Allowing PostgreSQL to use an index when the query uses the LIKE-operator

Eric Bartels — Wed, 05 Aug 2009 18:31:14 +0000

When enabling search in database its very important to have the appropriate indexes defined to make the queries as fast as possible. If your query looks like this (and the appropriate index is defined) the index can be used by the database (the query planner) even with the LIKE-operator. So fast wildcard-searches are possible …

SELECT col1 FROM foobar WHERE col1 LIKE '1234%';

Yes?! Really?!

In one of our production systems this kind of query (when debugged via EXPLAIN / EXPLAIN ANALYZE) return unexpected results. Every time our comparison operator turns from equality = into LIKE the index for the column is fully ignored and instead a full-table scan (sequential scan) is used by the planner. Things are really slow …

I locale you!

After asking Google its seems some more people having this issue, too.
Our database-cluster was initialized with the locale de_DE.utf8. A quick view into the excellent documentation for CREATE INDEX revealed there is an operator class which controls the operators of the index. After adding an index with an operator class for that column the index (“FoobarWildcardIdx”) is now used even when the query contains LIKE.

CREATE INDEX FoobarWildcardIdx ON foobar (col1 varchar_pattern_ops);

Cannot complete this action – error when adding a ContentType to a list

Eric Bartels — Sun, 20 Jul 2008 19:21:03 +0000

Today I got a nice error from my SharePoint development box after I tried to add a certain Content Type to a list.

Cannot complete this action. Please try again. at Microsoft.SharePoint.Library.SPRequestInternalClass.AddField(String bstrUrl, String bstrListName, String bstrSchemaXml, Int32 grfAdd) 
   at Microsoft.SharePoint.Library.SPRequest.AddField(String bstrUrl, String bstrListName, String bstrSchemaXml, Int32 grfAdd)

Tell me

This is an error message every developer fells in love with. Its full of nothing…

Further analysis revealed that there must be a problem with a custom field definition inside that Content Type. Even more investigation found the culprit.

 Type="LookupMulti"
         DisplayName="CustomField"
         Required="FALSE"
         Description="My custom field"
         Group="Custom"
         StaticName="MyCustomField"
         Name="MyCustomField"
         ShowField="Title"
         ShowInDisplayForm="TRUE"
         ShowInEditForm="TRUE"
         ShowInNewForm="TRUE"
         ShowInViewForms="TRUE"
         Mult="TRUE"
         Sortable="FALSE"
         Indexed="TRUE"
         UnlimitedLengthInDocumentLibrary="TRUE"
         List="myList"
         SourceID="{31DCE571-D649-41b8-99D7-448F43FCEAC0}" />

Conclusion

NEVER set the attribute Indexed to TRUE when the field is a Lookup-Field that has the Mult-attribute set to TRUE!