1.7.9 about memory used

I just have 3G data in influxdb 1.7.9, but it used 10GB memory, and increasing. I configure tsi1 already，and the data just save for 3 hour. restart service doesn't make it better, but when i deleted series and index, rebuild the tsi index, restart service, it just used 2.5GB, but quickly reach 4GB and increasing。 what can i do to improve it, there may be something wrong。