wal wite redo log

ret = WriteFile(file, buf, (DWORD) n, &len, NULL);

innobase_start_or_create_for_mysql

log_reserve_and_write_fast

log_release

mtr_start(

mtr->n_log_recs = 0

static MYSQL_SYSVAR_ULONG(flush_log_at_trx_commit, srv_flush_log_at_trx_commit,   PLUGIN_VAR_OPCMDARG,   "Set to 0 (write and flush once per second),"   " 1 (write and flush at each commit)"   " or 2 (write at commit, flush once per second).",   NULL, NULL, 1, 0, 2, 0);

srv_flush_log_at_trx_commit,