INTERNET-DRAFT Kurt D. Zeilenga
Intended Category: Experimental OpenLDAP Foundation
Expires in six months 3 May 2003
LDAP Transactions
<draft-zeilenga-ldap-txn-06.txt>
Status of Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
This document is intended to be, after appropriate review and
revision, submitted to the RFC Editor as an Experimental document.
Distribution of this memo is unlimited. Technical discussion of this
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Copyright 2003, The Internet Society. All Rights Reserved.
Please see the Copyright section near the end of this document for
more information.
Abstract
Lightweight Directory Access Protocol (LDAP) update operations acting
upon entries have atomic, consistency, isolation, durability (ACID)
properties. However, it is often desirable to update two or more
entries as one unit of interaction, a transaction. Transactions are
necessary to support a number of applications including resource
provisioning and information replication. This document defines an
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LDAP extension to support transactions.
Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 [RFC2119].
Protocol elements are described using ASN.1 [X.680]. The term
"BER-encoded" means the element is to be encoded using the Basic
Encoding Rules [X.690] under the restrictions detailed in Section 5.1
of [RFC2251].
1. Overview
This document extends the Lightweight Directory Access Protocol (LDAP)
[RFC3377] to allow clients to group a number of related update
operations [RFC2251] and have them preformed as one unit of
interaction, a transaction. As with distinct update operations, each
transaction has atomic, consistency, isolation, and durability
([ACID]) properties.
This extension uses the grouping mechanism provided by [GROUP] to
relate operations of the transaction. The createGrouping operation is
used to obtain a group cookie which is used to identify operations
which are apart of the transaction. The group cookie can be viewed as
a transaction identifier. The endGrouping operation is used to settle
(commit or abort) the transaction.
2. Specification of a Transaction
Servers implementing this specification SHOULD publish the
transactionGroupingType as a value of the 'supportedGroupingTypes'
attribute contained within the Root DSE.
transactionGroupingType ::= IANA-ASSIGNED-OID
A client wishing to preform a transaction issues a
createGroupingRequest with a createGroupType of
transactionGroupingType and no createGroupValue. A server which is
willing and able to support transactions returns a
createGroupingResponse with a success result code, a
createGroupCookie, and no createGroupValue. Otherwise the server
returns a non-success result code, no createGroupCookie, and no
createGroupValue.
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The client then issues may issue one or more update (add, delete,
modify, rename) requests, each with a GroupingControl indicating they
are to processed as part of the transaction grouping. If the server
is willing and able to attempt to process operation as part of the
transaction, the server returns success. As further processing of the
operation is be deferred until settlement, the operation is considered
still outstanding and its messageID cannot to be reused until after
settlement. If the server is unwilling or unable to attempt to
process the operation as part of the transaction, the server returns a
non-successful result code.
If the server becomes unwilling or unable to continue the
specification of a transaction, the server return the canceled
resultCode for each deferred operation and then issue a endGroupNotice
with a non-success resultCode. Any future use of cookie by the client
will result in a response containing a non-success result code. Upon
receipt of a endGroupingNotice, the client is to discontinue all use
of the grouping cookie as the transaction is null and void.
A client requests settling of transaction by issuing an
endGroupingRequest where the groupingCookie is the group cookie
identify the transaction. The absence of any endGroupingValue
indicates a commit request. The presence of an empty endGroupValue
indicates an abort request. The endGroupValue MUST be empty if
provided.
If the commit response indicates failure, the server may return an
endGroupingValue with the endGroupingResponse. If so, it contains the
BER-encoding of a MessageID [RFC2251] of the update operation
associated with the failure.
3. Settling of the Transaction
Upon receipt of a request to abort the transaction, the server is to
abort the transaction and then return an endGroupingResponse
indicating success.
Upon receipt of a request to commit the transaction, the server
processes the group of update operations as one atomic, isolated
action with each update request being processed in turn. Either all
of the requested updates SHALL be successfully applied or none of the
requested SHALL be applied. If all are applied, the server returns an
endGroupingResponse indicating success. Otherwise, the server returns
an endGroupingResponse indicating the nature of the failure. If the
failure is associated with a particular update operation, the message
ID is returned an attached endGroupingValue. If the failure was not
associated with any particular update operation, no endGroupingValue
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is to be provided.
There is no requirement that a server serialize transactions. That
is, a server MAY process multiple transactions commit requests (from
one or more clients) acting upon different sets of entries
concurrently. A server MUST avoid deadlock.
4. Distributed Directory Considerations
The LDAP/X.500 models provide for distributed directory operations
including server-side chaining and client-side chasing of operations.
This document does not disallow servers from chaining operations which
are part of a transaction. However, if a server does allow such
chaining, it MUST ensure that transaction semantics detailed above are
provided.
This mechanism defined by this document does not support client-side
chasing. Grouping cookies used to identify the transaction are
specific to a particular client/server session.
The LDAP/X.500 models provide for a single-master/multiple-slave
replication architecture. This document states no requirement that
changes made to the directory based upon processing a transaction be
replicated as one atomic action. That is, the client SHOULD NOT
assume tight data consistency nor fast data convergence at slave
servers unless they have prior knowledge that such is provided.
Though this mechanism could be used to support replication, such use
is not described in this document.
The LDAP/X.500 models do not currently support a multi-master
replication architecture and, hence, not considered by this
specification.
5. Security Considerations
Transactions mechanisms and related grouping operations may be the
target of denial of service attacks. Implementors should provide
safeguards to ensure these mechanisms are not abused.
6. IANA Considerations
In accordance with [RFC3383], it is requested that Internet Assigned
Numbers Authority (IANA) make the following assignments.
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6.1. Object Identifier
An LDAP Object Identifier to identify the grouping type defined in
this document is requested.
The following registration template is suggested:
Subject: Request for LDAP Object Identifier Registration
Person & email address to contact for further information:
Kurt Zeilenga <kurt@OpenLDAP.org>
Specification: RFCXXXX
Author/Change Controller: IESG
Comments:
Identifies the LDAP Transactions Grouping Type
6.2. LDAP Protocol Mechanism
Registration of the protocol mechanisms defined in this document is
requested.
Subject: Request for LDAP Protocol Mechansism Registration
Object Identifier: IANA-ASSIGNED-OID
Description: LDAP Transaction Grouping Type
Person & email address to contact for further information:
Kurt Zeilenga <kurt@openldap.org>
Usage: Grouping
Specification: RFCxxxx
Author/Change Controller: IESG
Comments: none
7. Acknowledgments
The author gratefully acknowledges the contributions made by members
of the Internet Engineering Task Force.
8. Author's Address
Kurt D. Zeilenga
OpenLDAP Foundation
<Kurt@OpenLDAP.org>
9. Normative References
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[RFC2119] S. Bradner, "Key Words for use in RFCs to Indicate
Requirement Levels", BCP 14 (also RFC 2119), March 1997.
[RFC2251] M. Wahl, S. Kille, T. Howes, "Lightweight Directory Access
Protocol (v3)", RFC 2251, December 1997.
[RFC3377] J. Hodges, R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377, September 2002.
[GROUP] K. Zeilenga, "LDAP: Grouping of Related Operations",
draft-zeilenga-ldap-grouping-xx.txt, a work in progress.
[X.680] ITU-T, "Abstract Syntax Notation One (ASN.1) - Specification
of Basic Notation", X.680, 1994.
[X.690] ITU-T, "Specification of ASN.1 encoding rules: Basic,
Canonical, and Distinguished Encoding Rules", X.690, 1994.
10. Informative References
[ACID] Section 4 of ISO/IEC 10026-1:1992.
[RFC3383] K. Zeilenga, "IANA Considerations for LDAP", BCP 64 (also
RFC 3383), September 2002.
[X.500] ITU-T, "The Directory: Overview of Concepts, Models, and
Services", X.500, 1993.
[X.501] ITU-T, "The Directory: Models", X.501, 1993.
Copyright 2003, The Internet Society. All Rights Reserved.
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