Database Reference
In-Depth Information
You can also use the TCP_KEEPALIVE_THRESHOLD socket option on individual appli-
cations to override the default interval so that each application can have its own
interval on each socket. The option value is an unsigned integer in milliseconds. See
also tcp(7P).
The Solaris manual goes on to state that the commitment level for the parameter is
unstable and that it should not be changed. To the best of my knowledge,
tcp_keepalive_
threshold
is not implemented in ORACLE DBMS software. Instead of modifying keep-alive
settings, the Solaris documentation recommends changing re-transmit time-outs (
tcp_
rexmit_interval_max
and
tcp_ip_abort_interval
).
A while back, my own testing with Oracle8
i
confirmed that
ENABLE=BROKEN
is functional
and useful given that
tcp_keepalive_interval
and
tcp_keepalive_abort_interval
are adjusted as
needed. Tracing with
truss
showed that it is still implemented in Oracle10
g
. Keep in mind that
an appropriate test for all of these TCP/IP settings consists of either pulling the network cable
(and keeping it pulled), switching off the server, or any other method of bringing down the
operating system (Stop+A on Solaris), such that it does not stand a chance of sending a message to
a remote system to indicate that sockets should be closed. Such a test should be performed on
any RAC cluster before it moves into production.
Before I move off topic any further, let me explain why
ENABLE=BROKEN
should be considered an
outdated feature. With Oracle10
g
Clusterware and virtual IP addresses the IP address that went
down on a failed host is brought back online on a surviving node. Re-transmits by the client
should then be redirected to a surviving node and fail, since it knows nothing about the sockets
that were open on the failed node. As part of virtual IP address (VIP) failover, Oracle Cluster-
ware flushes the address resolution protocol (ARP) cache, which translates between IP addresses
and MAC (medium access control) addresses of ethernet adapters. This is undocumented, but
is essential in accomplishing successful reconnects by database clients, which must become
aware of the new mapping between IP address and MAC address. On Linux, the ARP cache is
flushed by executing the command
/sbin/arping -q -U -c 3 -I
adapter
ip_address
in the
script
$ORA_CRS_HOME/bin/racgvip
. The mapping between MAC and IP addresses may be displayed
with the command
arp
-a
on UNIX as well as Windows.
Additional information on the subject of TCP/IP and failover is in Metalink note 249213.1.
According to the note, Sun Microsystems suggests setting
tcp_keepalive_interval
,
tcp_ip_
abort_cinterval
(prevents connect attempts to the failed node from waiting up to three minutes),
and
tcp_ip_abort_interval
(by default, a connection is closed after not receiving an acknowl-
edgment for eight minutes). Unfortunately, the Metalink note does not state that
tcp_keepalive_
interval
is ignored, unless
SO_KEEPALIVE
is set on the socket, which in turn requires
ENABLE=BROKEN
.
I recommend adjusting
tcp_ip_abort_cinterval
to prevent connections initiated before
the virtual IP address has come back online on a surviving node from locking up for up to three
minutes. I also suggest reducing the values of the parameters
tcp_ip_abort_interval
and
tcp_
rexmit_interval_max
to 45 seconds (default: 8 minutes) and 30 seconds (default: 3 minutes)
respectively. These parameters must be changed on the database client machine—remember,
