Lock free consistency control for web 2 0 applications
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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

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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


Experiments

Experiments


Experiments1

Experiments


Experiments2

Experiments


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


Thank you

Thank You !


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