doris Aggregate查询rollup explain 查询 使用expalin作为前缀可以查看当前sql语句的执行效率,以便于优化sql语句。explain的参数主要有十个分别为:id、select_type、table、type、possible_keys、key、key_len、ref、rows、Extra。 1. explain的作用: 例如: 1、id:id的值越大则代表越先执行。 2、select_type:常见的...
rollup函数使用sort耗时长,总耗时达到50s(即17号-20号算子的总耗时),(并行度32的情况下),20号算子Vector sort达24s,19号算子Vector Sore Aggregate达9s,18号算子做重分布达10s,17号算子hashagg达到8s。因此需要考虑对rollup类的分析函数考虑使用其它方式进行优化,比如用hashagg替代sortagg,避免大数据量排序性能降低。
the MySQL optimizer considers many techniques to efficiently performthe lookups involved in an SQL query. A query on a huge table can be performedwithout reading all the rows; a join involving several tables can be performedwithout comparing every combination of rows. The set of operations...
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if (!ji || ji->created_functions == 0) return; /* calculate total time */ INSTR_TIME_SET_ZERO(total_time); INSTR_TIME_ADD(total_time, ji->generation_counter); INSTR_TIME_ADD(total_time, ji->inlining_counter); INSTR_TIME_ADD(total_time, ji->optimization_counter); INSTR_TIME_ADD(...
Your goals areto recognize the aspects of the EXPLAIN plan that indicate a query is optimizedwell, and to learn the SQL syntax and indexing techniques to improve the planif you see some inefficient operations. 查看执行计划示例: mysql>explain select * from user where User='root'; ...
GroupByOperator (AGGREGATE): describes the logic of aggregate operations. This operator is displayed if an aggregate function is used in a query statement. The content of the aggregate function is displayed in the execution results of the EXPLAIN statement. ReduceSinkOperator (RS): describes the ...
AggregateaggrOperator/step for scalar aggregate functions. HashAggregateaggrOperator/step for grouped aggregate functions. Can operate from disk by virtue of hash table spilling to disk. GroupAggregateaggrOperator sometimes chosen for grouped aggregate queries if the Amazon Redshift configuration setting for...
For example, if a hash aggregate operator is used in the first step of a query plan, full data of downstream operators is required to create a hash table for an aggregate operation. For common queries with filter conditions, data is calculated and returned in real time. In this scenario, ...
Today, I'll write about four more userful functions:FIRST_VALUE,LAST_VALUE,LEADandLAG. These functions also do not have aggregate analogs. FIRST VALUE(column)returns the value of column from the first row of the grouping set. LAST_VALUE(column)returns the value of column from the last row...