DatabaseMetaData.getColumns() takes long time to return columns for a particular schema of Apache JDO TCK

• Key: DERBY-1996
• Type: Improvement
• Status: Open
• Priority: Major
• Assignee: Unassigned
• Reporter: Andy Jefferson
• Component/s: SQL
• Affects Version/s: 10.2.1.6

Description

When running the Apache JDO "TCK", JPOX needs to query the columns for a particular schema, and so uses DatabaseMetaData.getColumns(null, schemaName, null, null). This takes the order of 3 minutes on a dual-core Pentium 3GHz (with large ram). I've cut the JPOX part down to a stand-alone test (will attach it).

Thing to note is that with only the schema files d_* installed it takes the order of 20secs. When the schema_* files are also installed then performance goes downhill fast (even though they are in different schemas ... all *.sql file represents a different schema). No point in me postulating what could be the issue since you guys are the Derby experts.

Comments

[Andy Jefferson]

To run the test, i've included Maven1 files.

maven clean installschema
will install all *.sql files

maven jar runtest
will run a simple JDBC test of DatabaseMetaData.getColumns()

[Andy Jefferson]

Any comment on when (approx) DatabaseMetaData.getColumns will be capable of giving reasonable performance in situations like this? or is there some SELECT that we can do ourselves to get the same basic information without having to go through getColumns() ?? Thx

[Rick Hillegas]

Hi Andy,

It doesn't look like anyone is working on this issue. You can vote for it and you can advocate for it on derby-dev or derby-user. Note that there are 3 weeks left before we cut the 10.4.2 release.

The following query may give you some of what you need. I have no idea how this query performs on your schema:

select s.schemaname, t.tablename, c.columnname, c.columnnumber, c.columndatatype
from sys.sysschemas s, sys.systables t, sys.syscolumns c
where c.referenceid = t.tableid
and t.schemaid = s.schemaid
and t.tabletype = 'T'
order by s.schemaname, t.tablename, c.columnname, c.columnnumber
;

A couple points about this query:

o You can adjust this query by consulting the layout of the system tables. That layout is described in the Derby Reference Guide.

o The columndatatype column is an object of type org.apache.derby.catalog.TypeDescriptor. That class is not in Derby's public API and therefore is not guaranteed to be stable across releases (although my sense is that it has tended to evolve in upward-compatible ways).

[Knut Anders Hatlen]

Triaged for 10.5.2.