… look into something interesting with the index cardinality statistics reported by InnoDB tables. The cardinality varies because it’s derived from estimates… into was why the cardinality varies in a particular pattern. Here I’ll grab a bunch of cardinality estimates from sakila.film…
Post: ANALYZE: MyISAM vs Innodb
September 3, 2008 By 9 Comments
… see after running ANALYZE we have exact cardinality for i and c columns, with cardinality for the pair (c,i) looks a… table we do not get NULL cardinality as with MyISAM but instead we get very wrong cardinality which shows us index prefix…” key cardinality is overestimated 3 times, “c” key prefix cardinality is underestimated 5 times and the combined (c,i) key cardinality is overestimated…
Comment: Star Schema Bechmark: InfoBright, InfiniDB and LucidDB
January 12, 2010 By 48 Comments
… to Q4 series. In addition there is an Aggregation/Join Cardinality Dimension, within each query series the predicates eliminate more rows… the queries like this, grouping by Complexity and Aggregation/Join Cardinality, where the values are rough estimates of rows being aggregated… InfiniDB, the results are apparently flat across the Aggregation/Join Cardinality Dimension, with about a 4% variation within a series, (except…
Post: How (not) to find unused indexes
October 16, 2009 By 2 Comments
… | Using where | +—-+————-+——-+——+—————+——+———+——+——-+————-+ 1 row in set (0.01 sec) The cardinality of status index is woeful, but provided that the application… where applications have good selectivity with some queries despite what cardinality shows. Not convinced? Here’s reason number two: CREATE…
Post: Multiple column index vs multiple indexes
August 22, 2008 By 13 Comments
… of other tables with same data just with really low cardinality with i and j having just 3 values each. The… – - Note1: Q1 will not use Index Merge technique for low cardinality table but instead pick to do single index scan. I… but in case of high cardinality multiple index configuration. Note4 Q5 was just run on high cardinality tables to show what difference…
Comment: Database problems in MySQL/PHP Applications
August 11, 2006 By 13 Comments
… agreement: “Use Indexes smartly.” Indexing columns that have very low cardinality will often be a waste of resources because the optimizer just won’t use them. Cardinality can be thought of as “how unique or common is… for in this table?” An index that has very high cardinality (as high as the number of rows in the table…
Post: MySQL Indexing Best Practices: Webinar Questions Followup
August 16, 2012 By 4 Comments
… manually. Q: What are some methods to overcome vastly differing cardinality on a primary key. After running an analyze on a table with 11M rows I’ve seen cardinality range from 19 to over 19,000? Cardinality is property of data so you…
Post: The case for getting rid of duplicate “sets”
May 17, 2011 By 2 Comments
… is stored inside of a histogram in the set. The cardinality and the distribution is always known. Second, computation on the… to hold the set of numbers (and their desired minimum cardinality) to a “search set” table: CREATE TABLE `search_set` ( `val…
Post: Using any general purpose computer as a special purpose SIMD computer
May 16, 2011 By 5 Comments
… any arbitrary degree of parallelism up to, and including, the cardinality of the set. Given that: It is often possible to…, I would like to note that this set has a cardinality of 3088896. This is the maximum theoretical degree of parallelism…
Comment: How to Identify Bad Queries in MySQL
January 11, 2011 By 16 Comments
… comments.” (1) I look at the cardinality (number of records) visited compared to the cardinality send. Have 2 million records been checked…
