If there is a fresh query and its hash code does not exist in shared pool then that query has to pass through from the additional steps known as hard parsing otherwise if hash code exists then query does not passes through additional steps. It just passes directly to execution engine (refer...
执行计划超出了并行执行(parallel execution)的界限 * parallel execution 利用多处理器提高执行效率 统计数据过期或者发生了改变 1.4预估的和实际的执行计划 如前所述,有两种不同的执行计划,第一个是由优化器产生的预估的执行计划(Estimated execution plan),操作符和步骤被贴了Logical标签,代表了优化器的观点,另一个...
Object parameter) throws SQLException; /** * 查询,带 ResultHandler + CacheKey + BoundSql */ <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler
1private<E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)throwsSQLException {2List<E>list;3localCache.putObject(key, EXECUTION_PLACEHOLDER);4try{ //在子类中实现的 doQuery 查询出来结果放入一级缓存5...
(st.text) ELSE qs.statement_end_offset END - qs.statement_start_offset)/2) + 1) N'执行语句' ,creation_time N'语句编译时间' ,last_execution_time N'上次执行时间' FROM sys.dm_exec_query_stats AS qs CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) st WHERE SUBSTRING(st.text, (qs....
而Query和QuerySpecification由RelationPlanner委托QueryPlanner来分析。 代码语言:javascript 复制 privateRelationPlancreateRelationPlan(Analysis analysis,Query query){returnnewRelationPlanner(analysis,symbolAllocator,idAllocator,buildLambdaDeclarationToSymbolMap(analysis,symbolAllocator),metadata,session).process(query,null...
def executePlan(plan: LogicalPlan): QueryExecution = createQueryExecution(plan) 1. 第九步:createQueryExecution(plan)创建QueryExecution /** * QueryExecution是Spark用来执行关系型查询的主要工作流。 * 它是被设计用来为开发人员提供更方便的对查询执行中间阶段的访问。 * QueryExecution中最重要的是成员变量,...
For this, access to the actual execution plan is important.While query completion is a prerequisite for the availability of an actual query plan, live query statistics can provide real-time insights into the query execution process as the data flows from one query plan operator to...
They can trust that the query optimizer will build an efficient execution plan for the state of the database every time the statement is run. Processing a SELECT Statement The basic steps that SQL Server uses to process a single SELECT statement include the following: The parser scans the ...
//第一次,没有缓存,所以会调用queryFromDatabase方法来执行查询。 privateListqueryFromDatabase(...) throws SQLException { Listlist; localCache.putObject(key, EXECUTION_PLACEHOLDER); try { // 查询 list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql); ...