Oracle _use_adaptive_log_file_sync参数有何作用
在11gr2以前写日志缓冲区到文件方式是通过Post/wait方式,在11gr2开始增加了Polling的方式,在11.2.0.3以前默认还是采用Post/wait方式,
11.2.0.3开始默认是两种方式自动切换。它是通过隐含参数_use_adaptive_log_file_sync进行设置,当值为true时开启自动切换模式。
两种方式:
查询当前log file sync的方式
SQL> select name,value from v$sysstat where name like 'redo sync%';
NAME VALUE
---------------------------------------------------------------- ----------
redo synch time 1467
redo synch time (usec) 14687694
redo synch time overhead (usec) 211354
redo synch time overhead count ( 2ms) 117
redo synch time overhead count ( 8ms) 6
redo synch time overhead count ( 32ms) 4
redo synch time overhead count (128ms) 2
redo synch time overhead count (inf) 0
redo synch fast sync all sleep (usec) 0
redo synch fast sync all sleep count 0
redo synch fast sync all sleep (20us) 0
NAME VALUE
---------------------------------------------------------------- ----------
redo synch fast sync all sleep (40us) 0
redo synch fast sync all sleep (60us) 0
redo synch fast sync all sleep (80us) 0
redo synch fast sync all sleep (100us) 0
redo synch fast sync all sleep (120us) 0
redo synch fast sync all sleep (160us) 0
redo synch fast sync all sleep (240us) 0
redo synch fast sync all sleep (400us) 0
redo synch fast sync all sleep (720us) 0
redo synch fast sync all sleep (inf) 0
redo synch fast sync sleep count 0
NAME VALUE
---------------------------------------------------------------- ----------
redo synch fast sync sleep (usec) 0
redo synch fast sync sleep o/h (usec) 0
redo synch fast sync spin count 0
redo synch fast sync spin (usec) 0
redo synch fast sync backoff count 0
redo synch fast sync backoff (usec) 0
redo synch fast sync backoff o/h (usec) 0
redo synch writes 196
redo synch long waits 1
redo synch poll writes 0
redo synch polls 0
33 rows selected.
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