序
本文主要研究一下redis的事务操作
命令
multi与exec
- 命令行
127.0.0.1:6379> multi
OK
127.0.0.1:6379> incr total
QUEUED
127.0.0.1:6379> incr len
QUEUED
127.0.0.1:6379> exec
1) (integer) 2
2) (integer) 2
127.0.0.1:6379> get total
"2"
127.0.0.1:6379> get len
"2"
- lettuce实例
@Test
public void testMultiExec(){
RedisClient client = RedisClient.create("redis://192.168.99.100:6379/0");
StatefulRedisConnection<String, String> connection = client.connect();
RedisCommands<String, String> syncCommands = connection.sync();
syncCommands.set("hello","1");
syncCommands.set("world","2");
syncCommands.multi();
syncCommands.incr("hello");
syncCommands.incr("world");
//DefaultTransactionResult[wasRolledBack=false,result=[1, 2, 1, 3, 1]]
TransactionResult transactionResult = syncCommands.exec();
System.out.println(transactionResult);
System.out.println(syncCommands.get("hello"));
System.out.println(syncCommands.get("world"));
}
部分执行
- 命令行
127.0.0.1:6379> multi
OK
127.0.0.1:6379> set a hello
QUEUED
127.0.0.1:6379> set b world
QUEUED
127.0.0.1:6379> incr a
QUEUED
127.0.0.1:6379> set c part
QUEUED
127.0.0.1:6379> exec
1) OK
2) OK
3) (error) ERR value is not an integer or out of range
4) OK
127.0.0.1:6379> get a
"hello"
127.0.0.1:6379> get b
"world"
127.0.0.1:6379> get c
"part"
- lettuce实例
@Test
public void testMultiExecError(){
RedisClient client = RedisClient.create("redis://192.168.99.100:6379/0");
StatefulRedisConnection<String, String> connection = client.connect();
RedisCommands<String, String> syncCommands = connection.sync();
syncCommands.multi();
syncCommands.set("a","hello");
syncCommands.set("b","world");
syncCommands.incr("a");
syncCommands.set("c","part");
//DefaultTransactionResult[wasRolledBack=false,result=[OK, OK, io.lettuce.core.RedisCommandExecutionException: ERR value is not an integer or out of range, OK, 1]]
TransactionResult transactionResult = syncCommands.exec();
System.out.println(transactionResult);
System.out.println(syncCommands.get("a"));
System.out.println(syncCommands.get("b"));
System.out.println(syncCommands.get("c"));
}
multi与discard
- 命令行
127.0.0.1:6379> set sum 1
OK
127.0.0.1:6379> multi
OK
127.0.0.1:6379> incr sum
QUEUED
127.0.0.1:6379> discard
OK
127.0.0.1:6379> get sum
"1"
- lettuce实例
@Test
public void testMultiDiscard(){
RedisClient client = RedisClient.create("redis://192.168.99.100:6379/0");
StatefulRedisConnection<String, String> connection = client.connect();
RedisCommands<String, String> syncCommands = connection.sync();
syncCommands.incr("key1");
syncCommands.multi();
syncCommands.incr("key1");
//需要有multi才可以执行discard，成功返回OK
String result = syncCommands.discard();
System.out.println(result);
System.out.println(syncCommands.get("key1"));
}
check and set
@Test
public void testWatch(){
RedisClient client = RedisClient.create("redis://192.168.99.100:6379/0");
StatefulRedisConnection<String, String> connection = client.connect();
RedisCommands<String, String> syncCommands = connection.sync();
String key = "key";
syncCommands.watch(key);
//another connection
StatefulRedisConnection<String, String> conn2 = client.connect();
RedisCommands<String, String> syncCommands2 = conn2.sync();
syncCommands2.set(key, "a");
syncCommands.multi();
syncCommands.append(key, "b");
//DefaultTransactionResult [wasRolledBack=true, responses=0]
TransactionResult transactionResult = syncCommands.exec();
System.out.println(transactionResult);
System.out.println(syncCommands.get(key));
}
小结
- reids提供multi exec/discard指令，类似open commit/rollback transaction，不过exec遇到类型操作等错误时不会滚，该成功执行的命令还是成功执行，该失败的还是失败
- multi exec保证的是，只要exec命令有执行成功，则事务中一系列的命令都能执行，如果exec因为网络等问题，server端没有接收到，则事务中的一系列命令都不会被执行
- discard需要在有调用multi的前提下才能使用，该命令会清空事务队列等待执行的命令
- redis提供watch指令，可以配合multi exec来使用，可以实现类似数据库的乐观锁的机制，一旦watch的key被其他client有更新，则整个exec操作失败
