使用子群集管理工作负载
默认情况下，查询仅限于在包含启动程序节点（客户端连接到的节点）的子群集中的节点上执行。此示例演示了如何在连接到群集的节点 4 时执行查询的解释计划。节点 4 是包含节点 4 到 6 的子群集的一部分。您可以看到只有子群集中的节点才会参与查询：
=> EXPLAIN SELECT customer_name, customer_state FROM customer_dimension LIMIT 10;
QUERY PLAN
--------------------------------------------------------------------------------
QUERY PLAN DESCRIPTION:
------------------------------
EXPLAIN SELECT customer_name, customer_state FROM customer_dimension LIMIT 10;
Access Path:
+-SELECT LIMIT 10 [Cost: 442, Rows: 10 (NO STATISTICS)] (PATH ID: 0)
| Output Only: 10 tuples
| Execute on: Query Initiator
| +---> STORAGE ACCESS for customer_dimension [Cost: 442, Rows: 10K (NO
STATISTICS)] (PATH ID: 1)
| | Projection: public.customer_dimension_b0
| | Materialize: customer_dimension.customer_name,
customer_dimension.customer_state
| | Output Only: 10 tuples
| | Execute on: v_verticadb_node0004, v_verticadb_node0005,
v_verticadb_node0006
. . .
在 Eon 模式下，您可以覆盖内置全局资源池的 MEMORYSIZE、 MAXMEMORYSIZE 和 MAXQUERYMEMORYSIZE 设置以微调子群集中的工作负载。有关详细信息，请参阅管理 Eon 模式数据库中的工作负载资源。
子群集无法运行查询时发生的情况
为了处理查询，每个子群集的节点必须完全覆盖数据库中的所有分片。如果节点没有完全覆盖（在节点出现故障时可能会发生这种情况），子群集将无法再处理查询。此状态不会导致子群集关闭。不过，如果您尝试在此状态下对子群集运行某个查询，则会收到错误消息，告知您没有足够的节点可用于完成该查询。
=> SELECT node_name, node_state FROM nodes
WHERE subcluster_name = 'analytics_cluster';
node_name | node_state
----------------------+------------
v_verticadb_node0004 | DOWN
v_verticadb_node0005 | UP
v_verticadb_node0006 | DOWN
(3 rows)
=> SELECT * FROM online_sales.online_sales_fact;
ERROR 9099: Cannot find participating nodes to run the query
发生故障的节点已恢复且子群集具有百分之百的分片覆盖率后，它将能够处理查询。
控制查询的运行位置
您可以通过控制客户端将连接到的子群集来控制特定类型的查询的运行位置。强制执行限制的最佳方式是创建一组连接负载均衡策略，将客户端从特定 IP 地址范围引导至正确子群集中的客户端。
例如，假设您有以下数据库，其中包含两个子群集：一个用于执行数据加载，一个用于执行分析。
数据加载任务来自 IP 10.20.0.0/16 地址范围内的一组 ETL 系统。分析任务可能来自任何其他 IP 地址。在这种情况下，您可以创建一组连接负载均衡策略，以确保 ETL 系统连接到数据加载子群集，而所有其他连接都进入分析子群集。
=> SELECT node_name,node_address,node_address_family,subcluster_name
FROM v_catalog.nodes;
node_name | node_address | node_address_family | subcluster_name
----------------------+--------------+---------------------+--------------------
v_verticadb_node0001 | 10.11.12.10 | ipv4 | load_subcluster
v_verticadb_node0002 | 10.11.12.20 | ipv4 | load_subcluster
v_verticadb_node0003 | 10.11.12.30 | ipv4 | load_subcluster
v_verticadb_node0004 | 10.11.12.40 | ipv4 | analytics_subcluster
v_verticadb_node0005 | 10.11.12.50 | ipv4 | analytics_subcluster
v_verticadb_node0006 | 10.11.12.60 | ipv4 | analytics_subcluster
(6 rows)
=> CREATE NETWORK ADDRESS node01 ON v_verticadb_node0001 WITH '10.11.12.10';
CREATE NETWORK ADDRESS
=> CREATE NETWORK ADDRESS node02 ON v_verticadb_node0002 WITH '10.11.12.20';
CREATE NETWORK ADDRESS
=> CREATE NETWORK ADDRESS node03 ON v_verticadb_node0003 WITH '10.11.12.30';
CREATE NETWORK ADDRESS
=> CREATE NETWORK ADDRESS node04 ON v_verticadb_node0004 WITH '10.11.12.40';
CREATE NETWORK ADDRESS
=> CREATE NETWORK ADDRESS node05 ON v_verticadb_node0005 WITH '10.11.12.50';
CREATE NETWORK ADDRESS
=> CREATE NETWORK ADDRESS node06 ON v_verticadb_node0006 WITH '10.11.12.60';
CREATE NETWORK ADDRESS
=> CREATE LOAD BALANCE GROUP load_subcluster WITH SUBCLUSTER load_subcluster
FILTER '0.0.0.0/0';
CREATE LOAD BALANCE GROUP
=> CREATE LOAD BALANCE GROUP analytics_subcluster WITH SUBCLUSTER
analytics_subcluster FILTER '0.0.0.0/0';
CREATE LOAD BALANCE GROUP
=> CREATE ROUTING RULE etl_systems ROUTE '10.20.0.0/16' TO load_subcluster;
CREATE ROUTING RULE
=> CREATE ROUTING RULE analytic_clients ROUTE '0.0.0.0/0' TO analytics_subcluster;
CREATE ROUTING RULE
创建负载均衡策略后，您可以使用 DESCRIBE_LOAD_BALANCE_DECISION 函数对其进行测试。
=> SELECT describe_load_balance_decision('192.168.1.1');
describe_load_balance_decision
--------------------------------
Describing load balance decision for address [192.168.1.1]
Load balance cache internal version id (node-local): [1]
Considered rule [etl_systems] source ip filter [10.20.0.0/16]...
input address does not match source ip filter for this rule.
Considered rule [analytic_clients] source ip filter [0.0.0.0/0]...
input address matches this rule
Matched to load balance group [analytics_cluster] the group has
policy [ROUNDROBIN] number of addresses [3]
(0) LB Address: [10.11.12.181]:5433
(1) LB Address: [10.11.12.205]:5433
(2) LB Address: [10.11.12.192]:5433
Chose address at position [1]
Routing table decision: Success. Load balance redirect to: [10.11.12.205]
port [5433]
(1 row)
=> SELECT describe_load_balance_decision('10.20.1.1');
describe_load_balance_decision
--------------------------------
Describing load balance decision for address [10.20.1.1]
Load balance cache internal version id (node-local): [1]
Considered rule [etl_systems] source ip filter [10.20.0.0/16]...
input address matches this rule
Matched to load balance group [default_cluster] the group has policy
[ROUNDROBIN] number of addresses [3]
(0) LB Address: [10.11.12.10]:5433
(1) LB Address: [10.11.12.20]:5433
(2) LB Address: [10.11.12.30]:5433
Chose address at position [1]
Routing table decision: Success. Load balance redirect to: [10.11.12.20]
port [5433]
(1 row)
通常，使用这些策略时，ETL 系统运行的所有查询都将在加载子群集上运行。所有其他查询将在分析子群集上运行。在某些情况下（尤其是在子群集发生故障或排空的情况下），客户端可能会连接到另一个子群集中的节点。为此，客户端应始终验证它们是否已连接到正确的子群集。有关负载均衡策略的详细信息，请参阅连接负载均衡策略。