… implicit relationship to parent”> <column name=”id” primaryKey=”true”> column> <column name=”parent_id”>
Post: Implementing SchemaSpy in your MySQL environment
June 4, 2013 By 2 Comments
Post: MySQL Query Patterns, Optimized - Webinar questions followup
June 3, 2013 By 2 Comments
… tradeoff of this solution is that it requires storing another column, and reinitializing the sequence after making certain insert/update/delete…) is an index lookup. Look at the EXPLAIN output — it accesses these first, by looking up the keywords you specify. It… matter, and it would have to match the order of columns in the index. Example: WHERE (last_name, first_name) = (‘Karwin…
Post: The write cache: Swap insanity tome III
April 19, 2013 By 5 Comments
… 30539 21120 2 3 81 13 0 Note the free column going down and the cache one going up and then… “write cache”. A quick survey of the servers I have access to showed that the common values are 20 and 40…
Post: Percona XtraDB Cluster 5.5.30-23.7.4 for MySQL now available
April 17, 2013 By 2 Comments
…). Parallel applying would fail in case mixed CHAR and VARCHAR columns would be used in foreign key definitions. Bug fixed #1100496… variable innodb_thread_concurrency has been defined to throttle InnoDB access, and work load contained DDL statements, a cluster node could…
Post: Multi Column indexes vs Index Merge
September 19, 2009 By 31 Comments
… separate indexes on AGE and STATE columns. The better strategy is often to have combined multi-column index on (AGE,STATE). Lets… reflects very large performance difference between full table scan and access through the index, which seems to be about 10x (in… this case. In case you’re using OR between columns – single column indexes are required for index merge to work and combined…
Post: How number of columns affects performance ?
September 28, 2009 By 12 Comments
… less space), table with 1 tinyint column and char(99) column and table with 100 tinyint columns. The former two tables have the… which does not depends on number of columns. Another interesting observation is access speed to different columns. the max(t1) and max(t99) were taking the same time which means there is no penalty for accessing column which…
Post: Multiple column index vs multiple indexes
August 22, 2008 By 13 Comments
… questions raised about Index Merge on Multiple Indexes vs Two Column Index efficiency. I mentioned in most cases when query can… in milliseconds. Query 1000 – 2 indexes 1000 – 2 columns 3 – 2 indexes3 – 2 columns Q1 20 0.2 6940 2530 Q2 25… to force index merge as you can do with index accesses in general. Note2 Q2/Q3 can’t use Index Merge…
Post: Database access Optimization in Web Applications.
September 12, 2006 By 10 Comments
… you can use. Just remember avoiding accessing database is the best way you can optimize database access. This applies to anything else… ORDER BY rank query is such – adding index on rank column maxes this query to use 10 rows to return 10… UNION (with padding to accommodate different types and number of columns) – this is not a good practice. However if you can…
Post: Feature Idea: Finding columns which query needs to access
November 17, 2006 By 16 Comments
In query examinations it is often interesting which columns query needs to access to provide result set as it gives you ideas… complex queries especially if they do not refer to the columns with table prefix it may take a while to figure our where these columns come from and so how they can be optimized.
Post: Query_cache and column level privileges
August 6, 2007 By 5 Comments
… we were puzzled by question how query_cache works with column level privileges. The question was appeared as we discovered function… to know which columns are accessed. Looking into source code I found out that in the case when table has column level privileges… the initial assumption – the query that includes tables with defined column level privileges can’t be cached – but actually even more…
