This is how many blocks you processed in "consistent read" mode. This will include counts of blocks read from the rollback segment in order to roll back a block. This is the mode you read blocks in with a SELECT, for example. Also, when you do a searched UPDATE/DELETE, you read the...
This is how many blocks you processed in "consistent read" mode. This will include counts of blocks read from the rollback segment in order to roll back a block. This is the mode you read blocks in with a SELECT, for example. Also, when you do a searched UPDATE/DELETE, you read the...
使用了连接缓存:Block Nested Loop,连接算法是块嵌套循环连接;Batched Key Access,连接算法是批量索引连接 Impossible where 该WHERE子句始终为false,不能选择任何行。 Select tables optimized away 在没有GROUP BY子句的情况下,基于索引优化MIN/MAX操作,或者对于MyISAM存储引擎优化COUNT(*)操作,不必等到执行阶段再进行...
Nested LoopnloopLeast optimal join; mainly used for cross-joins (Cartesian products; without a join condition) and some inequality joins. Hash JoinhjoinAlso used for inner joins and left and right outer joins and typically faster than a nested loop join. Hash Join reads the outer table, hash...
derivedN: The row refers to the derived table result for the row with an id value of N. A derived table may result, for example, from a subquery in the FROM clause. subqueryN: The row refers to the result of a materialized subquery for the row with an id value of N. ...
(cost=103382.56 rows=1029632) -> Nested loop inner join (cost=409.36 rows=4022) -> Filter: (nation.N_NAME = 'IRAN') (cost=2.29 rows=3) -> Table scan on nation (cost=2.29 rows=25) -> Parallel index lookup on supplier using SUPPLIER_FK1 (S_NATIONKEY=nation.N_NATIONKEY), with ...
Figure 18: Example plan output using NESTED LOOP Sort Merge joins – Sort merge joins are useful when the join condition between two tables is an in-equality condition such as, <, <=, >, or >=. Sort merge joins can perform better than nested loop joins for large data sets. The join...
EXPLAIN returnsa row of information for each table used in the SELECT statement. It lists thetables in the output in the order that MySQL would read them while processingthe statement. MySQL resolves all joins using a nested-loop join method. Thismeans that MySQL reads a row from the first...
We’ll start at the end with the number of loops. The number of loops for this filtering iterator is 2. What does that mean? To understand this number, we have to look what’s above the filtering iterator in the query plan. On line 11 there’s a nested loop join, and on line 12...
All the operators in the query plan are nested inside subQuery1 that is referenced by DFESubquery. All the operators that are pushed down to the DFE engine have names that start with a DFE prefix. As mentioned above, the whole openCypher query plan is executed by the DFE, so as a ...