Recipe 10.22 Reloading the Schema Cache
10.22.1 Problem
You want to reload the schema cache so that schema extensions take effect immediately.
10.22.2 Solution
10.22.2.1 Using a graphical user interface
Open the Active Directory Schema snap-in.
In the left pane, click on Active Directory Schema.
Right-click on the label and select Reload the Schema.
10.22.2.2 Using a command-line interface
You can reload the schema by using the ldifde utility and an LDIF file that contains the following:
dn: changetype: modify add: schemaUpdateNow schemaUpdateNow: 1 -
If the LDIF file were named reload.ldf, you would run the following command:
> ldifde -v -i -f reload.ldf
10.22.2.3 Using VBScript
set objRootDSE = GetObject("LDAP://dc1/RootDSE")
objRootDSE.Put "schemaUpdateNow", 1
objRootDSE.SetInfo
WScript.Echo "Schema reloaded"
10.22.3 Discussion
Each domain controller maintains a complete copy of the schema in memory to make access to the schema very fast. This is called the schema cache. When you extend the schema on the Schema FSMO role owner, the change is written to the schema cache, and not committed to disk yet. The schema automatically commits any changes to the schema every five minutes if a change has taken place, but you can also do it manually/programmatically by writing to the schemaUpdateNow operational attribute of the RootDSE on the Schema FSMO role owner. Once that is done, any changes to the schema cache are written to disk.
It is necessary to force a schema cache update if your schema extensions reference newly created attributes or classes. For example, lets say that we want to create one new auxiliary class that contains one new attribute. To do that we would first need to create the attribute and then create the auxiliary class. As part of the auxiliary class' definition, we would need to reference the new attribute, but unless we reload the schema cache, an error would be returned stating that the attribute does not exist. For this reason we need to add an additional step. First, create the attribute, then reload the schema cache, and finally, create the auxiliary class. Here is what an LDIF representation would look like:
dn: cn=rallencorp-TestAttr,cn=schema,cn=configuration,dc=rallencorp,dc=com changetype: add objectclass: attributeSchema lDAPDisplayName: rallencorp-TestAttr attributeId: 1.3.6.1.4.1.999.1.1.28.312 oMSyntax: 20 attributeSyntax: 2.5.5.4 isSingleValued: FALSE searchFlags: 1 dn: changetype: modify add: schemaUpdateNow schemaUpdateNow: 1 - dn: cn=rallencorp-TestClass,cn=schema,cn=configuration,dc=rallencorp,dc=com changetype: add objectclass: classSchema lDAPDisplayName: rallencorp-TestClass governsId: 1.3.6.1.4.1.999.1.1.28.311 subClassOf: top objectClassCategory: 3 mayContain: rallencorp-TestAttr
10.22.4 See Also
Recipe 10.7 for adding a new attribute to the schema and Recipe 10.9 for adding a new class to the schema
