Thanks, maybe data was deleted at that time.  I set another time,  the data  recovered.  another question is 

A journal sync can be triggered:

  • Once every two (2) seconds if the system is idle.
  • In an ECP-based distributed cache cluster, by the data server when responding to specific requests (for example, $Increment) from the application servers to guarantee ECP semantics.
  • By a TCOMMIT (in synchronous commit mode, which causes the data involved in that transaction to be flushed to disk) if you are using InterSystems IRIS transactions.
  • As part of every database write cycle by the write daemon.
  • When the journal buffer is full.

if how can I set the size of  journal buffer ,  or force journal sync to be triggered every 2s without waiting for the system to be idle?