query optimization in dbms

MVCC schema. The cost estimate in the execution plan is not equal to the actual cost of execution. So even if the statistical information is accurate, the optimizer's execution plan may not be a crime-superior. For example, sometimes an execution plan needs to read more pages, but his cost is even smaller. Because if these pages are sequential read or the pages are already in memory, the cost of access will be minimal. MySQL level and only know those pages in memory, those on disk, so the

Tags: MySQL database If a large table contains millions, tens of millions, or even hundreds of millions of data records, the query results should be queried in real time within 10 seconds. What should I do? How to optimize it? In my current project, there is a table with more than 10 million rows of data and more than 3 GB of data. Now we need to perform query statistics on the data in the table. Previo

ORDER (40 + 2 = 42 pages). The output table contains about 95 rows on each page, with a total of 160 pages. Writing and accessing these pages triggers 5*160 = 800 reads and writes, and the index reads and writes 892 pages. 3. Connect the output and the part to get the final result: SELECT pvvn_by_pn. *, part. part_desc FROM pvvn_by_pn, part WHERE pvvn_by_pn.part_num = part. part_num Drop table pvvn_by_pn In this way, the query reads pvvn_by_pn sequen

can greatly optimize the query speed, basically can be completed within dozens of milliseconds. The restriction is only used to explicitly know the ID, but when the table is established, the Basic ID field is added, which brings a lot of traversal to the paging query.There is another way to do this:selectfromwhereid1000001limit100;Of course, you can also use in the way to query, this method is often used i

Label:MySQL Database optimization pt-query-digest use I. Introduction of PT-QUERY-DIGEST Tools Pt-query-digest is a tool for analyzing MySQL slow query, which can analyze Binlog, general log, Slowlog, or through show Processlist or the MySQL protocol data captured by Tcpdump

SQL Server query performance optimization analysis transactions and locks (I) SQL Server query performance optimization analysis transactions and locks (ii) SQL Server query performance optimization analysis transactions and locks

Essential SQL query optimization techniques to speed up Website access and SQL access In this article, I will introduce how to identify queries that cause performance problems, how to locate their problems, and how to quickly fix these problems and other methods to speed up the query. You must know that a website with quick access can be liked by users, help web

The following articles mainly describe five useful methods for MySQL query optimization. Anyone familiar with SQL statements knows that if you want to operate a task, SQL statements can be written in many ways, but the query performance varies with different writing methods. This article lists five MySQL query

meaning of the expression "specific optimizations" in the table above Q Contrast S8 and S9, can be seen, toprowdb to S9 did not provide optimization, and PostgreSQL, MySQL can optimize, this toprowdb need to work hard Q contrast S11, toprowdb and MySQL are stronger than PostgreSQL In the first part of the subquery optimization, we found that MySQL's in subquery opti