9.6.5 Oracle Exadata System Software I/O Latency Capping for Write Operations

This feature helps eliminate outliers due to slow writes. It prevents write outliers that would otherwise have been visible to applications.

Disks drives, disk controllers, and flash devices are complex computers that can, occasionally, exhibit high latencies while the device is performing an internal maintenance or recovery operation. In addition, devices that are close to failing sometimes exhibit high latencies before they fail. Previously, devices exhibiting high latencies could occasionally cause slow SQL response times. Oracle Exadata System Software I/O latency capping for write operations ensures excellent SQL I/O response times on Oracle Exadata Database Machine by automatically redirecting high latency I/O operations to a mirror copy.

In Oracle Exadata System Software releases 11.2.3.3.1 and 12.1.1.1.1, if Oracle Exadata Database Machine tries to read from a flash device but the latency of the read I/O is longer than expected, the Oracle Exadata System Software automatically redirects the read I/O operations to another storage server (cell). The database server that initiated the read I/O is sent a message that causes the database server to redirect the read I/O to another mirror copy of the data. Any read I/O issued to the last valid mirror copy of the data is not redirected.

In Oracle Exadata System Software release 12.1.2.1.0, if a write operation encounters high latency, then Oracle Exadata System Software automatically redirects the write operation to another healthy flash device on the same storage server. After the write completes successfully, the write I/O is acknowledged as successful to the database server, thereby eliminating the write outlier.

Requirements:.

• Minimum software:

  • Oracle Database 11g release 2 (11.2) Monthly Database Patch For Exadata (June 2014 - 11.2.0.4.8)

  • Oracle Grid Infrastructure 11g release 2 (11.2) Monthly Database Patch For Exadata (June 2014 - 11.2.0.4.8)

• Enable write-back flash cache on the storage server (cell)