mysql>set session join_buffer_size=default; 或者 mysql>select /*+ set_var(join_buffer_size=1G) */ * from ...; 1. 2. 3. 4. 5. 接下来详细看下 JOIN BUFFER 的用法。那么 MySQL 里针对 INNER JOIN 大致有以下几种算法, 1. Nested-Loop Join
而Block Nested-Loop Join算法较Simple Nested-Loop Join的改进就在于可以减少内表的扫描次数,甚至可以和Hash Join算法一样,仅需扫描内表一次。其使用Join Buffer(联接缓冲)来减少内部循环读取表的次数。 For each tuple r in R do -- 扫描外表R store used columns as p from R in Join Buffer -- 将部分...
优先优化NestedLoop的内层循环,保证Join语句中被驱动表上Join条件字段已经被索引。 当无法保证被驱动表的Join条件字段被索引且内存资源充足的前提下,不要太吝惜JoinBuffer的设置 5.4 索引失效 建表: 索引失效案例: 1、全值匹配我最爱 2、最佳左前缀法则(重要!):如果索引了多列,要遵守最左前缀法则。指的是查询从...
INNER LOOP JOIN INSERT ... SELECT should I always use WITH (TABLOCK) and how can i verify if minimal logging was performed? Insert "dummy" record into each group Insert 100 million records from one table to another in batches Insert a count(*) into a temp table Insert a new record...
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Using Bitmap Join Indexes for PerformanceIn addition to a bitmap index on a single table, you can create a bitmap join index, which is a bitmap index for the join of two or more tables. A bitmap join index is a space-saving way to reduce the volume of data that must be joined,...
Join methods For example, nested loop, sort merge, hash, and star transformation. DDL statements CREATETABLEASSELECT,CREATEINDEX,REBUILDINDEX,REBUILDINDEXPARTITION, andMOVESPLITCOALESCEPARTITION DML statements For example,INSERT AS SELECT, updates, deletes, andMERGEoperations. ...
join_buffer_size: 262144 keep_files_on_create: OFF key_buffer_size: 33554432 key_cache_age_threshold: 300 key_cache_block_size: 1024 key_cache_division_limit: 100 keyring_operations: ON large_files_support: ON large_page_size: 0
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Block IP in Windows through C# block keyboard and mouse input Bluetooth communication using serial ports Bluetooth turning On and Off from C# BMI CALCULATOR: NaN after height and weight are entered. Bold Some Text in MessageBox? Bring variable into scope from a foreach loop Buffer Overflow in ...