…produce an infinite variety of queries. The query optimizer analyzes queries for common patterns the MySQL …solution is that it requires storing another column, and reinitializing the sequence after making …k2, k3) is an index lookup. Look at the EXPLAIN output — it accesses these first, by …
Post: Multi Column indexes vs Index Merge
September 19, 2009 By 31 Comments
…lookup the data. Which method works better depends on selectivity and correlation. If where clause from first column… for this query. The query takes 3370ms if this plan is used. Note the query takes about… performance difference between full table scan and access through the index, which seems to be …
Post: Missing Data - rows used to generate result set
July 20, 2008 By 15 Comments
… all row accessed are created equal (such as full table scan row accesses may be much faster than random index lookups row accesses in the same table) but this is very valuable data point to optimize query anyway. The question… you have WHERE ID%100=0 you can have extra column divisible_by_hundred and keep it indexed. Of course in…
Comment: Detailed review of Tokutek storage engine
April 28, 2009 By 21 Comments
…insertion reads and ordered scans though random point lookups and updates are slow. As we know … orders” in the same table allowing to access all columns while scanning. It is also interesting to … time inserts while InfoBright being column store engine focuses on analytic queries. One thing I would …
Post: Multi Range Read (MRR) in MySQL 5.6 and MariaDB 5.5
March 21, 2012 By 10 Comments
…_key_column FROM tbl WHERE key_column=x This query will roughly be evaluated in following steps, without MRR: SELECT key_column, pk_column FROM… pk_column, we have converted a lot of point primary key lookups to one or more range primary key lookup. Thereby, converting Random access…
Post: Join Optimizations in MySQL 5.6 and MariaDB 5.5
April 4, 2012 By 4 Comments
… interface can instead access the PK by arranging the secondary key values by PK column and then performing the lookup, and then there are other possibilities like InnoDB doing read_ahead by noticing the sequential access… not make much of a difference in the query times. Conclusion BKA improves the query time by a huge margin for IO…
Post: A case for MariaDB's Hash Joins
May 31, 2012 By Leave a Comment
… a lookup in the hash table by using values of the columns participating in the equijoin condition. The hash table is accessed by…_at_trx_commit=2 innodb_flush_method=O_DIRECT query_cache_size=0 query_cache_type=0 optimizer_switch=’index_condition_pushdown… random access of PK, even then it proves to be costly. Also note that the table lineitem, is joined by the column…
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 141 Comments
… created the table with over 30 millions of rows. “val” column in this table has 10000 distinct value, so range 1… of index lookups which could be random accesses. This problem exists for all kinds of applications, however for OLTP applications with queries examining… index accesses – For large data sets full table scans are often faster than range scans and other types of index lookups. Even…
Post: MySQL Indexing Best Practices: Webinar Questions Followup
August 16, 2012 By 4 Comments
… queries. This will use fast primary key for some queries and use key K as covering index for lookup … memory only those portions of them which are accessed frequently. The size of this “working set” can … one column and using order by on another column. do i need to add the index on column using …
Post: InnoDB vs MyISAM vs Falcon benchmarks - part 1
January 8, 2007 By 117 Comments
… only read (SELECT) queries with different typical data access patterns: primary key single row lookup, primary key range lookup, same access types for primary key… good here, because of access only to key column and ‘pread’ syscall is not used. READ_KEY_RANGE Query: SELECT name FROM $tableName…
