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Distributed Database Management Systems . Lecture 25. Distributed Database Management Systems . Virtual University of Pakistan. In Previous Lectures: time 1:40-230. Reasons for Fragmentation Maximizes local access Reduces table size, etc. PHF using the SQL Server on same machine.

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distributed database management systems1

Distributed Database Management Systems

Virtual University of Pakistan

in previous lectures time 1 40 230
In Previous Lectures: time 1:40-230
  • Reasons for Fragmentation
    • Maximizes local access
    • Reduces table size, etc.
  • PHF using the SQL Server on same machine
in previous lectures 2 00
In Previous Lectures--2:00
  • DDBS design is a team effort
  • Involves
    • Domain Experts
    • DDBS Experts
    • Network Experts
in previous lectures
In Previous Lectures
  • Implemented PHF in a Banking Environment (around 3: 40)
  • DDBS layer is superimposed on the client sites (4:00)
  • Actual Data resides with the local sites (4:35)
today s lecture
Today’s Lecture

Derived Horizontal Fragmentation

derived horizontal fragmentation
Derived Horizontal Fragmentation
  • Fragmenting/ Partitioning a table based on the constraints defined on another table.
  • Both tables are linked with each other through Owner-Member relation
slide8
Owner

a, b, c, d

TABLE1

Link

TABLE2

p, q, r, s, a

Member

Time: 5:36

scenario around 7 25
Scenario (around 7:25)

Owner

titleId, titleName, sal

TITLE

Link

EMP

empId, empName, empAdres, titleId

Member

why dhf here 8 50
Why DHF Here (8: 50)
  • Employee and salary record is split in two tables due to Normalization
  • Storing all data in EMP table introduces Transitive Dependency
  • That causes Anomalies
phf of title table around 11 00
PHF of TITLE table, around 11:00
  • Predicates defined on the sal attribute of TITLE table
  • p1 = sal > 10000 and sal <= 20000
  • p2 = sal > 20000 and sal <= 50000
  • p3 = sal > 50000
conditions for the title table 11 58
Conditions for the TITLE Table (11:58)
  • TITLE1 = (sal > 10000 and SAL ≤30000) (SAL)
  • TITLE2 = (sal > 20000 and SAL ≤50000) (SAL)
  • TITLE3 = (sal > 50000) (SAL)
tables created with constraints 12 20
Tables created with constraints: 12:20
  • create table TITLE1 (titleID char(3) primary key, titleName char (15), sal int check (SAL between 10000 and 20000))
  • create table TITLE2 (titleID char(3) primary key, titleName char (15), sal int check (SAL between 20001 and 50000))
  • create table TITLE3 (titleID char(3) primary key, titleName char (15), sal int check (SAL > 50000))
slide14
TITLE

TITLE3

TITLE1

TITLE2

emp table at local sites 14 45
EMP table at local sites (14:45)
  • create table EMP1 (empId char(5) primary key, empName char(25), empAdres char (30), titleId char(3) foreign key references TITLE1(titleID))
time 15 40
Time 15:40

PHF on

Owner

titleId, titleName, sal

TITLE

Link

empId, empName, empAdres, titleId

EMP

Member

Natural Join with Owner Fragments

referential integrity constraint 18 30
Referential Integrity Constraint (18:30)
  • Null value in the EMP1.titleId is allowed
  • This violates the correctness requirement of the Fragmentation, i.e., it will violating the completeness critetion
tighten up the constraint around 20 00
Tighten Up the Constraint Around 20:00
  • Further we need to impose the “NOT NULL” constraint on the EMP1.titleID
  • Now the records in EMP1 will strictly adhere to the DHF
revised emp1 definition 21 00
Revised EMP1 Definition(21::00)
  • create table EMP1 (empId char(5) primary key, empName char(25), empAdres char (30), titleId char(3) foreign key references TITLE1(titleID) not NULL)
defining all three emp tables 21 20
Defining all three EMP tables:21:20
  • create table EMP1 (empId char(5) primary key, empName char(25), empAdres char (30), titleId char(3) foreign key references TITLE1(titleID) not NULL)
  • create table EMP2 (empId char(5) primary key, empName char(25), empAdres char (30), titleId char(3) foreign key references TITLE2(titleID) not NULL)
  • create table EMP3 (empId char(5) primary key, empName char(25), empAdres char (30), titleId char(3) foreign key references TITLE3(titleID) not NULL)
phf of emp at different sites 22 30
PHF of EMP at different sites (22:30)
  • create table EMP1 (empId char(5) primary key check (empId in ('Programmer')), empName char(25), empAdres char (30), titleId char(3))
slide23
create table EMP2 (empId char(5) primary key check (empId in (‘Elect. Engr’,’Mech. Engr’)), empName char(25), empAdres char (30), titleId char(3))
  • create table EMP3 (empId char(5) primary key check (empId in (' Sys Analyst ')), empName char(25), empAdres char (30), titleId char(3))
slide24
Adding a new record in TITLE

(23:10)

TITLE

TITLE

New Record

time 24 00
Time 24:00
  • All three predicates of PHF defined in the two slide a couple of slides ago
may be 24 40
May be: 24:40
  • create table EMP1 (empId char(5) primary key check (empId in ('Programmer‘, ‘Assist Supr’)), empName char(25), empAdres char (30), titleId char(3))
slide29
EMP1

EMP3

EMP2

slide31
Data replicated as the transaction executes
  • Preferred in higher bandwidth and lower latency
  • Transaction is replicated as it is executed
slide32
Begins with a snapshot, changes sent at subscribers as they occur or at timed intervals
  • A special Type allows changes at subscribers
slide33
Lets do it
  • From the Enterprise Manager, select Replication, after a couple of nexts, we get this screen
slide40
Publication has been created that can be viewed from Replication Monitor or from Replication, like this
slide42
It has also created snapshot and log reader agents, which won’t work until we create a subscription.
  • For this, we select the publication from replication monitor, right click it, then select Push new subscription
slide45
You select the particular database where you want to subscribe, we have created a new one
slide49
After this we run the snapshot agent, that creates a snapshot, you can verify this from snapshot agent history, or you can go to subscriber database and have a look, like this
slide53
This will be automatically be transferred to Subscription.
  • If this activity could not be performed on subscriber, then the replication monitor will generate an error. You have to trap it and tune your application
slide60
Now you execute the snapshot agent of this replication
  • It will create the snapshot, then you subscribe a database
  • We find the original data in the subscriber
  • After this if we make any change on either side, it will be reflected on the other side
slide61
In case of merge replication, we have to be careful about the constraints, like Primary Key, or other constraints
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