… note that the following changes were made in the MySQL config: optimizer_switch=’index_condition_pushdown=off’ optimizer_switch=’mrr=on’ optimizer… on IO bound workload, mentioned above. Counter Name MySQL 5.5 MySQL 5.6 MySQL 5.6 w/ read_rnd_bufer_size=4M… Sometimes both for MariaDB 5.5 and MySQL 5.6, the optimizer chooses the wrong query execution plan. Let’s take a…
Comment: How Does Semisynchronous MySQL Replication Work?
March 15, 2012 By 23 Comments
Hi Mark, Which part of the following article is wrong according to you ? http://www.dbi-services.com/index.php/blog/entry/mysql-data-high-availability-with-semi-synchronous-replication Thanks for your feedback, best regards
Post: When EXPLAIN estimates can go wrong!
October 13, 2011 By 7 Comments
… as MySQL uses “the number of rows” estimation to pick and choose indexes and it could really be picking up a wrong index simply because of the wrong estimate. The customer reported… is used to generate index cardinality estimates which are then in turn used by MySQL to pick and choose indexes and hence is…
Post: 3 ways MySQL uses indexes
September 12, 2009 By 27 Comments
… MySQL can use indexing, getting wrong ideas on what query performance they should expect. There are 3 main ways how MySQL can use the indexes… further index parts. If you have A BETWEEN 5 AND 10 AND B=5 for the same index MySQL will use the index… but… how MySQL uses single index – there are more complex rules of how indexes will be used if you look at multiple indexes usage with “index…
Post: Should you name indexes while doing ALTER TABLE ?
May 28, 2008 By 10 Comments
… the indexes. Lets first speak about naming. If you do not specify index name MySQL will name index by the first column of index created, if there is such index already it will… auto generated index names you may drop the wrong indexes as part of upgrade process just because somebody was adding custom indexes to the…
Post: MySQL Error Message Nonsenses
March 16, 2008 By 7 Comments
… as give some better explanation on what is wrong. The new parser for MySQL was spoke since 5.0 times but it…@sl1 ~]$ perror 124 OS error code 124: Wrong medium type MySQL error code 124: Wrong index given to function The same code instead of… absolutely misleading error messages produced when this limit is reached: mysql> insert into yt values (66666); ERROR 1114 (HY000): The table…
Post: What's required to tune MySQL?
July 27, 2011 By 4 Comments
… you should expect to deliver huge wins. If MySQL is actually badly configured, you can hurt its … at the my.cnf file and see something wrong. Usually, though, the consultant needs to look at… queries The schema design (table design, data types, indexing, etc) The data itself All of these things …
Post: MySQL 6.0 vs 5.1 in TPC-H queries
March 25, 2008 By 17 Comments
… is ‘Using Index condition’, what I was able to find is Baron’s bug with no mention in MySQL 6.0 manual… I/O we had during execution of query, as MySQL used index to scan rows and then did access to data to… works. What else worth to mention here is that MySQL is wrong choosing index scan here. If we try to execute query with…
Post: Troubleshooting MySQL Upgrade Performance Regressions
February 15, 2012 By Leave a Comment
… old one by using hints such as STRAIGHT_JOIN, FORCE INDEX, BIG_RESULT/SMALL_RESULT. Check whatever stats are the same… SHOW INDEXES FROM for tables involved and check cardinality) Different stats can often cause different plans. Run ANALYZE TABLE on both MySQL… the faster plan may be wrong plan from optimizer standpoint and updating stats may cause old MySQL Version to get slower plan…
Post: How Percona does a MySQL Performance Audit
November 24, 2008 By 17 Comments
…, and I don’t see anything wrong there. So at this point, it looks like MySQL is probably a good place to… checking for default users in the mysql.* tables, running mk-duplicate-key-checker to find redundant indexes, and so on. As with…. You cannot consider any one of these factors (schema, queries, indexing) in isolation, because they are tightly bound together, and tweaking…
