Oracle 参数 DATA_GUARD_SYNC_LATENCY 官方解释，作用，如何配置最优化建议
本站中文解释
DATA_GUARD_SYNC_LATENCY是Oracle数据库的一个参数，它用来控制同步异步复制数据库之间的时延。其值表示在备用数据库上接收副本日志前，能接受多大的时延(以秒为单位)。如果实际时延超过指定时间，则Oracle会报错。
正确设置DATA_GUARD_SYNC_LATENCY参数的建议是，目标是让时延不超多可接受的数值。通常，主数据库服务器和备份数据库服务器之间的通信延时很小。也就是说，这两个服务器之间的延时可能小于DATA_GUARD_SYNC_LATENCY的设置值，在这种情况下，可以设置其值较大一些，以避免复制中遇到报错。
官方英文解释
DATA_GUARD_SYNC_LATENCY controls how many seconds the Log Writer (LGWR) process waits beyond the response of the first in a series of Oracle Data Guard SYNC redo transport mode connections.
| Property | Description |
|---|---|
|
Parameter type |
Integer |
|
Default value |
|
|
Modifiable |
|
|
Modifiable in a PDB |
No |
|
Range of values |
|
|
Basic |
No |
|
Oracle RAC |
The same value must be used on all instances. |
The default value is 0, which means that the LGWR will wait up to the number of seconds specified by the NET_TIMEOUT attribute of the LOG_ARCHIVE_DEST_n parameter for each SYNC standby destination.
For example, in an Oracle Data Guard configuration that has two standbys which receive redo in SYNC mode, you would define LOG_ARCHIVE_DEST_2 and LOG_ARCHIVE_DEST_3 to use SYNC transport with DATA_GUARD_SYNC_LATENCY set to a value of 2 seconds. When redo needs to be sent to the standbys, it is sent to both the LOG_ARCHIVE_DEST_2 and LOG_ARCHIVE_DEST_3 connections in parallel and the LGWR will wait for acknowledgement. If LOG_ARCHIVE_DEST_2 responds with its message acknowledging that the redo has been received first, the LGWR will not wait for LOG_ARCHIVE_DEST_3 to respond for more than 2 extra seconds (DATA_GUARD_SYNC_LATENCY). If LOG_ARCHIVE_DEST_3 does not respond within those 2 seconds the LGWR disconnects from LOG_ARCHIVE_DEST_3, putting it into the error state. Redo continues to be sent to LOG_ARCHIVE_DEST_2 as usual. After the duration of the REOPEN attribute for LOG_ARCHIVE_DEST_3 has elapsed, the LGWR reconnects to LOG_ARCHIVE_DEST_3 and redo transfer continues. In this manner, the maximum impact of having the second SYNC standby would be restricted to 2 seconds more than having only one SYNC standby, while allowing the Oracle Data Guard configuration to maintain the desired protection level.
LGWR will never wait longer than the value of the NET_TIMEOUT attribute of the LOG_ARCHIVE_DEST_n parameter, regardless of the value of DATA_GUARD_SYNC_LATENCY.
See Also:
“LOG_ARCHIVE_DEST_n”
