…found and returned up to the top level MySQL part for processing …to the tables is “const” MySQL does not count it as access to two tables. In case of “real” access to the data…from sbtest group by k; This only sends 2 rows while scanning 10 … way to see if query is worth optimizing ? – see how many …
Post: How fast can you sort data with MySQL ?
August 18, 2007 By 26 Comments
… table as I used for MySQL Group by Performance Tests to see how much MySQL can sort 1.000.000 rows, or rather return top 10 rows from sorted result set which is the most typical way sorting is used in practice. I tested full table scan….000.000 of rows were partially sorted but only 10 rows fetched from the data file and sent and only they are counted…
Post: Flexviews - part 3 - improving query performance using materialized views
April 4, 2011 By 20 Comments
…tables used by the above view, as stored in the data dictionary: mysql> select * from flexviews.mview_table…(dashboard_top_customers) to list the top 10 customers …how you can combine both types of views together. The complete method examples show how to create a complete refresh view which reads from…
Post: Shard-Query adds parallelism to queries
November 15, 2010 By 18 Comments
…to diverge into a discussion of how OLAP varies from OLTP, it suffices to…table is partitioned by month which means that MySQL can use partition pruning to reduce the amount of data…padding-left:3px;border-top:1px solid #CCC;border….20541715621952.84753513336182.7391619682312.10 year40.567.0243….
Post: Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
…how much of “load” is not covered by top queries, we have 10% in MISC which means that by reviewing these top…to gather more data about the underlying tables involved and the query execution plan used by MySQL…
Post: How Percona does a MySQL Performance Audit
November 24, 2008 By 17 Comments
…how to read these, there’s a full explanation in our book, High Performance MySQL…to/slow.log By default, this outputs the top 10…to the query or the table. We explain how to…
Post: Aligning IO on a hard disk RAID – the Benchmarks
June 9, 2011 By 13 Comments
…data/mysql socket=/var/run/mysqld/mysqld.sock innodb_file_per_table = true innodb_data…to IO alignment yourself. In this case offset is correct, but file system is unaware how to align files properly. 4. Partition table…
Post: High-Performance Click Analysis with MySQL
December 22, 2008 By 13 Comments
…to provide reports to their clients. Clicks by day, by customer, top ads by clicks, top…data processing in MySQL, you’re going to end up heavily I/O bound. Listen to any of the talks at past MySQL conferences from…to think about how to avoid enormous tables that are hard to…
Post: MySQL EXPLAIN limits and errors.
July 24, 2006 By 6 Comments
…table and so how much rows will be stored to temporary table. Sometimes it is enough to perform sorting or use temporary table…data from other tables. No information about using disk for sort or temporary tables MySQL…
Post: 3 ways MySQL uses indexes
September 12, 2009 By 28 Comments
…MySQL decides to pass it on. There are some workarounds you can use though. Using index to read data…from the same page but the rows itself can be scattered across many pages requiring potentially a lot of IOs. On top…
