Need suggestions about ${DRUID_HOME}/var/tmp/baseXXXflush dir useful

I find that there are about 50G+ disk space is used by these dirs. Any ideas about this?

base9217513361689371425flush

base9218734837346810493flush

base9218812791955543529flush

base9221095178891177921flush

base9221227766433123317flush

base9222206402937193263flush

base9222786417462616343flush

base9223141865411121957flush

base922529393163417860flush