…. It is very typical to hear complains about MySQL interactive performance – serving simple standard web traffic is drastically impacted when some… from innodb_sys_tables as t inner join innodb_sys_indexes as i using(table_id) inner join innodb_buffer_pool_pages_index as… makes workload extremely IO bound hence such drop in performance. The performance of mysqldump is impacted too because we now have 2…
Comment: Why MySQL could be slow with large tables ?
April 12, 2007 By 139 Comments
… lot of counting. Does this look like a performance nightmare waiting to happen? Thanks, Will SELECT Q…) INNER JOIN tblanswersets ASets USING (answersetid) INNER JOIN tblanswersetsanswers_x ASAX USING (answersetid) INNER JOIN tblanswers A USING (answerid) LEFT JOIN (tblevalanswerresults e1 INNER JOIN…
Comment: Database problems in MySQL/PHP Applications
August 11, 2006 By 12 Comments
… normalize your data however it > does not always bring good performance. Joins are expensive and > you can often do much better with…=1) Ouch! Use INNER JOIN for this instead because it allows the optimizer to use the indexes to join rows together, potentially preventing… kind of JOIN to use so that the right number of rows are scanned and returned. SELECT * FROM articles INNER JOIN users ON…
Comment: Is there a performance difference between JOIN and WHERE?
November 5, 2011 By 25 Comments
… three ways to do this, but which one would be performing best considering the first table to be huge (100 thousands… table_1 a INNER JOIN table_2 b ON b.id = SET a.value = b.value WHERE a.id = 3) join, both ids in ON clause UPDATE table_1 a INNER JOIN table_2 b ON a.id…
Comment: Is there a performance difference between JOIN and WHERE?
November 5, 2011 By 25 Comments
… three ways to do this, but which one would be performing best considering the first table to be huge (100 thousands… above 2) join, one id in ON clause, the other id in where clause UPDATE table_1 a INNER JOIN table_2 b….value WHERE a.id = 3) join, both ids in ON clause UPDATE table_1 a INNER JOIN table_2 b ON a.id…
Post: Eventual Consistency in MySQL
November 18, 2011 By 8 Comments
… learn that the enforcement of foreign keys incurs a significant performance overhead.1,2 MySQL allows us to set FOREIGN_KEY… data satisfies RI. At some point we do want to perform some quality control, to verify consistency. How can we do… NULL;’ ) AS _SQL FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE K INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE P ON (K.TABLE_SCHEMA…
Comment: Using delayed JOIN to optimize count(*) and LIMIT queries
August 23, 2007 By 22 Comments
… acts a little weard:P While this works when performing LEFT JOINS, with INNER JOINS it’s a different thing. Let’s say we… & 10000, like in the above example, but let’s perform an innerj join instead… The first subquery will return the requested 10…
Post: Advanced index analysis with mk-index-usage
November 11, 2010 By 2 Comments
… up an SSH tunnel from my laptop to the MySQL Performance Blog server — another 30 seconds. Now I’m set up… / total_cnt * 100 AS pct FROM index_usage AS iu INNER JOIN ( SELECT query_id, db, tbl, SUM(cnt) AS total_cnt… fraction of queries to have very different performance, in general — you want consistent performance. Maybe the performance IS consistent, we don’t know…
Comment: How much overhead is caused by on disk temporary tables
August 17, 2007 By 26 Comments
… the filesort GROUP BY implementation “Later one of the clients performing group bys on tens of millions of rows complained and….name , e.id , sum(q.score) score FROM exam e INNER JOIN question q ON e.id = q.exam_id GROUP BY…
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 139 Comments
… rows and delivers great performance. What could be the reason ? The reason is normally table design and understanding inner works of MySQL… be closed. Joins Joins are used to compose the complex object which was previously normalized to several tables or perform complex queries finding… less full table scan may be faster. Avoid joins to large tables Joining of large data sets using nested loops is very…
