Formal Specification and Optimization of ETL Workflows
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Transcript Formal Specification and Optimization of ETL Workflows
Data Provenance in ETL Scenarios
Panos Vassiliadis
University of Ioannina
(joint work with Alkis Simitsis, IBM Almaden Research Center,
Timos Sellis and Dimitrios Skoutas, NTUA & ICCS)
Outline
Introduction
Conceptual Level
Logical Level
Physical Level
Provenance &ETL
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Outline
Introduction
Conceptual Level
Logical Level
Physical Level
Provenance &ETL
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Data Warehouse Environment
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Extract-Transform-Load (ETL)
Extract
Sources
Transform
& Clean
Load
DSA
DW
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ETL: importance
ETL and Data Cleaning tools cost
ETL market: a multi-million market
IBM paid $1.1 billion dollars for Ascential
ETL tools in the market
30% of effort and expenses in the budget of the DW
55% of the total costs of DW runtime
80% of the development time in a DW project
software packages
in-house development
No standard, no common model
most vendors implement a core set of operators and provide GUI to
create a data flow
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Fundamental research question
Now: currently, ETL designers work directly at the
physical level (typically, via libraries of physicallevel templates)
Challenge: can we design ETL flows as declaratively
as possible?
Detail independence:
no care for the algorithmic choices
no care about the order of the transformations
(hopefully) no care for the details of the inter-attribute
mappings
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Now:
DW
Involved
data stores +
Physical
templates
Physical
scenario
Engine
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Vision:
Schema
mappings
ETL tool
Involved
data stores +
Conceptual to logical
mapping
Conceptual to
logical mapper
DW
DW
Physical
templates
Logical
templates
Logical
scenario
Optimizer
Physical
scenario
Physical
templates
Physical
scenario
Engine
Engine
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Detail independence
Schema
mappings
ETL tool
Automate
(as much as possible)
Conceptual: the
details of the interattribute mappings
Conceptual to logical
mapping
Conceptual to
logical mapper
Logical
templates
Logical
scenario
Optimizer
Logical: the order of
the transformations
Physical: the
algorithmic choices
DW
Physical
templates
Physical
scenario
Engine
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Outline
Introduction
Conceptual Level
Logical Level
Physical Level
Provenance &ETL
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Conceptual Model: first attempts
Necessary providers:
S1 and S2
Due to acccuracy
and small size
(< update window)
{Duration<4h}
PS1
U
Annual
PartSupp’s
PKey
DW.PARTSUPP
S2.PARTSUPP
Recent
PartSupp’s
PK
S1.PARTSUPP
SuppKey
{XOR}
Qty
PKey
PKey
SK
SuppKey
γ
Qty
Date
f
Cost
f
y
Ke
y
.P
Ke
2
S Supp
.
S2
S2.Date
SU
SU M(S2.Q
ty)
M
(S
2.
Co
st)
SK
SuppKey
Date
PKey
Dept
SuppKey
+
f
Qty
Qty
Cost
NN
Cost
Dept
$€
American to
European Date
PS2
Date = SysDate()
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PS1.Pkey+=PS2.PKey
PS1.SuppKey+=PS2.SuppKey
PS1.Dept+=PS2.Dept
PKey
SuppKey
Cost
Dept
12
Conceptual Model: The Data Mapping Diagram
Extension of UML to handle inter-attribute mappings
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Conceptual Model: The Data Mapping Diagram
Aggregating computes the quarterly sales for each product.
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Conceptual Model: Skoutas’ annotations
Application vocabulary
Datastore mappings
Datastore annotation
VC = {product, store}
VPproduct = {pid, pName, quantity, price,
type, storage}
VPstore = {sid, sName, city, street}
VFpid = {source_pid, dw_pid}
VFsid = {source_sid, dw_sid}
VFprice = {dollars, euros}
VTtype = {software, hardware}
VTcity = {paris, rome, athens}
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Conceptual Model: Skoutas’ annotations
The class hierarchy
Definition for class
DS1_Products
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Outline
Introduction
Conceptual Level
Logical Level
Physical Level
Provenance &ETL
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Logical Model
DS.PSNEW2.PKEY,
DS.PSOLD2.PKEY
SOURCE
DS.PSNEW2
DIFF2
DS.PS2
DS.PS1.PKEY,
LOOKUP_PS.SKEY,
SOURCE
AddAttr2
rejected
DS.PSOLD2
Log
DS.PS2.PKEY,
LOOKUP_PS.SKEY,
SOURCE
DS.PSNEW1.PKEY,
DS.PSOLD1.PKEY
DS.PSNEW1
DIFF1
DS.PS1
COST
SK2
rejected
A2EDate
$2€
rejected
rejected
Log
Log
COST
γ
Log
PKEY,DATE
U
AddDate
rejected
PK
rejected
DS.PSOLD1
Log
DSA
QTY,COST
rejected
DATE=SYSDATE
NotNULL
SK1
DATE
Log
Log
PKEY, DAY
MIN(COST)
S2.PARTS
FTP2
Aggregate1
DW.PARTS
DW.PARTSUPP.DATE,
DAY
S1.PARTS
PKEY, MONTH
AVG(COST)
FTP1
TIME
Sources
V1
Aggregate2
V2
DW
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Logical Model
Main question:
What information should we put inside a metadata
repository to be able to answer questions like:
what is the architecture of my DW back stage?
which attributes/tables are involved in the population of
an attribute?
what part of the scenario is affected if we delete an
attribute?
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Architecture Graph
DS.PSNEW2.PKEY,
DS.PSOLD2.PKEY
SOURCE
DS.PSNEW2
DIFF2
DS.PS2
DS.PS1.PKEY,
LOOKUP_PS.SKEY,
SOURCE
AddAttr2
rejected
DS.PSOLD2
Log
DS.PS2.PKEY,
LOOKUP_PS.SKEY,
SOURCE
DS.PSNEW1.PKEY,
DS.PSOLD1.PKEY
DS.PSNEW1
DIFF1
DS.PS1
COST
rejected
A2EDate
$2€
SK2
rejected
rejected
Log
Log
COST
γ
Log
PKEY,DATE
U
AddDate
rejected
PK
rejected
DS.PSOLD1
Log
DSA
QTY,COST
rejected
DATE=SYSDATE
NotNULL
SK1
DATE
Log
Log
PKEY, DAY
MIN(COST)
S2.PARTS
FTP2
Aggregate1
DW.PARTS
DW.PARTSUPP.DATE,
DAY
S1.PARTS
PKEY, MONTH
AVG(COST)
FTP1
TIME
Sources
V1
Aggregate2
V2
DW
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Architecture Graph
Example
DS.PS2
OUT
IN
Add_Attr2
OUT
IN
PAR
OUT
SK2
IN
PAR
PKEY
PKEY
PKEY
PKEY
PKEY
PKEY
SUPPKEY
SUPPKEY
SUPPKEY
SUPPKEY
SUPPKEY
SUPPKEY
QTY
QTY
QTY
QTY
QTY
QTY
COST
COST
COST
COST
COST
COST
DATE
DATE
DATE
DATE
DATE
DATE
SOURCE
SOURCE
SOURCE
SOURCE
SKEY
AddConst2
in
TMP_STOR.
PARTSUPP
PKEY
out
SOURCE
1
2
LOOKUP2
OUT
PKEY
LPKEY
SOURCE
LSOURCE
SKEY
LSKEY
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Architecture Graph
Example
DS.PS2
OUT
IN
Add_Attr2
OUT
input
schema
PAR
IN
OUT
SK2
IN
output
schema
PAR
PKEY
PKEY
PKEY
PKEY
PKEY
PKEY
SUPPKEY
SUPPKEY
SUPPKEY
SUPPKEY
SUPPKEY
SUPPKEY
QTY
QTY
QTY
QTY
QTY
QTY
COST
COST
COST
COST
COST
COST
DATE
DATE
DATE
DATE
DATE
DATE
SOURCE
SOURCE
SOURCE
SOURCE
SKEY
AddConst2
in
TMP_STOR.
PARTSUPP
PKEY
out
SOURCE
1
2
LOOKUP2
OUT
PKEY
LPKEY
SOURCE
LSOURCE
SKEY
LSKEY
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projected-out
schema
generated
schema
functionality
schema
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Optimization
Execution order…
S2.PARTSUPP
PKey
DW.PARTSUPP
PKey
SK
SuppKey
γ
Qty
Date
f1
Cost
f2
PK
y
Ke
P
.
y
S2
pKe
Sup
.
2
S
S2.Date
SUM
SU (S2.Q
ty)
M(
S2
.C
os
t)
SuppKey
Date
Qty
Cost
which is the proper
execution order?
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Optimization
Execution order…
S2.PART
SUPP
SK
f1
γ
f2
PK
DW.PART
SUPP
order equivalence?
SK,f1,f2 or SK,f2,f1 or ... ?
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Logical Optimization
1
PARTS1
2
PARTS2
3
7
NN
8
9
σ
U
(€COST)
4
5
$2€
A2E
($COST)
(DATE)
6
γ(DATE)
1
8_1
PARTS1
σ(€COST)
3
NN
(€COST)
7
U
2
PARTS2
4
8_2
$2€
σ
($COST)
(€COST)
Can we push selection
early enough?
Can we aggregate
before $2€ takes place?
PARTS
(€COST)
6
γ(DATE)
9
PARTS
5
A2E
(DATE)
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Outline
Introduction
Conceptual Level
Logical Level
Physical Level
Provenance &ETL
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Logical to Physical
ETL tool
Schema
mappings
Conceptual to
logical mapper
Conceptual to logical
mapping
Logical
templates
Logical
scenario
Optimizer
Physical
templates
DW
Physical
scenario
“identify the best
possible physical
implementation for a
given logical ETL
workflow”
Engine
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Problem formulation
Given
a logical-level ETL workflow GL
Compute a physical-level ETL workflow GP
Such that
the semantics of the workflow do not change
all constraints are met
the cost is minimal
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Solution
We model the problem of finding the physical implementation of an ETL
process as a state-space search problem.
States. A state is a graph GP that represents a physical-level ETL workflow.
Transitions. Given a state GP, a new state GP’ is generated by replacing the
implementation of a physical activity aP of GP with another valid
implementation for the same activity.
The initial state G0P is produced after the random assignment of physical
implementations to logical activities w.r.t. preconditions and constraints.
Extension: introduction of a sorter activity (at the physical-level) as a new
node in the graph.
Sorter introduction
Intentionally introduce sorters to reduce execution & resumption costs
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Sorters: impact
We intentionally introduce orderings, (via appropriate physical-level sorter
activities) towards obtaining physical plans of lower cost.
Semantics: unaffected
Price to pay:
cost of sorting the stream of processed data
Gain:
it is possible to employ order-aware algorithms that significantly reduce
processing cost
It is possible to amortize the cost over activities that utilize common useful
orderings
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Sorter gains
3
500
γA
100000
R
σA<600
sel3=0.1
2
1
10000
sel1=0.1
Z
5000
σA>300
sel2=0.5
4 1000
V
γA,Β
W
sel4=0.2
5
1000
γB
Y
sel5=0.2
Without order
cost(σi) = n
costSO(γ) = n*log2(n)+n
With appropriate order
cost(σi) = seli * n
costSO(γ) = n
Cost(G) = 100.000+10.000
+3*[5.000*log2(5.000)+5.000] = 309.316
If sorter SA,B is added to V:
Cost(G’) = 100.000+10.000
+2*5.000+[5.000*log2(5.000)+5.000] =
247.877
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Interesting orders
3
500
γA
100000
R
sel3=0.1
2
1
10000
σA<600
sel1=0.1
Z
5000
σA>300
4 1000
V
γA,Β
sel2=0.5
W
sel4=0.2
5
A asc
A desc
{A,B, [A,B]}
1000
γB
Y
sel5=0.2
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Outline
Introduction
Conceptual Level
Logical Level
Physical Level
Provenance &ETL
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A principled architecture for ETL
ETL tool
Schema
mappings
Conceptual to
logical mapper
Conceptual to logical
mapping
Logical
templates
DW
WHY
Logical
scenario
WHAT
Optimizer
Physical
templates
Physical
scenario
HOW
Engine
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Logical Model: Questions revisited
What information should we put inside a metadata
repository to be able to answer questions like:
what is the architecture of my DW back stage?
it is described as the Architecture Graph
which attributes/tables are involved in the population of
an attribute?
what part of the scenario is affected if we delete an
attribute?
follow the appropriate path in the Architecture Graph
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Fundamental questions on provenance & ETL
Why do we have a certain record in the DW?
Because there is a process (described by the Architecture
Graph at the logical level + the conceptual model) that
produces this kind of tuples
Where did this record come from in my DW?
Hard! If there is a way to derive an “inverse” workflow
that links the DW tuples to their sources you can answer
it.
Not always possible: transformations are not invertible,
and a DW is supposed to progressively summarize data…
Widom’s work on record lineage…
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Fundamental questions on provenance & ETL
How are updates to the sources managed?
(update takes place at the source, DW+data marts must be
updated)
Done, although in a tedious way: log sniffing, mainly.
Also, “diff” comparison of extracted snapshots
When errors are discovered during the ETL process,
how are they handled?
(update takes place at the data staging area, sources must
be updated)
Too hard to “back-fuse” data into the sources, both for
political and workload issues. Currently, this is not
automated.
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Fundamental questions on provenance & ETL
What happens if there are updates to the schema of
the involved data sources?
What happens if we must update the workflow
structure and semantics?
Currently this is not automated, although the automation
of the task is part of the detail independence vision
Nothing is versioned back – still, not really any user
requests for this to be supported
What is the equivalent of citations in ETL?
… nothing really …
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Thank you!
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