Contest of XML Lock Protocols

© 2006 AG DBIS

VLDB2006

Contest of XML Lock ProtocolsContest of XML Lock Protocols

32nd Int. Conf. on Very Large Data Bases32nd Int. Conf. on Very Large Data BasesVLDB 2006VLDB 200612-15 September 2006, Seoul, Korea12-15 September 2006, Seoul, Korea

Michael P. Haustein, SAP AG Theo Härder, Univ. of Kaiserslautern

Konstantin Luttenberger, Fraunhofer Institute IESE

[email protected]

mailto:[email protected]

http://www.uni-kl.de/AG-Haerder

2© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group

Performanceevaluation

Conclusionsand outlook

Introductionto XTC

Introduction

OutlineOutline Key ideas of 2 groups of competing XML lock

protocols• Doc2PL and followers

- Node2PL, NO2PL, OO2PL• multi-granularity locking (MGL* group)

- RIX, RIX+, IRIX, IRIX+, URIX

Our own protocols: taDOM group• taDOM2: base protocol for DOM2• lock conversion• optimization to taDOM2+• not considered taDOM3, taDOM3+

Introduction to XTC• identifying nodes• meta-synchronization

Performance evaluation• taMIX framework• transaction types of the Banking benchmark• measurements and comparison

Conclusions and outlook


3© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

DOM Storage ModelDOM Storage Model XML document

<?xml version="1.0"?><bib> <book year="2004" id="book1"> <title>The Title</title> <author> <last>Lastname</last> <first>Firstname</first> </author> <price>49.99</price> </book></bib>

• NavigationgetFirst/LastChildgetNextSiblinggetPreviousSiblinggetAttributes/Value

• ModificationappendChildinsertBeforeremoveChild

• QuerygetElementByIdgetChildNodes

DOM API (> 20 ops)

T

bib

book

title author priceid year

Tlast first

TTThe Title

Lastname

Firstname

49.99

book1 2004

element node

attribute nodetext node


4© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Doc2PL and its FollowersDoc2PL and its Followers Basic assumption: Traversal

from root to context node

Sample of operations• nthP retrieves the nth child

of C• nthM retrieves the nth child

(backw.)• insA inserts a new node

after C • insB inserts a new node

before C• del deletes a given node

Separation of traversal and modification of• document structure (T/M)• content (S/X)• direct jumps (IDR/IDX)• no intention locks!

0. Doc2PL only locks roots

1. Node2PL acquires locks for parent nodes

root

context node C

lock modes:

Structural navigation to locate an object often implies ako document scan repeatable read requires T locks on all nodes

content + structure S X T M

S + - + -X - - + -T + + + -M - - - -

T

M parent P

entire child axis of P affected


5© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Doc2PL and its Followers (2)Doc2PL and its Followers (2)2. NO2PL

• acquires locks for all nodes whose (conceptual) pointers are traversed or modified

example at C1: insB (C0)

3. OO2PL • locks (conceptual) pointers

for every node- A/Z: first/last child- R/L: next/previous sibling

example: del C2

only context node and selected child nodes affected

root

…C1

P

Cn

+-+++-++MA++-+++-+MR+++-+++-ML-+++++++TZ+-++++++TA++-+++++TR+++-++++TL

MZMAMRMLTZTATRTL

-+++-+++MZ

T

M

M

C0

root

C1

P

C3C2

ML

T

TA

MR

TZ

Increasing degree of concurrency:Doc2PL -> Node2PL -> NO2PL -> OO2PL


6© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Making Full-Fledged Protocols for the *-2PL Making Full-Fledged Protocols for the *-2PL GroupGroup

M

T

T T

Tidref

IDS

rootrootT

What’s about IDREF(S) links? –

T T

id

T T

T

T T

T

id

IDX IDS

Idea of T/M lock modes - requires non-interrupted path traversal - prohibits indexed document access: how to protect the ancestor path in case of direct jumps?

A single lock on the jump target is only sufficient for read ops!

(Very expensive) solution for the *-2PL group:node deletion requires IDX locks on all descendents having ID attr.

IDX

locks for direct jumps (IDS/IDX) needed!


7© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

What Else Do Full-Fledged XML Protocols What Else Do Full-Fledged XML Protocols Need?Need? Support of direct access via indexes

• jumps to element nodes not owning an ID attribute• cheap mechanism to identify the ancestor node IDs!

Lock conversion• operations of a transaction necessarily share some part

of the ancestor path • weakest possible locks after conversion

Appropriate intention locks and subtree locks needed• lock depth parameter desirable

Use ideas of MGL locking • subtree locks + intention locks• 4. IRX

• 5. IRX+- specialized conversion (+)- depending on locking situation

- I R XI + + - -R + - + -X + - - -

compatibility matrix- I R X

I I I X XR R X R XX X X X X

conversion matrix

- I R XI I I R/X XR R R/X R XX X X X X

conversion matrix


8© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Applying Multi-Granularity Locking to XMLApplying Multi-Granularity Locking to XML 6. IRIX conversion

• read C1 – C3

• delete C2

7. IRIX+ specialized conversion

• read C1 – C3

• delete C2

root

C1

P

C3C2

IR

R

root

C1

P

C3C2

IX

X

- IR IX R XIR IR IR IX R XIX IX IX IX IXR XR R R IXR R XX X X X X X

root

C1

P

C3C2

IR

R

root

C1

P

C3C2

IX

IX

XR R

- IR IX R XIR IR IR IX R XIX IX IX IX X XR R R X R XX X X X X X


9© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

MGL Group (Cont.)MGL Group (Cont.)

8. URIX • compatibility matrix

• conversion matrix

read for update C1 – C3

delete C2

- IR IX R RIX U XIR + + + + + - -IX + + + - - - -R + + - + - - -

RIX + + - - - - -U + + - + - - -X + - - - - - -

- IR IX R RIX U XIR IR IR IX R RIX U XIX IX IX IX RIX RIX X XR R R RIX R RIX R X

RIX RIX RIX RIX RIX RIX X XU U U X U X U XX X X X X X X X

root

C1

P

C3C2

IX

RIX

X

root

C1

P

C3C2

IX

RIX

U


10© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Tailored Node LocksTailored Node Locks for XML – for XML – taDOM2taDOM2 9. taDOM2 Node locks and compatibility matrix

• refined URIX protocol with extensions to lock a complete level in a subtree

- well known: IR/IX and R/X (here SR/SX)• edge locks not discussed (3 modes)

lock effectIR intention read lock on a

nodeNR (node read) locks only a context nodeLR (level read) read lock on a context node

and all direct-child nodesSR (subtree read)

read lock on an entire subtree

lock effectIX (intent. excl.) intention of a write lock on a

non-direct child nodeX (exclusive) write lock on an entire subtreeCX (child excl.) indicates existence of a write

lock on a direct child nodeSU (update option)

read lock for intended update operations on an entire subtree

- IR NR LR SR IX CX U XIR + + + + + + + - -NR + + + + + + + - -LR + + + + + + - - -SR + + + + + - - - -IX + + + + - + + - -CX + + + - - + + - -SU + + + + + - - - -SX + - - - - - - - -

Read locks

Write locks

Compatibility matrix


11© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Node Locks (1)Node Locks (1) Node read lock (NR)

• requires IR locks on the ancestor path Level read lock (LR)

• requested for reading the context node and all nodes located at the level below (all direct-child nodes)

Child exclusive lock (CX)• indicates an X lock on a child• defined, in addition to IX, to detect conflicts with

LR

T

bib

book

title author price

Tlast first

TTThe Title

Lastname

Firstname

49.99

Transaction T1 is reading <price> IR

IR

NRTransaction T2 is reading <book>and all direct-child nodes(<title>, <author>, and <price>)

LR

IR

Transaction T3 is modifyingthe book title

IX

IX

IX

CXX


12© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Node Locks (2)Node Locks (2) Locking subtrees exclusively: intention exclusive lock

(IX), child exclusive lock (CX), and exclusive lock (X)• requested for updating the context node's content or

deleting the context node and its entire subtree• requires a CX lock on the parent and IX locks on the

ancestors

T

bib

book

title author price

Tlast first

TTThe Title

Lastname Firstname

49.99

Transaction T1 is deleting the<first> node and its content

X

CX

IX

IXTransaction T2 is deleting the<last> node and its content

X

CX

IX

IX

Transaction T4 is reading alldirect-child nodes of <book>

LR

IR

but is blocked when readingall child nodes of <author>

LR

Transaction T3 is reading the<author> node

IR

IR

NR


13© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Tunable Lock DepthTunable Lock Depth Goal

• reduce the number of locks held by usingcoarser lock granularity

• may decrease concurrency• when nodes deeper than lock depth are accessed:

lock modes SR and X are used at the lock depth level

T

bib

book

title author price

Tlast first

TTThe Title

Lastname Firstname

49.99

Transaction T1 is readingthe author's last name

NRIR

IR

IR

IR

IR

SR

Transaction T2 is updatingthe author's first name

XCX

IX

IX

IX

IX

CX

Xlock depth 2however, using

Transaction T1 would have to acquire an SR lock on author

Transaction T2 would have toacquire an X lock on authorand would therefore have towait on author


14© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Conversion of Node LocksConversion of Node Locks Conversion for weakest possible locking paths

• LR CX requires explicit NR locks on all children • node labeling scheme cannot deliver IDs of descendent nodes

conversion matrix

T

bib

book

title author price

Tlast first

TTThe Title

Lastname

Firstname

49.99

Transaction T1 is reading <book>and all its direct-child nodes

IR

LR

Transaction T2 is reading <book>,the first child node <title> and its value

NR

IR

NRNR

NR

Transaction T1 is deleting <author>and its entire subtree

X

CX

NR NR

IX - IR NR

LR SR IX CX SU SX

IR IR IR NR

LR SR IX CX SU SX

NR NR

NR

NR

LR SR IX CX SU SX

LR LR LR LR LR SR IXNR CXN

R

SU SX

SR SR SR SR SR SR IXSR CXSR SR SXIX IX IX IX IXNR IXSR IX CX SX SXCX CX CX CX CXNR CXNR CX CX SX SXSU SU SU SU SU SU SX SX SU SXSX SX SX SX SX SX SX SX SX SX

CXNR

IX


15© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

taDOM* Group – Lock Protocol taDOM* Group – Lock Protocol OptimizationOptimization 10. taDOM2+: LRIX, SRIX, LRCX, SRCX

• new lock modes enable conversion without accessing the document

• e.g., LRCX (level read child exclusive) combines both modes and avoids application of conversion rule CXNR

Optimization steps• 11. taDOM3: modification of a single context node• 12. taDOM3+: new lock modes to avoid document

access

SXSXSXSXSXSXSXSXSXSXSXSXSXSX

SXSUSXSUSXSXSXSXSUSUSUSUSUSU

SXSXNXNXNXNXNXNXNXSRNXNRNXNXNXNX

SXSUNXNUNXNXNXNXNUSRNUNRNUNUNUNU

SXSXNXNXNRCXNRCXNRCXNRCXNRCXSRNRCXNRNRCXNRCXNRCXNRCX

SXSXNXNXNRCXCXNRCXCXNRCXSRNRCXNRNRCXCXCXCX

SXSXNXNXNRCXNRCXNRIXNRIXNRIXSRNRIXNRNRIXNRIXNRIXNRIX

SXSXNXNXNRCXCXNRIXIXNRIXSRNRIXNRNRIXIXIXIX

SXSRNXSRNUSRNRCXSRNRCXSRNRIXSRNRIXSRSRSRSRSRSRSR

SXSUNXNRNUNRNRCXNRNRCXNRNRIXNRNRIXNRSRLRLRLRLRLR

SXSUNXNRNRCXNRCXNRIXNRIXSRLRNRNRNRNR

SXSUNXNUNRCXCXNRIXIXSRLRNRIRIRIR

SXSUNXNUNRCXCXNRIXIXSRLRNRIR-

Example: lock conversion in taDOM3


16© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

XTC – Architectural OverviewXTC – Architectural Overview

determination of ancestor node IDs are of outmost importance for any locking protocol

OS File SystemTransaction Log Container Files Temporary Files

XTCs

erve

r

Transaction Services

File Services

Propagation Control

Access Services

Node ProcessingServices

XML Processing Services

Interface ServicesHttp Agent Ftp Agent DOM RMI SAX RMI API RMI

XML Manager XSLT ProcessorXQuery Processor

Node Manager

Record Mgr Index Mgr Catalog Mgr

Buffer Manager

I/O Manager Temp File Mgr

Transaction Manager

Lock Manager

Deadlock Detector

Path Processing

L1

L2

L3

L4

L5


17© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

taDOM Storage Model – View of Lock taDOM Storage Model – View of Lock MgrMgr XML document

<?xml version="1.0"?><bib> <book year="2004" id="book1"> <title>The Title</title> <author> <last>Lastname</last> <first>Firstname</first> </author> <price>49.99</price> </book></bib>

string node

T

bib

book

title author price

id year Tlast first

TTThe Title

Lastname

Firstname

49.99book1 2004

attribute root node

element node

attribute node text node


18© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Identifying Nodes – Node Numbering Identifying Nodes – Node Numbering SchemesSchemes

T

bib

book

title author priceid

year

Tlast first

TTThe Title

Lastname

Firstname

49.99book1

2004

1

32

45

67

89

10

11

12

1314

15

1617

1819

20new

21

new1.3.5.4.3

sequential

- very slow, although supported by on-demand indexes- determination of parent ID and ancestor IDs, however, is very frequent

1.3.1.3.1 1.3.5.3.3.1 1.3.5.5.3.1

1.3.1.1

1

1.3

1.3.1 1.3.3 1.3.5 1.3.7

1.3.1.3

T

bib

book

title author price

id

year

Tlast first

TT

The Title

Lastname

Firstname

49.99book1

2004

1.3.1.1.11.3.3.3

1.3.3.3.1

1.3.5.3

1.3.5.3.3

1.3.5.5

1.3.5.5.3

1.3.7.3

1.3.7.3.1

SPLIDs (DeweysIDs)


19© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Meta-SynchronizationMeta-Synchronization Meta-synchronization

• allows identical runtime environment for lock contests• lock mgr provides methods: supportsSharedLevelLocking,

supportsSharedTreeLocking, supportsExclusiveTreeLocking

Meta-lock requests from node manager to lock manager• request shared node lock • request shared level lock• request tree lock (shared, update, exclusive)• . . .

Meta-lock requests are mapped to the actual lock algorithm• lock manager implements a certain interface• exchange of the lock manager interface implementation

exchanges the system's complete XML locking mechanism

Advantages of SPLIDs used in all 12 protocols!


20© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

TaMix Benchmark FrameworkTaMix Benchmark Framework So far, no update benchmark for XML docs available

• TaMix infrastructure for distributed OLTP benchmarks

• a list of TX types is assigned to each client • each client runs n TX in parallel and keeps the workload

level Automated measurement

• per measurement point 3 runs• configurable runtime interval• for 12 lock protocols• in 6 lock depths ~ 20 hours per measurement

server

Coordinator

XTC Serverstart / stop

configuration

nodeClient

nodeClient

nodeClient


21© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Data base (DataGuide)

Size• ~8 MB • 580,000 taDOM nodes

Bank

Customers Accounts

Customer

id

Address

Street No Zip City

Name

Fname Name

Account

id OwnerBalance Credit

Standing_OrdersProtocols Postings

Protocol Posting

Standing_Order

Day Receiver AccountNo ABA_No Amount Disposition

Performance Measurement Performance Measurement


22© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Transaction types for Banking benchmark• bank transfer (5 TX/client)

- jump to a randomly selected account element- navigation through the document, update operations for Balance and

Posting• standing order (5 TX/client)

- random account, navigation to Standing Orders, read of all orders- evaluation of the Child axis, small fraction of update operations

• customer master- renaming of a Customer element (1 TX/client)- in parallel, reconstruction of randomly selected Customer fragments (5

TX/client)• account statement (5 TX/client)

- reconstruction of randomly selected Account fragments- small amount of update operations (insertion an entry in Protocols)

• removal of a customer from the data base (2 TX/client)- deletion of fragments

Transaction mix • processes all transaction types in parallel• constant system load of 66 transactions

Performance Measurement (2)Performance Measurement (2)


23© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Performance Measurement Performance Measurement (3)(3) Number of committed transactions in Banking

benchmark

100

150

200

250

300

350

400

0 1 2 3 4 5

taDOM3+, taDOM2+

taDOM3, taDOM2

URIX

RIX(+), IRIX(+)

Node2PL, NO2PL, OO2PL

lock protocol taDOM3+ taDOM3 taDOM2+ taDOM2 URIX IRIX IRIX+ RIX RIX+ OO2PL NO2PL Node2PL

lock depth


24© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Number of aborted transactions in Banking benchmark

0

100

200

300

400

500

600

700

0 1 2 3 4 5

RIX(+), IRIX(+)

taDOM, URIX



Performance Measurement Performance Measurement (4)(4)

lock depth


25© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Successful bank transfers node-based navigation, update operations

Detailed Performance Measurement Detailed Performance Measurement (5)(5)

0

50

100

150

200

250

300

350

400

0 1 2 3 4 5


taDOM,URIX

RIX(+), IRIX(+)

taDOM2, taDOM3


lock depth


26© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Successfully modified standing orders evaluation of child axis, few update operations


0

100

200

300

400

500

600

700

800

0 1 2 3 4 5

taDOM3+, taDOM2+

taDOM3, taDOM2

MGLNode2PL, NO2PL, OO2PL

taDOM,URIX

RIX(+), IRIX(+)


lock depth


27© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Customer Master: successfully modified Customer elements + reconstructed Customer fragments renaming of an inner element node


800

900

1000

1100

1200

1300

1400

1500

0 1 2 3 4 5

taDOM

URIX

RIX(+), IRIX(+)



lock depth


28© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Successfully processed account statements reconstruction of fragments, few update operations


0

100

200

300

400

500

600

700

800

0 1 2 3 4 5

taDOM, MGL



lock depth


29© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Successfully removed customer records deletion of fragments


0

20

40

60

80

100

120

140

0 1 2 3 4 5

RIX(+), IRIX(+)

taDOM,URIX

NO2PL, OO2PL

taDOM, MGL

Node2PL


lock depth


30© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Conclusions and OutlookConclusions and Outlook XTC is used as a test vehicle for empirical DB research

• effectiveness of XML concurrency control- fine-granular locking on nodes and edges- meta-synchronization allows comparison of different

compatibilities- taDOM* protocols

multiplicity of lock modes intention locks are important indexed document access is frequent ancestor path locking without accessing the storage engine desirable

• performance evaluation revealed- use of tailored lock modes pays off- indexed document access is frequent- effect of isolation levels on transaction throughput - influence of node numbering schemes (insertions at arbitrary

positions)

Outlook• phantom prevention• mapping different XML language models via access models

to our XML storage model, e. g., to analyze the locking behavior of XQuery processing


31© 2006 AG DBIS

VLDB2006

MGL* group

*-2PL group

taDOM*group



Introductionto XTC

Introduction

Thank you. Any questions?

Contest of XML Lock ProtocolsContest of XML Lock Protocols


Contest of XML Lock Protocols

Documents

t locks

idx locks

no2placquires locks

locks roots

new node

node deletion

ancestor node ids

irix conversion