graceful database schema evolution: the prism workbench

Graceful Database Schema Evolution:

the PRISM Workbench

Carlo A. Curino, Hyun J. Moon, and Carlo Zaniolo

VLDB 2008

Presented by: Kristian Torp

Database Specialization Course 2010 2

Motivation

• Problems select * from emp insert into emp (name, dept) values (:x, :y)

• Current status Manual, error prone, time-consuming process Missing methods and tools

Name Dept

Jens HR

Lone RD

Name Dept Salary

Jens HR 10

Lone RD 20

Version n Version n+1

New requirements

“Database Refactoring”

Overview• Challenges• Schema Modification Operators (SMOs)• The tool and performance• Conclusion• Critique


The Current Situation and Solution


v1

v2

Time

“Rock Climbing”

v1 v2 v3 v4 v5

Time

“Stepping Stones”

forwardbackward

Main Challenges• Schema evolution

Dramatic impact data and queries Extensive application maintenance Cause unacceptable system downtime

• Becoming a bigger problem More collaboration (web-databases) No downtime (300K$/hours) Larger databases

• Method/tool must support Predict and evaluate the effect of schema changes Rewrite queries and applications Migrate the data


Problem Context: The Power of RDBMSs


Physical

Logical

View 1 View 2 View n

DBMSs

Prism

WikeMedia Schema Change


oidtitleuser

minortext

timestamp

oidtitleuser

minortext

timestampis_new

is_redirect

V41

pidtitle

is_newis_redirect

latest

ridpageiduser

minortimestamp

tidtext

V42

old

cur

page

revision

text


Schema Change: Effect Queries• Get current information about Auckland entry

SELECT cur.textFROM curWHERE cur.title = ’Auckland’

SELECT text.textFROM page, revision, textWHERE page.pid = revision.pageAND revision.rid = text.tidAND page.latest = revision.ridAND page.title = ’Auckland’

V41

V42

SMO: Diagram and Specification


SMO: Examples


partition merge

decompose join

SMO Overview (Schema and Data)


SMO Characteristics


Prism: The Architecture


Prism: The Workflow


[source: http://yellowstone.cs.ucla.edu:8180/Prism2/Prism.html#]

Prism: A Screen Dump

Database Specialization Course 2010 15[source: http://yellowstone.cs.ucla.edu:8180/Prism2/Prism.html#]

Prism: Performance


Conclusion• Tool that support schema evolution and data/query

migration Provides a method (and naturally a tool) for the DBA Available online for testing

• Tool used on real-world non-trivial examples• Data provenance

Documentation of what is done

• Schema modification almost entirely be automated 97% in tested, i.e., 3% manually

• Data/query migration performance well



Good• Relevant problem

Bridges the theoretical world with practice Provides an operational tool

• Real-world, non-trivial running example• Makes practical use of existing research• Validation:

“practical soundness and completeness” “theoretical advances into practical solutions”

• Round-trip, e.g., forward and backward Data provenance

Could be improve• What happens if you drop a table is the data then gone?

Can you then go back (flash-back) “system stores and maintains the schema layout history….”

• “chase-based query rewriting” p764 unclear• Better description of key mappings in running example

Handling of constraints in general

• Too many foot notes• Minor errors

Some spelling errors “gygabytes” DED introduced multiple times

• Table 1 misplaced• Dislikes SELECT * (p763) but uses it later (p. 769)• Is (unique, perfect) values (no, yes) impossible in Table 3?


graceful database schema evolution: the prism workbench

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