redis bigkey删除问题

 文章系转载，便于整理和分类，原文地址：https://zhuanlan.zhihu.com/p/266403451

127.0.0.1:6379> debug object key
Value at:0x7fc06c1b1430 refcount:1 encoding:raw serializedlength:1256350 lru:11686193
lru_seconds_idle:20

127.0.0.1:6379> strlen key
(integer) 2247394

del bigkey

public void delBigHash(String bigKey) {
    Jedis jedis = new Jedis(“127.0.0.1”, 6379);
    // 游标
    String cursor = “0”;
    while (true) {
        ScanResult<Map.Entry<String, String>> scanResult = jedis.hscan(bigKey, cursor, new ScanParams().count(100));
        // 每次扫描后获取新的游标
        cursor = scanResult.getStringCursor();
        // 获取扫描结果
        List<Entry<String, String>> list = scanResult.getResult();
        if (list == null || list.size() == 0) {
            continue;
        }
        String[] fields = getFieldsFrom(list);
        // 删除多个field
        jedis.hdel(bigKey, fields);
        // 游标为0时停止
        if (cursor.equals(“0”)) {
            break;
        }
    }
    // 最终删除key
    jedis.del(bigKey);
}

/**
* 获取field数组
* @param list
* @return
*/
private String[] getFieldsFrom(List<Entry<String, String>> list) {
    List<String> fields = new ArrayList<String>();
    for(Entry<String, String> entry : list) {
        fields.add(entry.getKey());
    }
    return fields.toArray(new String[fields.size()]);
}

Redis 2.8 release notes
=======================

** IMPORTANT ** Check the 'Migrating from 2.6 to 2.8' section at the end of
                this file for information about what changed between 2.6 and
                2.8 and how this may affect your application.

--------------------------------------------------------------------------------
Upgrade urgency levels:

LOW:      No need to upgrade unless there are new features you want to use.
MODERATE: Program an upgrade of the server, but it's not urgent.
HIGH:     There is a critical bug that may affect a subset of users. Upgrade!
CRITICAL: There is a critical bug affecting MOST USERS. Upgrade ASAP.
--------------------------------------------------------------------------------

--[ Redis 2.8.6 ] Release date: 13 Feb 2014

/**
 * 刪除 BIG key
 * 应用场景：对于 big key，可以使用 hscan 首先分批次删除，最后统一删除
 * （1）比直接删除的耗时变长，但是不会产生慢操作。
 * （2）新业务实现尽可能拆开，不要依赖此方法。
 * @param key key
 * @param scanCount 单次扫描总数（建议值：100）
 * @param intervalMills 分批次的等待时间（建议值：5）
 */
void removeBigKey(final String key, final int scanCount, final long intervalMills)

JedisCluster jedisCluster = redisClusterTemplate.getJedisClusterInstance();
// 游标初始值为0
String cursor = ScanParams.SCAN_POINTER_START;
ScanParams scanParams = new ScanParams();
scanParams.count(scanCount);
while (true) {
 // 每次扫描后获取新的游标
 ScanResult<Map.Entry<String, String>> scanResult = jedisCluster.hscan(key, cursor, scanParams);
 cursor = scanResult.getStringCursor();
 // 获取扫描结果为空
 List<Map.Entry<String, String>> list = scanResult.getResult();
 if (CollectionUtils.isEmpty(list)) {
  break;
 }
 // 构建多个删除的 key
 String[] fields = getFieldsKeyArray(list);
 jedisCluster.hdel(key, fields);
 // 游标为0时停止
 if (ScanParams.SCAN_POINTER_START.equals(cursor)) {
  break;
 }
 // 沉睡等待，避免对 redis 压力太大
 DateUtil.sleepInterval(intervalMills, TimeUnit.MILLISECONDS);
}
// 执行 key 本身的删除
jedisCluster.del(key);

/**
 * 获取集合的游标。通过游标可以遍历整个集合。
 * ScanOptions 这个类中使用了构造者 工厂方法 单例。 通过它可以配置返回的元素
 * 个数 count  与正则匹配元素 match. 不过count设置后不代表一定返回的就是count个。这个只是参考
 * 意义
 *
 * @param key
 * @param options 
 * @return
 * @since 1.4
 */
Cursor<V> scan(K key, ScanOptions options);

@Autowired
private StringRedisTemplate template;

public void removeBigKey(String key, int scanCount, long intervalMills) throws CacheException {
    final ScanOptions scanOptions = ScanOptions.scanOptions().count(scanCount).build();
    //TRW 避免内存泄漏
 try(Cursor<Map.Entry<Object,Object>> cursor =
                template.opsForHash().scan(key, scanOptions)) {
     if(ObjectUtil.isNotNull(cursor)) {
            // 执行循环删除
            List<String> fieldKeyList = new ArrayList<>();
            while (cursor.hasNext()) {
                String fieldKey = String.valueOf(cursor.next().getKey());
                fieldKeyList.add(fieldKey);
                if(fieldKeyList.size() >= scanCount) {
                    // 批量删除
                    Object[] fields = fieldKeyList.toArray();
                    template.opsForHash().delete(key, fields);
                    logger.info("[Big key] remove key: {}, fields size: {}",
                            key, fields.length);
                    // 清空列表，重置操作
                    fieldKeyList.clear();
                    // 沉睡等待，避免对 redis 压力太大
                    DateUtil.sleepInterval(intervalMills, TimeUnit.MILLISECONDS);
                }
            }
        }
        // 最后 fieldKeyList 中可能还有剩余，不过一般数量不大，直接删除速度不会很慢
  // 执行 key 本身的删除
  this.opsForValueDelete(key);
 } catch (Exception e) {
  // log.error();
 }
}