…to a single table, where probably only recently read records will be cached, resulting in more disc reads. 2. If you need to…queries on any other column, these could easily be quicker on a partitioned table, as Mysql…Selects…rows… for example, if you need to…
Post: Implications of Metadata Locking Changes in MySQL 5.5
February 1, 2013 By 9 Comments
…column to the table while a transaction in REPEATABLE-READ isolation mode is ACTIVE. session1 > select @@tx_isolation; +—————–+ | @@tx_isolation | +—————–+ | REPEATABLE-READ | +—————–+ 1 row…
Post: High-Performance Click Analysis with MySQL
December 22, 2008 By 13 Comments
…columns to support these queries. But beware of denormalizing with character data; try to make your rows…to think about how to avoid enormous tables that are hard to…single row created from many rows, and if the many rows don’t match completely, the single…queries that read a lot of rows — MySQL…
Post: How to recover deleted rows from an InnoDB Tablespace
February 20, 2012 By 4 Comments
…how it could be possible to recover, on some specific cases, a single table from a full backup in order to…to_date); Query OK, 3 rows affected (0.01 sec) Records: 3 Deleted: 0 Skipped: 0 Warnings: 0 mysql (employees) > select…
Post: Multi Column indexes vs Index Merge
September 19, 2009 By 31 Comments
…columns i1 and i2 independent in this case each selecting about 1% rows from this table which contains about 10M rows. mysql…query scans a lot of rows and completed in about 290ms So we can see index merge indeed improves performance compared to single…
Post: MySQL Indexing Best Practices: Webinar Questions Followup
August 16, 2012 By 4 Comments
…SELECT * FROM TBL WHERE hash=crc32(‘string’) AND string=’string’ The other thing you need to consider is string comparison in MySQL…to redesign schema and queries to make it work well. Q: how does a index be used having an index on one column…
Post: How number of columns affects performance ?
September 28, 2009 By 12 Comments
…single tinyint column which is almost shortest type possible (CHAR(0) could be taking less space), table with 1 tinyint column…to t99v1 table and repeated the query: mysql [localhost] {msandbox} (test) > select max(t1+0) from t99v1; +———–+ | max(t1+0) | +———–+ | 0 | +———–+ 1 row…
Post: Multi-Column IN clause - Unexpected MySQL Issue
April 4, 2008 By 21 Comments
…row in set (0.00 sec) As you can see just using multiple column IN makes MySQL to…MySQL feature out there. For given application case we could simply rewrite query using more standard single column IN clause: mysql> explain SELECT…
Post: Shard-Query turbo charges Infobright community edition (ICE)
May 6, 2011 By 23 Comments
…MySQL data sets and queries. Another advantage is that it works with all MySQL storage engines. This set of benchmarks evaluates how…to the staging tables, omitting the dimension columns from the projection, instead replacing them with the dimension keys: select…
Post: Shard-Query adds parallelism to queries
November 15, 2010 By 18 Comments
…MySQL never takes advantage of more than a single CPU when aggregating data and fetching rows from the buffer pool, with respect to a single query…
