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這篇文章主要介紹“sharding-jdbc路由的原理及應用”，在日常操作中，相信很多人在sharding-jdbc路由的原理及應用問題上存在疑惑，小編查閱了各式資料，整理出簡單好用的操作方法，希望對大家解答”sharding-jdbc路由的原理及應用”的疑惑有所幫助！接下來，請跟著小編一起來學習吧！
路由引擎主要分為兩大類：
分片路由（直接路由、標準路由、笛卡爾積路由）
廣播路由（全庫表路由、全庫路由、全實例路由、單播路由、阻斷路由）
具體路由類型含義參考官網路由引擎
https://shardingsphere.apache.org/document/current/cn/features/sharding/principle/route/
主要分析查詢路由
1.路由ParsingSQLRouter#route入口
@RequiredArgsConstructor
public final class ParsingSQLRouter implements ShardingRouter {
@Override
public SQLRouteResult route(final SQLStatement sqlStatement, final List<Object> parameters) {
//優化，處理條件占位符參數與真實數據、分頁、group by etc.
OptimizedStatement optimizedStatement = OptimizeEngineFactory.newInstance(shardingRule, shardingMetaData.getTable(), sqlStatement, parameters).optimize();
boolean needMergeShardingValues = isNeedMergeShardingValues(sqlStatement);
if (optimizedStatement instanceof ShardingWhereOptimizedStatement && needMergeShardingValues) {
checkSubqueryShardingValues(sqlStatement, ((ShardingWhereOptimizedStatement) optimizedStatement).getShardingConditions());
mergeShardingConditions(((ShardingWhereOptimizedStatement) optimizedStatement).getShardingConditions());
}
//路由入口
RoutingResult routingResult = RoutingEngineFactory.newInstance(shardingRule, shardingMetaData.getDataSource(), optimizedStatement).route();
if (needMergeShardingValues) {
Preconditions.checkState(1 == routingResult.getRoutingUnits().size(), "Must have one sharding with subquery.");
}
if (optimizedStatement instanceof ShardingInsertOptimizedStatement) {
setGeneratedValues((ShardingInsertOptimizedStatement) optimizedStatement);
}
SQLRouteResult result = new SQLRouteResult(optimizedStatement);
result.setRoutingResult(routingResult);
return result;
}
... ...
}2.路由工廠并路由RoutingEngineFactory#route
@NoArgsConstructor(access = AccessLevel.PRIVATE)
public final class RoutingEngineFactory {
/**
* Create new instance of routing engine.
*
* @param shardingRule sharding rule
* @param shardingDataSourceMetaData sharding data source meta data
* @param optimizedStatement optimized statement
* @return new instance of routing engine
*/
public static RoutingEngine newInstance(final ShardingRule shardingRule, final ShardingDataSourceMetaData shardingDataSourceMetaData, final OptimizedStatement optimizedStatement) {
SQLStatement sqlStatement = optimizedStatement.getSQLStatement();
Collection<String> tableNames = sqlStatement.getTables().getTableNames();
//全庫路由
if (sqlStatement instanceof TCLStatement) {
return new DatabaseBroadcastRoutingEngine(shardingRule);
}
//全庫表路由
if (sqlStatement instanceof DDLStatement) {
return new TableBroadcastRoutingEngine(shardingRule, optimizedStatement);
}
//阻斷路由
if (sqlStatement instanceof DALStatement) {
return getDALRoutingEngine(shardingRule, sqlStatement, tableNames);
}
//全實例路由
if (sqlStatement instanceof DCLStatement) {
return getDCLRoutingEngine(shardingRule, optimizedStatement, shardingDataSourceMetaData);
}
//默認庫路由
if (shardingRule.isAllInDefaultDataSource(tableNames)) {
return new DefaultDatabaseRoutingEngine(shardingRule, tableNames);
}
//全庫路由
if (shardingRule.isAllBroadcastTables(tableNames)) {
return sqlStatement instanceof SelectStatement ? new UnicastRoutingEngine(shardingRule, tableNames) : new DatabaseBroadcastRoutingEngine(shardingRule);
}
//單播路由
if (optimizedStatement instanceof ShardingWhereOptimizedStatement && ((ShardingWhereOptimizedStatement) optimizedStatement).getShardingConditions().isAlwaysFalse() || tableNames.isEmpty()) {
return new UnicastRoutingEngine(shardingRule, tableNames);
}
Preconditions.checkState(optimizedStatement instanceof ShardingWhereOptimizedStatement);
//分片路由
return getShardingRoutingEngine(shardingRule, (ShardingWhereOptimizedStatement) optimizedStatement, tableNames);
}
... ...
private static RoutingEngine getShardingRoutingEngine(final ShardingRule shardingRule, final ShardingWhereOptimizedStatement optimizedStatement, final Collection<String> tableNames) {
///根據解析出來邏輯表獲取分片表，如:SELECT i.* FROM t_order o, t_order_item i WHERE o.order_id = i.order_id and o.order_id = ?
//則shardingTableNames為t_order，t_order_item
Collection<String> shardingTableNames = shardingRule.getShardingLogicTableNames(tableNames);
//滿足以下兩個條件走標準路由，否則走復合路由
//1、是否只有一張分片表
//2、綁定的邏輯表（配置綁定表）是否包含所有分片表
if (1 == shardingTableNames.size() || shardingRule.isAllBindingTables(shardingTableNames)) {
//標準路由，獲取第一張表路由即可，參考官網案例說明
return new StandardRoutingEngine(shardingRule, shardingTableNames.iterator().next(), optimizedStatement);
}
// TODO config for cartesian set
//復合路由
return new ComplexRoutingEngine(shardingRule, tableNames, optimizedStatement);
}
}3.標準路由StandardRoutingEngine#route
標準路由場景
t_order和t_order_item是分庫分表并且是綁定表；如第二步55行判斷shardingTableNames.size()=1或者shardingTableNames都是綁定表時，這時會走標準路由
@RequiredArgsConstructor
public final class StandardRoutingEngine implements RoutingEngine {
//分庫分表規則
private final ShardingRule shardingRule;
//邏輯表 t_order
private final String logicTableName;
//sql解析并優化后的結果
private final ShardingWhereOptimizedStatement optimizedStatement;
@Override
public RoutingResult route() {
//insert、update、delete判斷表是否是單表
if (isDMLForModify(optimizedStatement.getSQLStatement()) && !optimizedStatement.getSQLStatement().getTables().isSingleTable()) {
throw new SQLParsingException("Cannot support Multiple-Table for '%s'.", optimizedStatement.getSQLStatement());
}
//路由數據節點、封裝路由結果
return generateRoutingResult(getDataNodes(shardingRule.getTableRule(logicTableName)));
}
... ...
private RoutingResult generateRoutingResult(final Collection<DataNode> routedDataNodes) {
RoutingResult result = new RoutingResult();
//根據數據節點封裝路由單元、表單元
for (DataNode each : routedDataNodes) {
//路由單元 demo_ds_0
RoutingUnit routingUnit = new RoutingUnit(each.getDataSourceName());
//表單元 邏輯表:真實表 t_order:t_order_0
routingUnit.getTableUnits().add(new TableUnit(logicTableName, each.getTableName()));
result.getRoutingUnits().add(routingUnit);
}
return result;
}
private Collection<DataNode> getDataNodes(final TableRule tableRule) {
//判斷database、table分片策略同時是Hint(直接路由)
if (shardingRule.isRoutingByHint(tableRule)) {
return routeByHint(tableRule);
}
//database、table分片策略都不是Hint
if (isRoutingByShardingConditions(tableRule)) {
//根據分片條件、策略路由到對應的database、table，同對分片鍵判斷
return routeByShardingConditions(tableRule);
}
//database或table分片策略有一個是Hint
return routeByMixedConditions(tableRule);
}
... ...
}4.復合路由CartesianRoutingEngine#route
復雜路由場景
t_order和t_order_item是分庫分表并且是綁定表；新增一個t_user分庫分表，這時第二步的55行，shardingTableNames.size()=3，且t_user未配置成綁定表，這時會走復合路由
@RequiredArgsConstructor
public final class ComplexRoutingEngine implements RoutingEngine {
//分庫分表規則
private final ShardingRule shardingRule;
//邏輯表t_order、t_order_item
private final Collection<String> logicTables;
//sql解析并優化后的結果
private final ShardingWhereOptimizedStatement optimizedStatement;
@Override
public RoutingResult route() {
Collection<RoutingResult> result = new ArrayList<>(logicTables.size());
Collection<String> bindingTableNames = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
//遍歷邏輯表
for (String each : logicTables) {
Optional<TableRule> tableRule = shardingRule.findTableRule(each);
//表是否配置了分庫分表規則
if (tableRule.isPresent()) {
// 如果綁定關系表已經處理過，那么不需要再處理，如t_order處理過，由于t_order_item與其是綁定關系，那么不需要再處理；
if (!bindingTableNames.contains(each)) {
//構建標準路由并路由
result.add(new StandardRoutingEngine(shardingRule, tableRule.get().getLogicTable(), optimizedStatement).route());
}
//根據邏輯表查找對應的所有綁定表，如根據t_order就能查詢到t_order、t_order_item，因為t_order和t_order_item是綁定表
Optional<BindingTableRule> bindingTableRule = shardingRule.findBindingTableRule(each);
if (bindingTableRule.isPresent()) {
//添加綁定表
bindingTableNames.addAll(Lists.transform(bindingTableRule.get().getTableRules(), new Function<TableRule, String>() {
@Override
public String apply(final TableRule input) {
return input.getLogicTable();
}
}));
}
}
}
if (result.isEmpty()) {
throw new ShardingException("Cannot find table rule and default data source with logic tables: '%s'", logicTables);
}
if (1 == result.size()) {
return result.iterator().next();
}
//笛卡爾積路由
return new CartesianRoutingEngine(result).route();
}
}5.笛卡爾積路由
笛卡爾積路由場景
笛卡爾路由是最復雜的情況，它無法根據綁定表的關系定位分片規則，因此非綁定表之間的關聯查詢需要拆解為笛卡爾積組合執行。如上面事例新增的t_user分庫分表，t_user和t_order未配置綁定表關系，如下SQL就需要走笛卡爾積路由
SELECT * FROM t_user u JOIN t_order o ON u.user_id = o.user_id AND u.user_id in(1 , 2)
@RequiredArgsConstructor
public final class CartesianRoutingEngine implements RoutingEngine {
private final Collection<RoutingResult> routingResults;
@Override
public RoutingResult route() {
RoutingResult result = new RoutingResult();
//獲取數據源對應的邏輯表集合
for (Entry<String, Set<String>> entry : getDataSourceLogicTablesMap().entrySet()) {
//通過數據源名稱和邏輯表的名稱獲取實際的表組，即[["t_user_0","t_user_1"],["t_order_0", "t_order_1]]
List<Set<String>> actualTableGroups = getActualTableGroups(entry.getKey(), entry.getValue());
//把邏輯表名封裝成TableUnit表單元
//TableUnit包含數據源名稱、邏輯表名、實際表名（通過這三個屬性可以確定最終訪問的表）
List<Set<TableUnit>> routingTableGroups = toRoutingTableGroups(entry.getKey(), actualTableGroups);
//封裝RoutingUnit路由單元
//cartesianProduct計算笛卡爾積
result.getRoutingUnits().addAll(getRoutingUnits(entry.getKey(), Sets.cartesianProduct(routingTableGroups)));
}
return result;
}
private Map<String, Set<String>> getDataSourceLogicTablesMap() {
//獲取數據源的交集，如t_user邏輯表路由到數據源demo_ds_0，而t_order表路由到數據源ds_demo_0和demo_ds_1，數據源交集就是demo_ds_0
//事例SELECT * FROM t_user_0 u JOIN t_order_0 o ON u.user_id = o.user_id WHERE u.user_id in(1, 2); t_user和t_order不是綁定表關系
//笛卡爾路由是最復雜的情況，它無法根據綁定表的關系定位分片規則，因此非綁定表之間的關聯查詢需要拆解為笛卡爾積組合執行
Collection<String> intersectionDataSources = getIntersectionDataSources();
Map<String, Set<String>> result = new HashMap<>(routingResults.size());
//遍歷標準路由后的結果集
for (RoutingResult each : routingResults) {
//通過數據源的名稱獲取數據源和邏輯表之間的映射關系
for (Entry<String, Set<String>> entry : each.getDataSourceLogicTablesMap(intersectionDataSources).entrySet()) {
if (result.containsKey(entry.getKey())) {
result.get(entry.getKey()).addAll(entry.getValue());
} else {
result.put(entry.getKey(), entry.getValue());
}
}
}
// 返回數據源-邏輯表集合組成的Map，這里就是{"demo_ds_0":["t_user", "t_order"]}
return result;
}
private Collection<String> getIntersectionDataSources() {
Collection<String> result = new HashSet<>();
for (RoutingResult each : routingResults) {
if (result.isEmpty()) {
result.addAll(each.getDataSourceNames());
}
//交集
result.retainAll(each.getDataSourceNames());
}
return result;
}
... ...
}笛卡爾積結果如下：
6.直接路由
直接路由場景
滿足直接路由的條件相對苛刻，它需要通過Hint（使用HintAPI直接指定路由至庫表）方式分片，并且是只分庫不分表的前提下，則可以避免SQL解析和之后的結果歸并
假如路由算法為value % 2，當一個邏輯庫t_order對應2個真實庫t_order_0和t_order_1時，路由后SQL將在t_order_1上執行。下方是使用API的代碼樣例:
String sql = "SELECT * FROM t_order";
try (
//獲取Hint實例
HintManager hintManager = HintManager.getInstance();
Connection conn = dataSource.getConnection();
PreparedStatement pstmt = conn.prepareStatement(sql)) {
//設置數據源分片個數
hintManager.setDatabaseShardingValue(3);
try (ResultSet rs = pstmt.executeQuery()) {
while (rs.next()) {
//...
}
}
}@RequiredArgsConstructor
public final class DatabaseHintRoutingEngine implements RoutingEngine {
//數據源集群
private final Collection<String> dataSourceNames;
//Hint數據分片策略
private final HintShardingStrategy databaseShardingStrategy;
@Override
public RoutingResult route() {
//獲取當前線程數據源分片
Collection<Comparable<?>> shardingValues = HintManager.getDatabaseShardingValues();
Preconditions.checkState(!shardingValues.isEmpty());
Collection<String> routingDataSources;
//根據分片策略路由
routingDataSources = databaseShardingStrategy.doSharding(dataSourceNames, Collections.<RouteValue>singletonList(new ListRouteValue<>("", "", shardingValues)));
Preconditions.checkState(!routingDataSources.isEmpty(), "no database route info");
RoutingResult result = new RoutingResult();
//封裝路由單元
for (String each : routingDataSources) {
result.getRoutingUnits().add(new RoutingUnit(each));
}
return result;
}
}到此，關于“sharding-jdbc路由的原理及應用”的學習就結束了，希望能夠解決大家的疑惑。理論與實踐的搭配能更好的幫助大家學習，快去試試吧！若想繼續學習更多相關知識，請繼續關注億速云網站，小編會繼續努力為大家帶來更多實用的文章！
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