… the hash table by using values of the columns participating in the equijoin condition. The hash table is accessed by using a hash function… as compared to BKA MySQL 5.6, and 965x less time as compared to BNL MySQL 5.5. So hash join gives us… that MySQL 5.5 beats both BKA of MySQL 5.6 and Hash Join of MariaDB 5.5. In IO bound test MySQL 5…
Post: Join Optimizations in MySQL 5.6 and MariaDB 5.5
April 4, 2012 By 4 Comments
… build step. After the hash table has been created, rows from table t2 are read and hash function is applied to the columns participating in the join condition and then a hash table lookup is performed, on the hash… a look at the status counters. Counter Name MySQL 5.5 MySQL 5.6 MySQL 5.6 w/ join_buffer_size=6M & read…
Post: MySQL Indexing Best Practices: Webinar Questions Followup
August 16, 2012 By 4 Comments
… reasonable performance optimization. (Keep in mind that the prefix adaptive hashing would fail here, because the first 10 or so characters… comparison in MySQL is case insensitive by default while hash comparison will be done case sensitive unless you lowercase string before hashing. I… index order MySQL gets data in already sorted order and looks at “one group at the time”, computing aggregate functions as needed…
Post: Ultimate MySQL variable and status reference list
January 8, 2011 By 4 Comments
… the amazing MySQL manual, especially the option and variable …fieldsblogpercona.commanual Com_show_function_codeblogpercona.commanual Com_show_function_statusblogpercona.commanual Com_…innodb_adaptive_flushingblogpercona.commanual innodb_adaptive_hash_indexblogpercona.commanual innodb_additional_mem_…
Comment: Speeding up GROUP BY if you want aproximate results
March 8, 2008 By 24 Comments
… theory CRC32 is not a hash function… but MySQL does not offer any fast integer hash functions…. MD5/SHA1 are crypto hash functions which is completely different… which would be far more than for hash function of given bits ? Here is example: mysql> select count(distinct page) from (select page…
Post: DROP TABLE and stalls: Lazy Drop Table in Percona Server and the new fixes in MySQL
June 22, 2012 By 33 Comments
… the implementations. Lazy Drop Table in Percona Server The main function that is responsible for cleaning the bufferpool in the event… reader-writer shared lock on the latch protecting the Adaptive Hash Index (AHI) Scan the buffer pool and for each page… latch protecting the AHI Drop Table in Oracle MySQL >= 5.5.23 The main function that is responsible for cleaning the bufferpool…
Post: Using any general purpose computer as a special purpose SIMD computer
May 16, 2011 By 5 Comments
… perspective, one must run a function on a large amount of input. Often times, the same function must be run on many… the workers to complete, but you can register a callback function to handle the output of each input asynchronously, if you…, and because I chose to create six hash “buckets” in the table. This allows MySQL to set up a sequential scan over…
Post: High-Performance Click Analysis with MySQL
December 22, 2008 By 13 Comments
… in many different ways on demand, often to support the functionality of the application as well as to provide reports to… large data sets are very expensive. If MySQL supported sort-merge or hash joins, you’d have other possibilities, but it… to maintain, back up, and restore. And the partitioning functionality is not done yet and not fully integrated into the…
Post: Full Text Search Webinar Questions Followup
August 24, 2012 By 5 Comments
… by default, adding relevance sorting to the MySQL queries would make them even slower, I’… it? According to their documentation, MemSQL supports hash indexes and skip list indexes, but not…, and has different requirements for the FT functionality. So one solution may include advanced features…
Post: The new cool MySQL patch has landed! Check your queries performance!
October 31, 2007 By 16 Comments
… RESOLUTION QUERY TIMING This is the original functionality offered by Microslow patch. The new edition…: 1113 LOGGING OF THE REPLICATED STATEMENTS Normally MySQL will not write into slow log any… actually an approximation based on a small hash array representing the entire buffer pool, because…
