacity);
} else {
cache.setCapacity(capacity);
@ -121,7 +121,7 @@ public class CacheStore {
* Clears cache
*/
public static void clearCache() {
if (null != cache) {
if (cache != null) {
cache.clear();
}
}
@ -153,4 +153,25 @@ public class CacheStore {
sb.append("----\n");
return sb.toString();
}
/**
* Delegate to backing cache store
*/
public static UserAccount get(String userId) {
return cache.get(userId);
}
/**
* Delegate to backing cache store
*/
public static void set(String userId, UserAccount userAccount) {
cache.set(userId, userAccount);
}
/**
* Delegate to backing cache store
*/
public static void invalidate(String userId) {
cache.invalidate(userId);
}
}

4
caching/src/main/java/com/iluwatar/caching/CachingPolicy.java
View File

@ -24,11 +24,11 @@ package com.iluwatar.caching;
/**
*
* Enum class containing the three caching strategies implemented in the pattern.
* Enum class containing the four caching strategies implemented in the pattern.
*
*/
public enum CachingPolicy {
THROUGH("through"), AROUND("around"), BEHIND("behind");
THROUGH("through"), AROUND("around"), BEHIND("behind"), ASIDE("aside");
private String policy;

8
caching/src/main/java/com/iluwatar/caching/DbManager.java
View File

@ -82,7 +82,7 @@ public final class DbManager {
}
return null;
}
if (null == db) {
if (db == null) {
try {
connect();
} catch (ParseException e) {
@ -106,7 +106,7 @@ public final class DbManager {
virtualDB.put(userAccount.getUserId(), userAccount);
return;
}
if (null == db) {
if (db == null) {
try {
connect();
} catch (ParseException e) {
@ -126,7 +126,7 @@ public final class DbManager {
virtualDB.put(userAccount.getUserId(), userAccount);
return;
}
if (null == db) {
if (db == null) {
try {
connect();
} catch (ParseException e) {
@ -148,7 +148,7 @@ public final class DbManager {
virtualDB.put(userAccount.getUserId(), userAccount);
return;
}
if (null == db) {
if (db == null) {
try {
connect();
} catch (ParseException e) {

12
caching/src/main/java/com/iluwatar/caching/LruCache.java
View File

@ -73,7 +73,6 @@ public class LruCache {
}
/**
*
* Remove node from linked list.
*/
public void remove(Node node) {
@ -90,7 +89,6 @@ public class LruCache {
}
/**
*
* Move node to the front of the list.
*/
public void setHead(Node node) {
@ -136,10 +134,11 @@ public class LruCache {
* Invalidate cache for user
*/
public void invalidate(String userId) {
System.out.println("# " + userId + " has been updated! Removing older version from cache...");
Node toBeRemoved = cache.get(userId);
remove(toBeRemoved);
cache.remove(userId);
Node toBeRemoved = cache.remove(userId);
if (toBeRemoved != null) {
System.out.println("# " + userId + " has been updated! Removing older version from cache...");
remove(toBeRemoved);
}
}
public boolean isFull() {
@ -160,7 +159,6 @@ public class LruCache {
}
/**
*
* Returns cache data in list form.
*/
public List<UserAccount> getCacheDataInListForm() {

2
caching/src/main/java/com/iluwatar/caching/UserAccount.java
View File

@ -23,9 +23,7 @@
package com.iluwatar.caching;
/**
*
* Entity class (stored in cache and DB) used in the application.
*
*/
public class UserAccount {
private String userId;

5
caching/src/test/java/com/iluwatar/caching/CachingTest.java
View File

@ -60,4 +60,9 @@ public class CachingTest {
public void testReadThroughAndWriteBehindStrategy() {
app.useReadThroughAndWriteBehindStrategy();
}
@Test
public void testCacheAsideStrategy() {
app.useCacheAsideStategy();
}
}