June 18, 2013

Post: ORDER BY ... LIMIT Performance Optimization

… filesort. The solution for this problem is ether extending your indexes so MySQL Optimizer does not have …use indexes, even if it is quite fast: mysql> explain select * from test order by k limit 5; +—-+————-+——-+——-+—————+——+———+——+———+——-+ | id …

Post: Join Optimizations in MySQL 5.6 and MariaDB 5.5

… also look at, in this post. Now let me briefly explain these optimizations. Batched Key Access Traditionally, MySQL always uses Nested… BKA With this optimization the idea of MRR is further extended to improve join performance. As I told you above, when… algorithm only works with equi-joins. Now let me briefly explain how hash join algorithm works. Suppose you have two tables…

Post: MySQL File System Fragmentation Benchmarks

… is close, the difference is perhaps explained by the fact files needed to be constantly extended (meta data updates) and reopened for… and when better again for 10000 tables. I can’t explain why it is a bit worse for 1000 tables thought…. A bit better performance in this case can be perhaps explained but a bit larger increment how tablespaces are allocated comparted…

Comment: Wishes for new "Pure PHP" MySQL driver

… simply can enable explain profiling and get nice table with your query explains and tuning advice simply by enabling explain debug option that… manually. You can create a child from mysqli class and extend it with tons of custom behavior but that would be…

Comment: EXPLAIN EXTENDED can tell you all kinds of interesting things

I use explain extended to know the table name that the column belongs. I lot of programmers do not mention the table alias before the column name in the query, if the column name is unique. I find it easy to use extended to know the table name.

Post: JOIN Performance & Charsets

… 400,000. The data set fit easily in memory. mysql> EXPLAIN EXTENDED SELECT SQL_NO_CACHE COUNT(t1.char_id) > FROM t1… execution time of 3.12 seconds and had the following EXPLAIN: *************************** 1. row *************************** id: 1 select_type: SIMPLE table: t1 type…

Comment: Feature Idea: Finding columns which query needs to access

Does it have to be an extension to EXPLAIN? A standalone script (say written in perl or so) would … it would be interresting to have it also available like EXPLAIN EXTENDED or something…

Comment: Extended EXPLAIN

Peter, a small correction: EXPLAIN EXTENDED was introduced in 4.1, not in 5.0 (and it is documented at http://dev.mysql.com/doc/refman/4.1/en/explain.html)

Post: Sphinx search performance optimization: attribute-based filters

… text columns are always indexed and using the very powerful extended query syntax you can do search against certain columns only… first time, it maybe a little confusing, but let me explain. Query returned 20 rows because unless you specify an explicit…

Post: Submit your proposal for Percona Live London 2012 Now !

… code Level and can share some prospective about internals or explain how features work in depth it would be a gem… just advanced topics for veterans. The call for papers is extended until August 26th to give you a few more days…