… brings. Multi Range Read With traditional secondary index lookups, if the columns that are being fetched do not belong to the secondary index definition… that traditional index lookup (for non-index-only columns) involves, reading an index record, and then using the PK column value in the index record to make a lookup in the PK. Both these lookups are performed in a single call…
Post: Multi Column indexes vs Index Merge
September 19, 2009 By 30 Comments
… see index merge indeed improves performance compared to single index only but it is by far better to use multi column indexes. But the problems with Index… combined index in this case. In case you’re using OR between columns – single column indexes are required for index merge to work and combined indexes can…
Post: Multi-Column IN clause - Unexpected MySQL Issue
April 4, 2008 By 20 Comments
… of urls. To save on indexes instead of using URL we index CRC32 of the URL which allows… feature. I should not be surprised though as multi-column in is not the most used MySQL feature… we could simply rewrite query using more standard single column IN clause: mysql> explain SELECT url FROM 106pages….
Post: 3 ways MySQL uses indexes
September 12, 2009 By 27 Comments
… column in explain plan to see how many index parts are actually used for row lookup. Very common problem I see is multi column indexes… uses single index – there are more complex rules of how indexes will be used if you look at multiple indexes usage with “index merge” Using Index…
Comment: How to find wrong indexing with glance view
August 22, 2008 By 27 Comments
… drop a few columns from that index without losing any performance. And there’s the problem of mysql choosing single column indexes where multi-column indexes are present, and wasting memory and disk space. I still think that single column indexes make more sense…
Post: MySQL Users Conference - Innodb
May 9, 2007 By 6 Comments
…to specify single page size for Innodb table, while data pages and pages for different indexes may …for statement duration for Inserts with auto-increment column. This starts giving you problems if you … for full statement duration. The problem with multi value inserts however is the following – even …
Comment: Why InnoDB index cardinality varies strangely
September 28, 2009 By 5 Comments
… is much worse than it is sounds. For single-column indexes we get variations. For multi-column indexes we have problems. Lets consider CREATE TABLE T…. In their opinion the behavior is inherent, as sampling of indexes happen independently. I guess, expectations of optimizer are: 1) x1…
Post: High-Performance Click Analysis with MySQL
December 22, 2008 By 13 Comments
…, with no delays. Finally, the analysis is usually multi-dimensional. The typical user wants to be …if your write workload exceeds the capacity of a single server (or if you’re using replication, the …will share a set of primary key columns. And not only will every index be a little narrower, the …
Post: Falcon Storage Engine Design Review
January 12, 2007 By 19 Comments
… now even laptops are getting multi cores so we can forget about spinlocks wasting CPU time on single CPU boxes without much… how small indexes really are. [-] No “using index” Falcon always have to check the row data even if you retrieve only columns which are in the index. I think this is big gotcha as having index covered queries is great…
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 139 Comments
…and rarely accessed data stored in different servers), multi-server partitioning to use combined memory and …single thread depending on system and table structure. Now if you data fully on disk (both data and index… with over 30 millions of rows. “val” column in this table has 10000 distinct value, …
