public void setSync(boolean sync) {
        this.sync = sync;
    }
If true, the write will be flushed from the operating system
buffer cache (by calling WritableFile::Sync()) before the write
is considered complete.  If this flag is true, writes will be
slower.

If this flag is false, and the machine crashes, some recent
writes may be lost.  Note that if it is just the process that
crashes (i.e., the machine does not reboot), no writes will be
lost even if sync==false.

In other words, a DB write with sync==false has similar
crash semantics as the "write()" system call.  A DB write
with sync==true has similar crash semantics to a "write()"
system call followed by "fdatasync()".
jraft-rheakv/rheakv-core/src/main/java/com/alipay/sofa/jraft/rhea/options/RocksDBOptions.java