写入操作可设置过期时间 ， 不设置  使用  namespace 的 default-ttl
读操作不会修改 
如果 某条记录 只有读 没有写的话 ，ttl会不断变小 ，直到过期

写入操作可设置不更新TTL
可设置为-1 ，Never expire  不过期 不会被逐出

TTL 为0或-1的记录不会过期或逐出
TTL 客户端主动设置，否则使用namespace的默认TTL配置
update和touch操作会更新TTL
NSUP （namespace supervisor） 线程 负责 过期 和 逐出操作。
NSUP线程周期运行， 时间间隔通过 nsup-period 参数设置
nsup-period 默认 120s


WritePolicy
public int generation;

expiration
Record expiration. Also known as ttl (time to live).
Seconds record will live before being removed by the server.
		
-2: Do not change ttl when record is updated. Supported by Aerospike server versions >= 3.10.1.
-1: Never expire. Supported by Aerospike server versions >= 3.1.4.
0: Default to namespace configuration variable "default-ttl" on the server.
>0: Actual ttl in seconds.


private static void runTest(IAerospikeClient client,int ttl) throws Exception{
    WritePolicy policy = new WritePolicy();
    policy.expiration = ttl;
    String key = "ttl_test_"+ttl;
    String value = key+"_"+LocalDateTime.now();
    Key k = new Key(namespace, dataSetName, key);
    Bin v = new Bin(bin,Value.get(value));
    policy.expiration = ttl;
    client.put(policy, k,v);	
    Record record = client.get(null, k);	
    System.out.println("record=" + record+",TTL="+record.getTimeToLive());
    Thread.sleep(2000);
    record = client.get(null, k);	
    System.out.println("record=" + record+",TTL="+record.getTimeToLive());
    System.out.println();		
}
		

完整测试代码
https://gitee.com/dyyx/asdemo/blob/master/src/main/java/demo/TTLTest2.java



		
record=(gen:8),(exp:348489010),(bins:(DATA:ttl_test_-2_2020-12-18T18:18:10.530)),TTL=2591280
record=(gen:8),(exp:348489010),(bins:(DATA:ttl_test_-2_2020-12-18T18:18:10.530)),TTL=2591278

record=(gen:8),(exp:0),(bins:(DATA:ttl_test_-1_2020-12-18T18:18:12.578)),TTL=-1
record=(gen:8),(exp:0),(bins:(DATA:ttl_test_-1_2020-12-18T18:18:12.578)),TTL=-1

record=(gen:9),(exp:348489734),(bins:(DATA:ttl_test_0_2020-12-18T18:18:14.597)),TTL=2592000
record=(gen:9),(exp:348489734),(bins:(DATA:ttl_test_0_2020-12-18T18:18:14.597)),TTL=2591998

record=(gen:5),(exp:345897836),(bins:(DATA:ttl_test_100_2020-12-18T18:18:16.616)),TTL=100
record=(gen:5),(exp:345897836),(bins:(DATA:ttl_test_100_2020-12-18T18:18:16.616)),TTL=98

record=(gen:6),(exp:345897938),(bins:(DATA:ttl_test_200_2020-12-18T18:18:18.634)),TTL=200
record=(gen:6),(exp:345897938),(bins:(DATA:ttl_test_200_2020-12-18T18:18:18.634)),TTL=198

record=(gen:7),(exp:345897938),(bins:(DATA:ttl_test_200_2020-12-18T18:18:20.651)),TTL=198