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Lock-Free Consistency Control for Web 2.0 Applications. Jiang-Ming Yang, Hai-Xun Wang, Ning Gu, Yi-Ming Liu, Chun-Song Wang, Qi-Wei Zhang 25 April 2008. Outline. Motivation & Challenges Problem Setting Our Solutions Experiments Conclusions. Outline. Motivation & Challenges

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Lock free consistency control for web 2 0 applications

Lock-Free Consistency Control for Web 2.0 Applications

Jiang-Ming Yang, Hai-Xun Wang, Ning Gu, Yi-Ming Liu, Chun-Song Wang, Qi-Wei Zhang

25 April 2008


Outline
Outline

  • Motivation & Challenges

  • Problem Setting

  • Our Solutions

  • Experiments

  • Conclusions


Outline1
Outline

  • Motivation & Challenges

  • Problem Setting

  • Our Solutions

  • Experiments

  • Conclusions


Motivation
Motivation

  • Single Site


Motivation1
Motivation

  • Multiple Mirror Site


Challenges
Challenges

  • How to merge the conflicts in Multiple Mirror Site for Web 2.0 Application?

?

?


Outline2
Outline

  • Motivation & Challenges

  • Problem Setting

  • Our Solutions

  • Experiments

  • Conclusions


Problem setting
Problem Setting

  • Data shared in mirrored sites can be in varied forms. Here, we assume the shared data on mirrored sites are XML documents.

  • Consequently, operations on the data are expressed by XML queries and updates.


Problem setting1
Problem Setting

<Root>

<book @title="Introduction to Algorithm">

<category>CS</category>

<tag>Hot</tag>

</book>

<book @title="Advanced Statistical Learning">

<category>UnKnow</category>

</book>

<book @title="Linear Algebra">

<category>Math</category>

</book>

</Root>


Problem setting2
Problem Setting

  • CAUSAL RELATIONSHIPS

  • TRANSACTIONS

  • CONCURRENT OPERATIONS (Lock Free)


Problem setting3
Problem Setting

  • CAUSAL RELATIONSHIPS

    U1

    Change the title “Advanced Statistical Learning” to “Statistical Learning”.

    U2

    Set the category of the “Statistical Learning” book to “Math”.


Problem setting4
Problem Setting

  • TRANSACTIONS

    • Using transaction model to execute some critical operations

    • Should be executed serialized with others


Problem setting5
Problem Setting

  • CONCURRENT OPERATIONS

    U3

    Add a “Discount” tag to books in “Math” category.

    U4

    Set the category of the “Linear Algebra” book to “CS”.


Outline3
Outline

  • Motivation & Challenges

  • Problem Setting

  • Our Solutions

    • Causality Preservation

    • Transaction

    • Consistency Control

  • Experiments

  • Conclusions


Causality preservation
Causality Preservation

  • Definition. (Causal Ordering Relation “→”). Given two operations Oa and Ob from local replica sites i and j respectively, we have Oa → Ob, if and only if (1) i = j, and Oa is generated before Ob is generated; (2) i ≠ j, and Oa is executed on site j before Obis generated; (3) there exists an operation Ox, such that Oa → Oxand Ox → Ob.

  • Definition.(Concurrent Relation “ ”). Given two operations Oa and Ob, we say Oa and Ob are concurrent or Oa Ob iff neither Oa → Ob, nor Ob → Oa.


Causality preservation1
Causality Preservation

  • Vector based Timestamp

    • SV = <SV1, SV2, . . . , SVn>

    • Both for Site & operation

  • Definition. (Execution Condition).Operation O (from site i) is causally ready for execution at site j (i ≠ j) if the following conditions are satisfied: (in reference [6, 14])

    • SVO[i] = SVj[i] + 1

    • SVO[k] ≤ SVj[k], for all 1 ≤ k ≤ N and k ≠ i.


Transaction
Transaction

  • The transaction model is introduced to achieve concurrent transparency

  • Definition. (Serialized Transaction). Let T be a transaction, and O be an operation (O may or may not be a transaction). Transaction T is a serialized transaction only if either O is executed before T in all sites, or O is executed after T in all sites.


Transaction1
Transaction

  • O1 → NOOP1 → O3 and O2 → NOOP2 → O4


Transaction2
Transaction

  • Definition. (TOrder: total order for transactions). It’s a logical order among transactions : T1 ≺ T2 ≺ T3 ≺ … ≺ Tn.


Consistency control basic idea
Consistency Control – Basic Idea


Consistency control operation
Consistency Control - Operation

  • XPath : /root/book

  • XQuery & XUpdate

    FOR $title in /root//title

    $category = $book/category

    WHERE $title = "Advanced Statistical Learning"

    ..


Consistency control storage model
Consistency Control– Storage Model


Consistency control storage model1
Consistency Control– Storage Model


Consistency control storage model2
ConsistencyControl–StorageModel


Consistency control query process
Consistency Control- Query Process

  • It is clear that there is no overlap in their timestamps, and at any time only one of them is valid.

  • In general, only nodes whose timestamp (tcreate, tdelete) satisfies t ∈ (tcreate, tdelete) are valid at t.


Consistency control query process1
Consistency Control- Query Process


Consistency control size of ohl
Consistency Control – Size of OHL

  • In our approach, we store operations in an Operation History List (OHL).

  • Each time a replica receives a new remote operation, it will update OHL.

  • When an operation is executed on all replicas, it will be removed from OHL and its related state information will be removed from the inverted list.


Outline4
Outline

  • Motivation & Challenges

  • Problem Setting

  • Our Solutions

  • Experiments

  • Conclusions





Outline5
Outline

  • Motivation & Challenges

  • Problem Setting

  • Our Solutions

  • Experiments

  • Conclusions


Conclusions
Conclusions

  • We proposed a lock-free approach for consistency maintance in Web 2.0 environment.

    • We do not use the locking mechanism, so concurrent operations are executed as soon as possible upon their arrival with ensuring the convergence.

    • We also support the transaction semantics for critical operations without using the locking mechanism relying on the causality preservation approach.

    • Better load balance, high-speed access and shorter respond time



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