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A slow query event caused by misjudgment of the online mysql optimizer. mysql misjudgment Preface: After receiving the crazy slow query and request timeout alarm, metrics analyzes the exception of the
When you submit a query, MySQL will analyze it to see if some optimization can be done to make it faster to process the query. This section describes how the query optimizer works. If you want to know the optimization methods used by MyS
Query optimizer of MySQL Query optimization series (1) when you submit a query, MySQL will analyze it to see if some optimization can be done to make it faster. This section describes how the
This article mainly describes the MySQL query optimizer In the MySQL query optimization series. When you submit a query, the MySQL database will analyze it, it mainly depends on whether
When you submit a query, MySQL will analyze it to see if some optimization can be done to make it faster to process the query. This section describes how the query optimizer works. If you want to know the optimization methods used by MyS
In the manual, the query optimizer provides an overview of the tasks of the query optimizer, which is the best solution for discovering the execution of SQL queries. Most query optimizers, including the MySQL
Analysis of MySQL Query Optimizer (1) 1 definition The Mysql Query optimizer selects an appropriate execution path for the query statement. The code of the
Overview of the query optimizer on the manualThe task of the query optimizer is to discover the best scenario for executing a SQL query. Most query optimizers, including the MySQL
-maintenance, when the MySQL version upgrade, this problem is very prominent, you set the optimizer hints will likely make the new version of the optimizer's optimization strategy invalidated. Do not use these hints to change the default execution plan unless specifically required. mysql5.5 and 5.6 have great improvements in all aspects, generally the upgrade is smooth, but it is still recommended to check
To make this query more efficient, add an index to one of the join columns and rerun the explain statement: mysql> ALTER TABLE t2 ADD INDEX (i2);mysql> EXPLAIN SELECT t1.i1, t2.i2 FROM t1, t2 WHERE t1.i1 = t2.i2\G*************************** 1. row ***************************id: 1select_type: SIMPLEtable: t1type: ALLpossible_keys: NULLkey: NULLkey_len: NULLref: N
Label:The purpose of this article is mainly by telling you what the query optimizer does for us, how we do it, to make the query optimizer optimize our SQL, and to enlighten us on how SQL statements are written to be more efficient. So what exactly is MySQL going to do to op
High-Performance MySql evolution (10): Limitations of the query optimizer bitsCN.com The article "common methods of the query optimizer" lists some common optimization methods of the optimizer. The
When you submit a query, MySQL analyzes it to see if you can do some optimizations to make it faster to process the query. This section describes how the query optimizer works. If you want to know the optimization method used by MySQL
Tags: search test Add Pac--index article body exampleTransfer from http://blog.csdn.net/zhanyan_x/article/details/25294539 --Where execution order--filter more than put in front, and then easier to match, from left to right to execute; The optimizer is optimized intelligently, without user processing--How to view the optimized statementsEXPLAIN EXTENDEDSELECT Sql_no_cache * from db.tableWHERE Is_day=1 and DATE (ex_date) = ' 2015-07-01 '; SHOW WARNINGS
Tags: MySQL query cache optimizerQuery Cache principleWhen MySQL receives a select type of query, MySQL hashes the query to get a hash value and then matches the hash value to the query
Query Cache principleWhen MySQL receives a select type of query, MySQL hashes the query to get a hash value and then matches the hash value to the query cache, if there is no match, The hash value is stored in a hash list, and the
When you submit a query, MySQL analyzes it to see if you can do some optimizations to make it faster to process the query. This section describes how the query optimizer works. If you want to know the optimization method used by MySQL
1. Define The MySQL query optimizer's job is to select the appropriate execution path for the query statement. The code for the query optimizer is generally variable, which is not the same as the storage engine. Therefore, you need to understand how the latest version of th
Without a statement, speak directly:The federated index in the Babysitter_account table is as follows (developing a federated index that the small partners have built themselves, did you find it inappropriate?) ）：KEY ' flag ' (' flag ', ' user_id ', ' account_id ')Used to think:1.SELECT Account_id,weibo_id,weibo_type from Babysitter_account WHERE user_id between and 10000 and flag=0;2.SELECT Account_id,weibo_id,weibo_type from Babysitter_account WHERE flag=0 and user_id between and 10000;The fir
I. ICPNote the conditions of use of the ICP: Can only be used for level two indexes (secondary index). Explain displays the type value (join type) in the execution plan as range, ref, Eq_ref, or Ref_or_null. And the query needs to access the entire row of data in the table, that is, the query results (index overrides) cannot be obtained directly from the tuple data of level two indexes. The
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