… multiple times…index range lookups. This means MySQL can employ many other optimizations like for example if columns other then the secondary key columns…join algorithm and that is Nested Loop Join. MariaDB has introduced a new join algorithm Hash Join. This join algorithm only works with equi-joins…
Comment: Database problems in MySQL/PHP Applications
August 11, 2006 By 12 Comments
… seen developers ask the database to do row lookups by multiple columns of varchars is likely. Don’t do it. I can…=1) Ouch! Use INNER JOIN for this instead because it allows the optimizer to use the indexes to join rows together, potentially preventing… the column’s possibilities. Also, indexing the full width of very wide columns will take up tremendous amounts of memory and disk. Because indexes…
Comment: How to find wrong indexing with glance view
August 22, 2008 By 27 Comments
… tried multiple combinations, including removing some of the columns that you recommend that I remove and that had performance consequences. I join 2…. I will agree with tgabi, most of the time multi-column indexes are not necessary. If you’re not having issues then… help others by making aware reasons for particular solutions (multi-column index in this case) in MySQL.
Post: ORDER BY ... LIMIT Performance Optimization
September 1, 2006 By 93 Comments
… MySQL using multiple indexes on most selective columns would be good idea for performance of such queries. For example you may put index on… not first in the join order index can’t be used. Sometimes it means breaking normalization and duplicating column(s) you’re going…” is simply indexes column. Note: In some cases even if it is possible to use index to do ORDER BY with JOIN MySQL still…
Post: Heikki Tuuri Innodb answers - Part I
October 26, 2007 By 17 Comments
…current state of Innodb scalability with multiple threads and multiple concurrent transactions ? HT: The scalability in…index is required for fast lookups: it can be used if the columns are the first columns in an index… example, if ORDER and ORDERLINE tables are joined to form a single table), it …
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 139 Comments
…index) you would need 2+ IOs to retrieve the row which means you get about 100 rows/sec. Note multiple…the table with over 30 millions of rows. “val” column in this table has 10000 distinct value, so range…the gap but I doubt it will be closed. Joins Joins are used to compose the complex object which …
Comment: Blob Storage in Innodb
February 17, 2010 By 13 Comments
…, and the id column used to associate rows (1-to-1 relationship). C) Do your hefty queries (with joins, complex where clauses… blob — if you need that for indexing or searching. If you think you need multiple blob columns, then as Peter suggested, consider combining… so easy either, so maybe use multiple “blob-only” tables that have just a few blob columns each — less than 10 he…
Comment: Why MySQL could be slow with large tables ?
January 31, 2008 By 139 Comments
… capital letters are INDEXes and some reference columns in other tables, and the small letters are just data columns that are returned but never used as filters (WHERE/JOIN… preform simple SELECTs in them (not joining them with other tables). Once again, I use multiple inserts into the table, with sets…
Post: Shard-Query EC2 images available
May 11, 2011 By 2 Comments
…distribute splitting and/or loading among multiple nodes as well. Note that…length: 1616904192 Max_data_length: 0 Index_length: 539279360 Data_free: 4194304 …-disk temporary storage for hash joins and other background operations. This… of columns to show (click show/hide to change the columns) That the…
Post: Using Flexviews - part one, introduction to materialized views
March 23, 2011 By 2 Comments
… is really a virtual table. It has columns and rows, just like a database table,… You can add indexes to the MV. Since the data is already joined together and pre-aggregated, CPU and memory usage may be reduced compared to computing the results. You can often generate multiple…
