玉面飞龙的BLOG

从等待事件上优化dataguard log传输,可以关注2个等待事件

• wait for SENDREQ:         表示等待网络传输send received redo
• LNS ASYNC end of log: 表示数据库比较idle，等待LGWR写redo

end of log时间越多约好，wait for SENDREQ时间越少越好

相关进程:

RFS：remote file server
On the standby system, the remote file server (RFS) receives redo data over the network from the
LGWR process and writes the redo data to the standby redo log files.

LNSn:
On the primary database, the LGWR process submits the redo data to one or more network server
(LNSn) processes, which then initiate the network I/O in parallel to multiple remote destinations.

MRP:managed recovery process
The managed recovery process (MRP) applies archived redo log files to the physical standby database,
and automatically determines the optimal number of parallel recovery processes at the time it starts.
The number of parallel recovery slaves spawned is based on the number of CPUs available on the
standby server.

LSP:logical standby process
The logical standby process (LSP) uses parallel execution (Pnnn) processes to apply archived redo
log files to the logical standby database, using SQL interfaces.

和LNS相关等待事件

5.9.2.1 ARCn Process Wait Events

For ARCn archival processing, Table 5-3 shows several of the wait events that monitor the time it takes to spawn or delete RFS connections and to send the redo data to the standby database when using ARCH for the transport mode. See Section 5.3.1 for information about ARCn archival processing.

Table 5-3 Wait Events for Destinations Configured with the ARCH Attribute

Wait Event	Monitors the Amount of Time Spent By . . .
ARCH wait on ATTACH	All ARCn processes to spawn an RFS connection.
ARCH wait on SENDREQ	All ARCn processes to write the received redo data to disk as well as open and close the remote archived redo log files.
ARCH wait on DETACH	All ARCn processes to delete an RFS connection.

5.9.2.2 LGWR SYNC Wait Events

For LGWR SYNC archival processing, Table 5-4 shows several of the wait events that monitor the time it takes for the LGWR process on the primary database to:

• Complete writing to the online redo log files on the primary database
• Transmit the redo data to the remote standby destination
• Wait for the redo data to be written to the standby redo log files
• Receive acknowledgment from the remote standby destination

See Section 5.3.2 for information about LGWR SYNC archival processing.

Table 5-4 Wait Events for Destinations Configured with the LGWR SYNC Attributes

Wait Event	Monitors the Amount of Time Spent By . . .
LGWR wait on LNS	The LGWR process waiting to receive messages from the LNSn process.
LNS wait on ATTACH	All network servers to spawn an RFS connection.
LNS wait on SENDREQ	All network servers to write the received redo data to disk as well as open and close the remote archived redo log files.
LNS wait on DETACH	All network servers to delete an RFS connection.

5.9.2.3 LGWR ASYNC Wait Events

For LGWR ASYNC archival processing, Table 5-5 shows several of the wait events that monitor the time it takes to write the redo data to the online redo log files on the primary database. See Section 5.3.2 for information about LGWR ASYNC archival processing.

Table 5-5 Wait Events for Destinations Configured with the LGWR ASYNC Attributes

Wait Event	Monitors the Amount of Time Spent By . . .
LNS wait on DETACH	All network servers to delete an RFS connection.
LNS wait on ATTACH	All network servers to spawn an RFS connection.
LNS wait on SENDREQ	All network servers to write the received redo data to disk as well as open and close the remote archived redo log files.
True ASYNC Control FileTXN Wait	The LNSn process to get hold of the control file transaction during its lifetime.
True ASYNC Wait for ARCH log	The LNSn process waiting to see the archived redo log (if the LNSn process is archiving a current log file and the log is switched out).
Waiting for ASYNC dest activation	The LNSn process waiting for an inactive destination to become active.
True ASYNC log-end-of-file wait