6.3.2.1 Monitoring XRMEM Cache Using AWR

Automatic Workload Repository (AWR) contains information relating to XRMEM cache. Following are descriptions and examples of the most commonly used sections in the AWR report that contain information about XRMEM cache. By reviewing these sections of the AWR report, administrators can understand the operation of XRMEM cache.

Note that because storage servers cannot account for the RDMA I/Os, the Oracle Database statistics are critical in understanding the use of XRMEM cache. The XRMEM cache statistics in the Exadata-specific sections of the AWR report only include I/Os that as serviced by cellsrv, which are not RDMA I/Os.

Database IOs

A summary of Database IOs may be found in the Single Block Reads section of the AWR report. This summary contains information about the effectiveness of XRMEM cache. The Single Block Reads section is located in the AWR report under Exadata Statistics > Performance Summary.

In the following example, the overwhelming majority of all read I/O requests (approximately 88%) are serviced using RDMA reads to XRMEM cache (cell RDMA reads), at a rate of more than 176,000 per second. Nearly all of the rest are satisfied using non-RDMA XRMEM cache reads (cell xrmem cache read hits), while the remaining reads are serviced by using Exadata Smart Flash Cache (cell flash cache read hits). Notice the massive difference in throughput for each different I/O type, which illustrates the power of XRMEM cache and RDMA.

Figure 6-10 AWR Report: Database IOs

XRMEM Cache Configuration and Space Usage

The XRMEM Cache Configuration section contains summary information including the caching mode (Write-Through or Write-Back) and overall size. The XRMEM Cache Space Usage section provides summary statistics on space usage in XRMEM cache.

The following example shows XRMEM cache configured in Write-Through mode on all cells, with a total size of approximately 1509 GB.

Figure 6-11 AWR Report: XRMEM Cache Configuration

The following example of the XRMEM Cache Space Usage section shows 172 GB of XRMEM cache spread evenly across 3 cells.

Figure 6-12 AWR Report: XRMEM Cache Space Usage

XRMEM Cache User Reads

The XRMEM Cache User Reads section shows information about read requests, read throughput, and read efficiency. Because storage servers cannot account for RDMA I/Os, the statistics only relate to non-RDMA reads processed by cellsrv. Hits are for I/Os satisfied using XRMEM cache, while misses indicate that the data was not in XRMEM cache.

Figure 6-13 AWR Report: XRMEM Cache User Reads

XRMEM Cache Internal Writes

The XRMEM Cache Internal Writes section shows writes to XRMEM cache that are performed by Oracle Exadata System Software. The internal writes are I/Os that populate XRMEM cache.

Figure 6-14 AWR Report: XRMEM Cache Internal Writes