…MySQL software appliance. (It used to be hardware-only, if you haven’t been keeping… replication. Data replication is one of the hardest and …MySQL is very bad at. For example, think about using MySQL to find the top N most important rows per group of rows… expand to four tracks). By the way, we are…
Post: How much overhead is caused by on disk temporary tables
August 16, 2007 By 26 Comments
…one will be used depends on the allowed tmp_table_size and also by…keep temporary table. Results: mysql> select count(*) cnt,c from gtest group by c order by…mysql> set global tmp_table_size=1000000000; Query OK, 0 rows affected (0.00 sec) Ahh… I alway forget GLOBAL only…
Post: The MySQL optimizer, the OS cache, and sequential versus random I/O
April 28, 2008 By 17 Comments
… to run with one join order takes…keep this clean. Let’s take a look at the tables. mysql> show table status like ‘fact’\G *************************** 1. row…fact.col2 > some_const group by fact.col1 There… these blocks are used only once and not … million rows / 117 bytes per row / 4096 bytes per read…
Post: Database access Optimization in Web Applications.
September 12, 2006 By 10 Comments
…one way or another if you want to keep…rows are analyzed by the query. For example SELECT COUNT(*) FROM links WHERE domain = ‘mysql.com’; will return only one row while may require to scan hundreds of thousands of rows (or index entries) to do so. Other common killer queries are GROUP BY…
Post: Goal driven performance optimization
December 22, 2008 By Leave a Comment
…MySQL table for larger ones you can log only small portion of them. I usually keep one table per…1 group by h; +——+———-+—————–+——————+ | h | count(*) | avg(wtime) |…2.3949674527604 | 0.51381316608346 | +——+———-+—————–+——————+ 24 rows in…
Post: How much memory can MySQL use in the worst case?
February 12, 2009 By 17 Comments
…ISAM and friends were the only storage engines, which was… calls by doing it all up front in one call… many of those per query. Sorting and grouping and DISTINCT …plan, for example, and keeps it around until the…mysql> set @a := repeat(‘a’, 1024 * 1024 * 100); Query OK, 0 rows affected (2.34 sec) mysql…
