The cachedb jounal sync takes a long time on my system. It takes about 4 minutes. How do I force journal to sync？

my cachedb version:
Cache Running version:
Cache for UNIX (Red Hat Enterprise Linux for x86-64) 2017.1.1 (Build 111U_SU) Tue May 23 2017 13:39:47 EDT

The frequency with which the journal is synced depends on the operating circumstances of the InterSystems IRIS instance involved. 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.