SELECT COUNT(*) before every INSERT? why?

[rakhbari]

I've just successfully deployed an entity bean and ran some tests against it. It's working, but when I look at the server.log, I'm seeing what appears to be un-necessary calls right before a create:

2003-08-08 11:16:55,573 DEBUG [org.jboss.ejb.plugins.cmp.jdbc.JDBCCreateEntityCommand.Realm] Create: pk=2199139893
2003-08-08 11:16:55,573 DEBUG [org.jboss.ejb.plugins.cmp.jdbc.JDBCCreateEntityCommand.Realm] Executing SQL: SELECT COUNT(*) FROM Realm WHERE guid=?
2003-08-08 11:16:55,583 DEBUG [org.jboss.ejb.plugins.cmp.jdbc.JDBCCreateEntityCommand.Realm] [Realm.ejbCreate] Executing SQL: INSERT INTO Realm (guid, version, parent_guid, name, title, locale_language, locale_country, locale_variant, create_date, deleted) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
2003-08-08 11:16:55,583 DEBUG [org.jboss.ejb.plugins.cmp.jdbc.JDBCCreateEntityCommand.Realm] Rows affected = 1

JBoss appears to be doing a SELECT COUNT(*) before every INSERT. This is quite a bit of overhead for every insert call, isn't it? What's the purpose? Is it because my "guid" field is a PK and it's just trying to make sure that it doesn't really exist to begin with?

I verified the JBoss CMP source code and sure enough, the call to insert the entity has this in it:

if(entityExists(pk)) {
throw new DuplicateKeyException("Entity with primary key " + pk + " already exists");
}
insertEntity(ctx);

The call to entityExists(pk) has the SELECT COUNT (*) in it.

Can someone enlighten me as to why JBoss is doing it like this?

Thanks.

RA

[stuermer_g]

I think you got it. It's just to verify that the Dataset is unique.
If you don't use the same PK in the Database and in the EJB you won't get an error if you insert the dataset. I know that sounds a little bit strange but perhaps there are situations where it can be useful.

Best regards

Peda

[samart]

I think its strange behavior too.

turn it off :

<jbosscmp-jdbc>


java:/datasourcedatasource>
<datasource-mapping>Sybase</datasource-mapping>
<entity-command name="no-select-before-insert"/>

[mkotsbak]

This option seems to be added in jboss 3.2.x (as I can see in the DTD)