hbase定时memflush PeriodicMemstoreFlusher

PeriodicMemstoreFlusher类 定时判断是否触发memflush，

判断间隔hbase.server.thread.wakefrequency 默认10S

@Override
    protected void chore() {
      for (HRegion r : this.server.onlineRegions.values()) {
        if (r == null)
          continue;
        if (r.shouldFlush()) {
          FlushRequester requester = server.getFlushRequester();
          if (requester != null) {
            long randomDelay = rand.nextInt(RANGE_OF_DELAY) + MIN_DELAY_TIME;
            LOG.info(getName() + " requesting flush for region " + r.getRegionNameAsString() +
                " after a delay of " + randomDelay);
            //Throttle the flushes by putting a delay. If we don't throttle, and there
            //is a balanced write-load on the regions in a table, we might end up
            //overwhelming the filesystem with too many flushes at once.
            requester.requestDelayedFlush(r, randomDelay);
          }
        }
      }
    }

触发条件should Flush方法

boolean shouldFlush() {
    if(this.completeSequenceId + this.flushPerChanges < this.sequenceId.get()) {//防止memstore变化太多
      return true;
    }
    if (flushCheckInterval <= 0) { //disabled
      return false;
    }
    long now = EnvironmentEdgeManager.currentTimeMillis();
    //if we flushed in the recent past, we don't need to do again now
    if ((now - getLastFlushTime() < flushCheckInterval)) {//每次flush间隔时间，hbase.regionserver.optionalcacheflushinterval默认为1小时
      return false;
    }
    //since we didn't flush in the recent past, flush now if certain conditions
    //are met. Return true on first such memstore hit.
    for (Store s : this.getStores().values()) {
      if (s.timeOfOldestEdit() < now - flushCheckInterval) {   //  oldest edit of store  , one hour ago ,  now  有store在一小时钱修改过
        // we have an old enough edit in the memstore, flush
        return true;
      }
    }
    return false;
  }

  1.依照sequeceid，判断memstore没有太多flush，进行flush

  2.比较每次flush的间隔时间，没到时间，不进行flush（单从时间上看，memstore够老）

  3.超过间隔时间，并且有个store的edit超过间隔时间（从用户修改上看，memstore够老）