Re: atomic number generator

["Kurt D. Zeilenga" <Kurt@OpenLDAP.org>]

At 11:22 AM 11/22/2004, John Woodell wrote:
>Is this the correct way to increment and provision numbers from LDAP?

Please direct general LDAP questions to a general LDAP mailing
list, such as <ldap@umich.edu>.  See <http://www.openldap.org/lists/>
for this list's charter.

Kurt



>-----------------------------
>
>## lookup current number
>% /usr/local/bin/ldapsearch -LLL -b 'ou=Utils,o=ACME,c=US' employeeNextNumber
>dn: cn=Registry,ou=Utils,o=ACME,c=us
>employeeNextNumber: 8018
>
>## delete current number and increment
>% /usr/local/bin/ldapmodify ...
>dn: cn=Registry,ou=Utils,o=ACME,c=us
>delete: employeeNextNumber
>employeeNextNumber: 8018
>-
>employeeNextNumber: 8019
>modifying entry "cn=Registry,ou=Utils,o=ACME,c=us"
>
>## entire operation will fail if repeated
>% /usr/local/bin/ldapmodify ...
>dn: cn=Registry,ou=Utils,o=ACME,c=us
>delete: employeeNextNumber
>employeeNextNumber: 8018
>-
>employeeNextNumber: 8019
>modifying entry "cn=Registry,ou=Utils,o=ACME,c=us"
>ldap_modify: No such attribute
>       additional info: modify: delete values failed
>ldif_record() = 16
>
>-------------------------------
>
>>The best approach, if I remember correctly, was proposed by Norbert
>>Klausen and was based in using the atomicity property of modify
>>operations.  If instead of using replace for that attribute you ask in
>>the same Modify operation 'delete' of the old value plus 'add' of the
>>new (incremented) value, you are guaranteeed to either fail if someone
>>got there since you read the old max and tried to increment or succeed
>>and thus preempt anyone else following the same algorithm.  Because
>>all changes in the same modify MUST succeed or all of them MUST fail,
>>according to RFC2251.
>