redis 缓存穿透 缓存击穿 缓存雪崩
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public class RedisBloomFilter { private static final Logger LOGGER = Logger.getLogger(RedisBloomFilter.class); private static final String BF_KEY_PREFIX = "bf:"; private int numApproxElements; private double fpp; private int numHashFunctions; private int bitmapLength; private JedisResourcePool jedisResourcePool; /** * 构造布隆过滤器。注意:在同一业务场景下,三个参数务必相同 * * @param numApproxElements 预估元素数量 * @param fpp 可接受的最大误差(假阳性率) * @param jedisResourcePool Codis专用的Jedis连接池 */ public RedisBloomFilter(int numApproxElements, double fpp, JedisResourcePool jedisResourcePool) { this.numApproxElements = numApproxElements; this.fpp = fpp; this.jedisResourcePool = jedisResourcePool; bitmapLength = (int) (-numApproxElements * Math.log(fpp) / (Math.log(2) * Math.log(2))); numHashFunctions = Math.max(1, (int) Math.round((double) bitmapLength / numApproxElements * Math.log(2))); } /** * 取得自动计算的最优哈希函数个数 */ public int getNumHashFunctions() { return numHashFunctions; } /** * 取得自动计算的最优Bitmap长度 */ public int getBitmapLength() { return bitmapLength; } } /** * 计算一个元素值哈希后映射到Bitmap的哪些bit上 * * @param element 元素值 * @return bit下标的数组 */ private long[] getBitIndices(String element) { long[] indices = new long[numHashFunctions]; byte[] bytes = Hashing.murmur3_128() .hashObject(element, Funnels.stringFunnel(Charset.forName("UTF-8"))) .asBytes(); long hash1 = Longs.fromBytes( bytes[7], bytes[6], bytes[5], bytes[4], bytes[3], bytes[2], bytes[1], bytes[0] ); long hash2 = Longs.fromBytes( bytes[15], bytes[14], bytes[13], bytes[12], bytes[11], bytes[10], bytes[9], bytes[8] ); long combinedHash = hash1; for (int i = 0; i < numHashFunctions; i++) { indices[i] = (combinedHash & Long.MAX_VALUE) % bitmapLength; combinedHash += hash2; } return indices; } /** * 插入元素 * * @param key 原始Redis键,会自动加上'bf:'前缀 * @param element 元素值,字符串类型 * @param expireSec 过期时间(秒) */ public void insert(String key, String element, int expireSec) { if (key == null || element == null) { throw new RuntimeException("键值均不能为空"); } String actualKey = BF_KEY_PREFIX.concat(key); try (Jedis jedis = jedisResourcePool.getResource()) { try (Pipeline pipeline = jedis.pipelined()) { for (long index : getBitIndices(element)) { pipeline.setbit(actualKey, index, true); } pipeline.syncAndReturnAll(); } catch (IOException ex) { LOGGER.error("pipeline.close()发生IOException", ex); } jedis.expire(actualKey, expireSec); } } /** * 检查元素在集合中是否(可能)存在 * * @param key 原始Redis键,会自动加上'bf:'前缀 * @param element 元素值,字符串类型 */ public boolean mayExist(String key, String element) { if (key == null || element == null) { throw new RuntimeException("键值均不能为空"); } String actualKey = BF_KEY_PREFIX.concat(key); boolean result = false; try (Jedis jedis = jedisResourcePool.getResource()) { try (Pipeline pipeline = jedis.pipelined()) { for (long index : getBitIndices(element)) { pipeline.getbit(actualKey, index); } result = !pipeline.syncAndReturnAll().contains(false); } catch (IOException ex) { LOGGER.error("pipeline.close()发生IOException", ex); } } return result; } public class RedisBloomFilterTest { private static final int NUM_APPROX_ELEMENTS = 3000; private static final double FPP = 0.03; private static final int DAY_SEC = 60 * 60 * 24; private static JedisResourcePool jedisResourcePool; private static RedisBloomFilter redisBloomFilter; @BeforeClass public static void beforeClass() throws Exception { jedisResourcePool = RoundRobinJedisPool.create() .curatorClient("10.10.99.130:2181,10.10.99.132:2181,10.10.99.133:2181,10.10.99.124:2181,10.10.99.125:2181,", 10000) .zkProxyDir("/jodis/bd-redis") .build(); redisBloomFilter = new RedisBloomFilter(NUM_APPROX_ELEMENTS, FPP, jedisResourcePool); System.out.println("numHashFunctions: " + redisBloomFilter.getNumHashFunctions()); System.out.println("bitmapLength: " + redisBloomFilter.getBitmapLength()); } @AfterClass public static void afterClass() throws Exception { jedisResourcePool.close(); } @Test public void testInsert() throws Exception { redisBloomFilter.insert("topic_read:8839540:20190609", "76930242", DAY_SEC); redisBloomFilter.insert("topic_read:8839540:20190609", "76930243", DAY_SEC); redisBloomFilter.insert("topic_read:8839540:20190609", "76930244", DAY_SEC); redisBloomFilter.insert("topic_read:8839540:20190609", "76930245", DAY_SEC); redisBloomFilter.insert("topic_read:8839540:20190609", "76930246", DAY_SEC); } @Test public void testMayExist() throws Exception { System.out.println(redisBloomFilter.mayExist("topic_read:8839540:20190609", "76930242")); System.out.println(redisBloomFilter.mayExist("topic_read:8839540:20190609", "76930244")); System.out.println(redisBloomFilter.mayExist("topic_read:8839540:20190609", "76930246")); System.out.println(redisBloomFilter.mayExist("topic_read:8839540:20190609", "76930248")); } }
127.0.0.1:6379> setnx lock value1 #在键lock不存在的情况下,将键key的值设置为value1 (integer) 1 127.0.0.1:6379> setnx lock value2 #试图覆盖lock的值,返回0表示失败 (integer) 0 127.0.0.1:6379> get lock #获取lock的值,验证没有被覆盖 "value1" 127.0.0.1:6379> del lock #删除lock的值,删除成功 (integer) 1 127.0.0.1:6379> setnx lock value2 #再使用setnx命令设置,返回0表示成功 (integer) 1 127.0.0.1:6379> get lock #获取lock的值,验证设置成功 "value2"
https://www.zhihu.com/question/300767410/answer/1749442787
https://www.cnblogs.com/williamjie/p/11132211.html
https://www.jianshu.com/p/47fd7f86c848
https://www.jianshu.com/p/c2defe549b40
https://blog.csdn.net/womenyiqilalala/article/details/105205532