测试连接负载均衡策略

创建路由规则后，您应当测试它们以验证它们是否按预期方式执行。测试规则的最佳方法是使用 IP 地址调用 DESCRIBE_LOAD_BALANCE_DECISION 函数。此函数评估路由规则并报告 Vertica 如何从 IP 地址路由客户端连接。它使用的逻辑与 Vertica 用来处理客户端连接的逻辑相同，因此结果反映了您将从客户端连接中看到的实际连接负载均衡结果。它还反映了 Vertica 群集的当前状态，因此它不会将连接重定向到已关闭的节点。

以下示例演示了如何测试一组规则。一条规则处理从 192.168.1.0 到 192.168.1.255 范围内的所有连接，而另一条规则处理源自 192 子网的所有连接。第三个调用演示了当没有规则适用于您提供的 IP 地址时会发生什么。

=> 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)

DESCRIBE_LOAD_BALANCE_DECISION 函数还考虑了群集范围的经典负载均衡设置：

=>  SELECT SET_LOAD_BALANCE_POLICY('ROUNDROBIN');
                            SET_LOAD_BALANCE_POLICY
--------------------------------------------------------------------------------
 Successfully changed the client initiator load balancing policy to: roundrobin
(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: Success. Load balance redirect to: [10.20.100.247]
port [5433]

(1 row)

此函数还可以帮助您调试在使用负载均衡策略后发现的连接问题。例如，如果您注意到一个节点正在处理大量客户端连接，您可以对照您的策略测试客户端 IP 地址，以了解连接不平衡的原因。