Sandeep Hans Agenda Database Consistency Conditions STM Consistency Conditions A different perspective Consistency with other STM properties Conclusion Database Consistency Conditions Recoverability ID: 198794
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Slide1
Consistency Conditions for STM
Sandeep
HansSlide2
Agenda
Database Consistency Conditions
STM Consistency Conditions
A different perspective
Consistency with other STM properties.
ConclusionSlide3
Database Consistency Conditions
Recoverability
Avoiding Cascading Aborts
Strictness
RigorousnessSlide4
Dirty Reads
T
1
writes
x
.
T
2 reads x written by T1 .T2 commits, T1 aborts.
T
1
w1(x)
a
r
2(x)
c2
T2Slide5
Recoverability
T
1
writes
x
.
T
2 reads x written by T1 .T1 should commit before T2 commits.
T
1
w
1(x)
c1
r
2(x)
c2
T
2Slide6
Problem with Recoverability
Cascading aborts
T
1
w
1
(x)
r
2
(x)
T
2
c
1
c
2
a
1
a
2Slide7
Avoiding Cascading Aborts
T
1
should commit before
T
2
commits reads x.
T1
w1(x)
c1
r
2
(x)c
2T2Slide8
Undo Problem
Initially, x=1.
T
1
writes
x=2
.
T2 writes x=3 and commits.T1 aborts.
T
1
w1(x=2)
a1
w
2(x=3)
c2
T2Slide9
Strictness
No data item is read or overwritten unless the transaction that wrote it has ended.
T
1
w
1
(x)
c
1
/a
1
r
2(x)
T2
w3
(x)T3Slide10
Rigorousness
No data item is read or overwritten unless the transaction that read/wrote it has ended.
T
1
w
1
(x)
c
1
/a
1
r
2(x)
T2
w
3(x)T3
c
2
/a
2Slide11
Landscape
RG
ST
ACA
RC
[
Transactional Information Systems.
Gerhard
Weikum
, Gottfried
Vossen
.]Slide12
STM Conditions
Opacity
Guerraoui
and
Kapalka
[
PPoPP’08]Sequential specification of shared objects.Virtual World ConsistencyImbs and Raynal [SIROCCO’09] Causal past of a transaction.
Weakest Reasonable ConditionDoherty , Groves, Luchangco, Moir
[REFINE’09] Slide13
Database vs.
STM
Rigorousness ⊆
Opacity
⊂
Strictness
Rigorousness ⊆
VWC ⊂ Strictness
⊆
⊆
Are
these inclusions strict?Slide14
Another Perspective
How do we view the system?
Operation level.
Database
consistency conditions.
Recoverability, ACA, Strictness, Rigorousness
Transaction level.
STM consistency conditions.Opacity, VWCIs there another level?Slide15
Snapshot Isolation
Everyone
will have a snapshot of the whole system.
A snapshot must be consistent at every point of time.
Different snapshots need not be consistent with each other.
Updating of snapshots is allowed.Slide16
How consistency conditions
affect STM properties.
DAP + Invisible Reads + Wait-free +
Serializability
= Impossible.
1
We have seen the proof on Wednesday.
How do Opacity/VWC affect such results.DAP + Wait-free + VWC = possible?DAP + Wait-free + Opacity = impossible?
1. Hagit
Attiya, Eshcar Hillel,
Alessia
Milani
.
Inherent Limitations on
Disjoint-Access Parallel Transactional Memory. SPAA 2009. Slide17
Conclusion
Motivation for database and STM consistency conditions is same yet perspectives differ.
STM consistency conditions affect other properties.Slide18
Thank You