Emergency

Search Results for: union result

How much memory can MySQL use in the worst case?

I vaguely recall a couple of blog posts recently asking something like “what’s the formula to compute mysqld’s worst-case maximum memory usage?” Various formulas are in wide use, but none of them is fully correct. …


AUTO_INCREMENT and MERGE TABLES

How would you expect AUTO_INCREMENT to work with MERGE tables ? Assuming INSERT_METHOD=LAST is used I would expect it to work same as in case insertion happens to the last table… which does not seems …


Multiple column index vs multiple indexes

(There is an updated version of the content in this post by Percona’s Stephane Combaudon available here.) After my previous post there were questions raised about Index Merge on Multiple Indexes vs Two Column Index …


How adding another table to JOIN can improve performance ?

JOINs are expensive and it most typical the fewer tables (for the same database) you join the better performance you will get. As for any rules there are however exceptions The one I’m speaking about …


MySQL: Data Storage or Data Processing

I was thinking today of how people tend to use MySQL in modern applications and it stroke me in many cases MySQL is not used to process the data, at least not on the large …


Merge Tables Gotcha

I had the interesting customer case today which made me to do a bit research on the problem. You can create merge table over MyISAM tables which contain primary key and global uniqueness would not …


Database access Optimization in Web Applications.

This is pretty simple approach I often use called to optimize web application performance if problem happens with few pages. If we have “everything is slow” problem looking at slow query logs may be better …


ORDER BY … LIMIT Performance Optimization

Suboptimal ORDER BY implementation, especially together with LIMIT is often the cause of MySQL Performance problems. Here is what you need to know about ORDER BY … LIMIT optimization to avoid these problems ORDER BY …


MySQL Query Cache

MySQL has a great feature called “Query Cache” which is quite helpful for MySQL Performance optimization tasks but there are number of things you need to know. First let me clarify what MySQL Query Cache …