Tuning the Cluster Interconnect - Expert Oracle RAC Performance Diagnostics and Tuning

Database Reference

In-Depth Information

[oracle@prddb1]$ /sbin/ifconfig -a

eth1 Link encap:Ethernet HWaddr 00:0C:29:3A:F1:6E

inet addr:172.35.1.11 Bcast:172.35.1.255 Mask:255.255.255.0

inet6 addr: fe80::20c:29ff:fe3a:f16e/64 Scope:Link

UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

RX packets:42232 errors:0 dropped:0 overruns:0 frame:0

TX packets:11 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:3483899 (3.3 MiB) TX bytes:678 (678.0 b)

Base address:0x2440 Memory:d8960000-d8980000

The value of the netdev_max_backlog parameter can be viewed from the following:

[oracle@prddb1]$ cat /proc/sys/net/core/netdev_max_backlog 300

These values can be manually defined using the ifconfig command on Linux and Unix systems. For example,

the following command will reset the txqueuelen to 2000:

/sbin/ifconfig eth1 txqueuelen 2000

Similarly, the receive queue size can be increased by setting the following parameter file:

/proc/sys/net/core/netdev_max_backlog = 2000 in the /etc/sysctl.conf

Normally, the transmit (send) and the receive queue lengths should be set identical to avoid send or receive bottlenecks.

Transport Unit Size

Ethernet traffic moves in units called frames . Ethernet's variable frame size of 46-1,500 bytes is the transfer unit

between the all Ethernet participants, such as the hosts and switches. The upper bound, in this case 1,500, is called

Maximum Transmission Unit (MTU) and is the largest packet a network device transmits. When an application

sends a message greater than 1,500 bytes (MTU), it is fragmented (broken into smaller frames) into 1,500-byte

frames or smaller; or as a worst case, it's dropped. As illustrated in the ifconfig output following, historically,

Ethernet has a maximum frame size of 1,500 bytes; 3 so most devices use 1,500 as their default MTU. To maintain

backward compatibility, the “standard” GigE also uses 1,500-byte frames. This is maintained so a packet to/from any

combination of 10/100/1000/10000 Mbps Ethernet devices can be handled without any layer two fragmentation or

reassembly. An Ethernet packet larger than 1,500 bytes is called a jumbo frame .