DESCRIBE_LOAD_BALANCE_DECISION

Evaluates if any load balancing routing rules apply to a given IP address and This function is useful when you are evaluating connection load balancing policies you have created, to ensure they work the way you expect them to.

Evaluates if any load balancing routing rules apply to a given IP address and describes how the client connection would be handled. This function is useful when you are evaluating connection load balancing policies you have created, to ensure they work the way you expect them to.

You pass this function an IP address of a client connection, and it uses the load balancing routing rules to determine how the connection will be handled. The logic this function uses is the same logic used when Vertica load balances client connections, including determining which nodes are available to handle the client connection.

This function assumes the client connection has opted into being load balanced. If actual clients have not opted into load balancing, the connections will not be redirected. See Load balancing in ADO.NET, Load balancing in JDBC, and Load balancing in ODBC, for information on enabling load balancing on the client. For vsql, use the -C command-line option to enable load balancing.

This is a meta-function. You must call meta-functions in a top-level SELECT statement.

Behavior type

Volatile

Syntax

DESCRIBE_LOAD_BALANCE_DECISION('ip_address')

Arguments

'ip_address': An IP address of a client connection to be tested against the load balancing rules. This can be either an IPv4 or IPv6 address.

Return value

A step-by-step description of how the load balancing rules are being evaluated, including the final decision of which node in the database has been chosen to service the connection.

Privileges

None.

Examples

The following example demonstrates calling DESCRIBE_LOAD_BALANCE_DECISION with three different IP addresses, two of which are handled by different routing rules, and one which is not handled by any rule.

=> SELECT describe_load_balance_decision('192.168.1.25');
                        describe_load_balance_decision
--------------------------------------------------------------------------------
 Describing load balance decision for address [192.168.1.25]
Load balance cache internal version id (node-local): [2]
Considered rule [etl_rule] source ip filter [10.20.100.0/24]... input address
does not match source ip filter for this rule.
Considered rule [internal_clients] source ip filter [192.168.1.0/24]... input
address matches this rule
Matched to load balance group [group_1] the group has policy [ROUNDROBIN]
number of addresses [2]
(0) LB Address: [10.20.100.247]:5433
(1) LB Address: [10.20.100.248]:5433
Chose address at position [1]
Routing table decision: Success. Load balance redirect to: [10.20.100.248] port [5433]

(1 row)

=> SELECT describe_load_balance_decision('192.168.2.25');
                        describe_load_balance_decision
--------------------------------------------------------------------------------
 Describing load balance decision for address [192.168.2.25]
Load balance cache internal version id (node-local): [2]
Considered rule [etl_rule] source ip filter [10.20.100.0/24]... input address
does not match source ip filter for this rule.
Considered rule [internal_clients] source ip filter [192.168.1.0/24]... input
address does not match source ip filter for this rule.
Considered rule [subnet_192] source ip filter [192.0.0.0/8]... input address
matches this rule
Matched to load balance group [group_all] the group has policy [ROUNDROBIN]
number of addresses [3]
(0) LB Address: [10.20.100.247]:5433
(1) LB Address: [10.20.100.248]:5433
(2) LB Address: [10.20.100.249]:5433
Chose address at position [1]
Routing table decision: Success. Load balance redirect to: [10.20.100.248] port [5433]

(1 row)

=> SELECT describe_load_balance_decision('1.2.3.4');
                         describe_load_balance_decision
--------------------------------------------------------------------------------
 Describing load balance decision for address [1.2.3.4]
Load balance cache internal version id (node-local): [2]
Considered rule [etl_rule] source ip filter [10.20.100.0/24]... input address
does not match source ip filter for this rule.
Considered rule [internal_clients] source ip filter [192.168.1.0/24]... input
address does not match source ip filter for this rule.
Considered rule [subnet_192] source ip filter [192.0.0.0/8]... input address
does not match source ip filter for this rule.
Routing table decision: No matching routing rules: input address does not match
any routing rule source filters. Details: [Tried some rules but no matching]
No rules matched. Falling back to classic load balancing.
Classic load balance decision: Classic load balancing considered, but either
the policy was NONE or no target was available. Details: [NONE or invalid]

(1 row)

The following example demonstrates calling DESCRIBE_LOAD_BALANCE_DECISION repeatedly with the same IP address. You can see that the load balance group's ROUNDROBIN load balance policy has it switch between the two nodes in the load balance group:

=> SELECT describe_load_balance_decision('192.168.1.25');
                       describe_load_balance_decision
--------------------------------------------------------------------------------
 Describing load balance decision for address [192.168.1.25]
Load balance cache internal version id (node-local): [1]
Considered rule [etl_rule] source ip filter [10.20.100.0/24]... input address
does not match source ip filter for this rule.
Considered rule [internal_clients] source ip filter [192.168.1.0/24]... input
address matches this rule
Matched to load balance group [group_1] the group has policy [ROUNDROBIN]
number of addresses [2]
(0) LB Address: [10.20.100.247]:5433
(1) LB Address: [10.20.100.248]:5433
Chose address at position [1]
Routing table decision: Success. Load balance redirect to: [10.20.100.248]
port [5433]

(1 row)

=> SELECT describe_load_balance_decision('192.168.1.25');
                        describe_load_balance_decision
--------------------------------------------------------------------------------
 Describing load balance decision for address [192.168.1.25]
Load balance cache internal version id (node-local): [1]
Considered rule [etl_rule] source ip filter [10.20.100.0/24]... input address
does not match source ip filter for this rule.
Considered rule [internal_clients] source ip filter [192.168.1.0/24]... input
address matches this rule
Matched to load balance group [group_1] the group has policy [ROUNDROBIN]
number of addresses [2]
(0) LB Address: [10.20.100.247]:5433
(1) LB Address: [10.20.100.248]:5433
Chose address at position [0]
Routing table decision: Success. Load balance redirect to: [10.20.100.247]
port [5433]

(1 row)

=> SELECT describe_load_balance_decision('192.168.1.25');
                         describe_load_balance_decision
--------------------------------------------------------------------------------
 Describing load balance decision for address [192.168.1.25]
Load balance cache internal version id (node-local): [1]
Considered rule [etl_rule] source ip filter [10.20.100.0/24]... input address
does not match source ip filter for this rule.
Considered rule [internal_clients] source ip filter [192.168.1.0/24]... input
address matches this rule
Matched to load balance group [group_1] the group has policy [ROUNDROBIN]
number of addresses [2]
(0) LB Address: [10.20.100.247]:5433
(1) LB Address: [10.20.100.248]:5433
Chose address at position [1]
Routing table decision: Success. Load balance redirect to: [10.20.100.248]
port [5433]

(1 row)