tnsname.ora中的SOURCE_ROUTE，FAILOVER ，LOAD_BALANCE

转载

记住E是默认的

引用

Table 13-1 Address List Parameters
Parameter Description
SOURCE_ROUTE (Source Routing) When set to on, instructs Oracle Net to use each address in the order presented until the destination is reached. This parameter is required for reaching the destination using a specific route, that is, by specific machines. This parameter is used to enable connections to Oracle Connection Manager.

See Also: "Configuring Clients for Oracle Connection Manager" on page 13-6
FAILOVER (Connect-Time Failover) At connect time, instructs Oracle Net to fail over to a different listener if the first listener fails when set to on. The number of addresses in the list determines how many addresses are tried. When set to off, instructs Oracle Net to try one address.

Connect-time failover is turned on by default for multiple address lists (ADDRESS_LIST), connect descriptors (DESCRIPTION), and multiple connect descriptors (DESCRIPTION_LIST).

Important: Oracle Corporation recommends not setting the GLOBAL_DBNAME parameter in the SID_LIST_listener_name section of the listener.ora file. A statically configured global database name disables connect-time failover.
LOAD_BALANCE (Client Load Balancing) When set to on, instructs Oracle Net to progress through the list of protocol addresses in a random sequence, balancing the load on the various listeners. When set to off, instructs Oracle Net to try the addresses sequentially until one succeeds.

Client load balancing is turned on by default for multiple connect descriptors (DESCRIPTION_LIST).

引用

(A) Only the first address specified within the ADDRESS_LIST will be tried.
    If this address fails to connect then no other address will be attempted.

(B) It is assumed that a connection manger is being tried. The first address
    is tried. If a connection can be made then the CMAN will deal with the
    next hop. If the first address fails to connect then the connect attempt
    will fail, no other address will be tried.

(C) When LOAD_BALANCE is set only one address from the list of addresses will
    be selected at random. If this address fails to connect no other address
    will be selected. The 8.1.5 release seems to have a problem with true
    randomization , the first address in the ADDRESS_LIST will be selected much
    more often than the secondary address. For example, in a test of fifty
    connections the first address was selected on 42/50 occasions BUG 849436
    Problems with Load_balance Parameter.

(D) Same behavior as (B). In theory this set of parameters shouldn't be set.
    The Net8 Assiatant will never set this combination. SOURCE_ROUTE will
    override any other parameter.

(E) When FAILOVER is set each address will be tried, in the order specified
    within the ADDRESS_LIST, until a connection can be made. This is the same
    bahavior as you would expect from an ADDRESS_LIST in earlier versions of
    Net. Note that if no parameters are set then this is the default behavior
    for Net8i.

(F) Same behavior as (B). In theory this set of parameters shouldn't be set.
    The Net8 Assiatant will never set this combination. SOURCE_ROUTE will
    override any other parameter.

(G) When FAILOVER and LOAD_BALANCE have been set then Net8i will keep on
    randomly selecting addresses from the ADDRESS_LIST until either one address
    connects or all addresses have been tried. This is the old DESCRIPTION_LIST
    functionality.

(H) Same behavior as (B). In theory this set of parameters shouldn't be set.
    The Net8 Assiatant will never set this combination. SOURCE_ROUTE will
    override any other parameter.

The Net8 assistant can be used to configure these parameters. You cannot
however set any of these parameters explictly. Intead you have a JAVA dialog
box with a set of radio buttons:-

    . Try each address, in order, until one succeeds     (E)
    . Try each address, randomly, until one succeeds     (G)
    . Try one address, selected at random                (C)
    . Use each address in order until detination reached (B)
    . Use only the first address                         (A)

Most of them are obvious except for the SOURCE_ROUTE choice. There is also a
check box for whether or not the service name should be saved in 8.0 or 8i
format. If 8.0 is selected then only options (E) and (B) are enabled.

The most common used options will be:

    (E) - Standard FAILOVER (default behaviour)
    (G) - old DESCRIPTION_LIST behaviour
    (B) - Connection Manager routing

There does not appear to be much benefit in only selecting the first address
in the list to try (A), or in selecting one address to try (C).