6.3.6 Monitoring PMEM Log
Note:
This topic applies only to Oracle Exadata System Software releases before 23.1.0. Otherwise, see Monitoring XRMEM Log.
Redo log writes are critical database operations and need to complete in a timely manner to prevent load spikes or stalls. Exadata Smart Flash Log is designed to prevent redo write latency outliers. PMEM Log helps to further reduce redo log write latency by using Persistent Memory (PMEM) and Remote Direct Memory Access (RDMA). PMEM Log is available only in selected Exadata X8M and X9M storage server models.
With PMEM Log, database clients send I/O buffers directly to PMEM on the storage servers
using RDMA, thereby reducing transport latency. The cell server
(cellsrv) then writes the redo to Exadata Smart Flash Log (if enabled) and disk at a later time.
Reduced redo log write latency improves OLTP performance, resulting in higher transaction throughput. In cases where PMEM Log is bypassed, Exadata Smart Flash Log can still be used.