Multi-user Database Multi-user Database ProcessingProcessing

ArchitecturesArchitecturesTransactionsTransactionsSecuritySecurityAdministrationAdministration

Multi-user Processing Architectures

Teleprocessing Systems Teleprocessing Systems Client-Server SystemsClient-Server Systems File Sharing SystemsFile Sharing Systems Distributed Database SystemsDistributed Database Systems

Teleprocessing Systems Central CPU & ApplicationsCentral CPU & Applications Central DBMSCentral DBMS Central DatabaseCentral Database

Communication lines

Client-Server Systems Distributed CPUs & ApplicationsDistributed CPUs & Applications Central Central

DBMSDBMS Central Central

DBDB

File Sharing Systems Distributed CPUs & Applications Distributed CPUs & Applications Distributed Distributed

DBMSDBMS Central Central

DB DB

Distributed Database Systems

Distributed Distributed CPUs & CPUs & ApplicationsApplications

Distributed Distributed DBMSDBMS

Distributed Distributed DBDB

Alternative CPU Application DBMS Database

Teleprocessing C C C C

Client Server D D C C

File Sharing D D D C

Distributed D D D D

Alternative CPU Application DBMS Database

Teleprocessing C C C C

Client Server D D C C

File Sharing D D D C

Distributed D D D DC = centralized, D = distributed

Comparing Architectures

No Yes

No NonpartitionedNonreplicated

PartitionedNonreplicated

YesNonpartitioned

ReplicatedPartitionedReplicated

No Yes

No NonpartitionedNonreplicated

PartitionedNonreplicated

YesNonpartitioned

ReplicatedPartitionedReplicatedR

eplic

atio

nTypes of Distributed

Databases

Partition

UnifedDatabase

DistributedDatabase

SingleNonpartionedNonreplicated

PartitionedNonreplicated

NonpartitionedReplicated

PartitionedReplicated

Distributed Database Continuum

Simplicity Security Affordability

Independence Flexibility

Availability

Distributed DBs: Your turn An example of distributed database!An example of distributed database!

Partitioned?Partitioned? Replicated?Replicated? 3 ad3 advantages?vantages?

IndependenceIndependence FlexibilityFlexibility AvailabilityAvailability

3 disadvantages?3 disadvantages? ComplexityComplexity InsecurityInsecurity CostCost

Database Reliability Concurrency controlConcurrency control

Hide other usersHide other users Database recoveryDatabase recovery

Hide failuresHide failures

Change CUSTOMER dataChange SALESPERSON dataInsert ORDER data

Alice reads ACCOUNTAlice adds $50Bob reads ACCOUNTAlice writes ACCOUNTBob takes $100Bob writes ACCOUNT

Database Transactions TransactionTransaction = logical unit of work = logical unit of work Series of actions defined such that Series of actions defined such that

either all of them or none of them are either all of them or none of them are performedperformed

Should always Should always transform the transform the database from database from one consistent one consistent state to anotherstate to another

Start TransactionChange CUSTOMER dataChange SALESPERSON dataInsert ORDER data

If no errors thenCommit Transaction

ElseRollback Transaction

End If

BEGIN TRANSACTION

COMMIT ROLLBACK

Transaction Outcomes

If successful, transaction is committed If successful, transaction is committed & database reaches a new state& database reaches a new state

If unsuccessful, transaction is aborted & If unsuccessful, transaction is aborted & database must be restored to previous database must be restored to previous statestate

Problems Caused by Concurrency

Lost updateLost update Overwrite another user’s updateOverwrite another user’s update

Uncommitted dependency Uncommitted dependency When user sees intermediate step of When user sees intermediate step of

another transaction before it is committedanother transaction before it is committed Inconsistent analysis Inconsistent analysis

Read partial results of incomplete update Read partial results of incomplete update transaction transaction

Concurrency Control

Goal: Goal: SerializabilitySerializability concurrent transactions concurrent transactions

produce same result produce same result as serial executionas serial execution

Technique: Technique: LockingLockingAlice reads ACCOUNTAlice adds $50Alice writes ACCOUNTBob reads ACCOUNTBob takes $100Bob writes ACCOUNT

Two-Phase Locking Transaction can obtain locks as neededTransaction can obtain locks as needed Once first lock is released, no other locks Once first lock is released, no other locks

may be obtainedmay be obtained Guarantees Guarantees

serializabilityserializabilityA1. Lock item 100A2. Read item 100A3. Reduce count by 5A4. Write item 100

B1. Lock item 100B2. Read item 100B3. Reduce count by 3B4. Write item 100

1. Lock item 100 for A2. Read item 100 for A3. Lock item 100 for B; cannot, so place B in wait state4. Set item count to 5 for A5. Write item 100 for A6. Release A's lock on item 1007. Place lock on item 100 for B8. Read item 100 for B9. Set item count to 2 for B10. Write item 100 for B11. Release B's lock on item 100

Dealing with Deadlock

Two-phase locking can lead to deadlockTwo-phase locking can lead to deadlock PreventionPrevention

All or nothing lockingAll or nothing locking Detection and RecoveryDetection and Recovery

DBMS detects deadlock and aborts one of DBMS detects deadlock and aborts one of the transactionsthe transactions

1. Lock paper for user A2. Lock pencils for user B3. Process A's requests; write paper record4. Process B's requests; write pencil record5. Put A in wait state for pencils6. Put B in wait state for paper[Deadlock…]

Recovery via Reprocessing

Return to known point and reprocess Return to known point and reprocess the transactionsthe transactions

Requires database save and log of Requires database save and log of transactionstransactions

Problems:Problems: InefficiencyInefficiency Asynchrony may lead to different end Asynchrony may lead to different end

resultsresults

Recovery via Roll-back Requires log of changes made to databaseRequires log of changes made to database Undo changes made by erroneous or Undo changes made by erroneous or

incomplete transactions, restart valid incomplete transactions, restart valid transactionstransactions

Recovery via Roll-forward Requires database save and log of Requires database save and log of

changes made to databasechanges made to database Restore database save and apply changes Restore database save and apply changes

from logfrom log Frequent checkpoints decrease delayFrequent checkpoints decrease delay

Security

Set by DBA, enforced by DBMSSet by DBA, enforced by DBMS Authorization RulesAuthorization Rules = table in which each = table in which each

record keeps processing permissions via record keeps processing permissions via the following fields:the following fields: Subject - user, group, application, computer...Subject - user, group, application, computer... Object - database, relation, row, column, view, Object - database, relation, row, column, view,

transaction…(transaction…(GranularityGranularity = size of objects) = size of objects) Action - read, write, execute, create, grant...Action - read, write, execute, create, grant... Authorization constraint - limit...Authorization constraint - limit...

Actual DBMS security

The capabilities of the Authorization Rules The capabilities of the Authorization Rules model are only partially implementedmodel are only partially implemented Subject-oriented securitySubject-oriented security

For each subject, binary Action/Object tableFor each subject, binary Action/Object table

Object-oriented securityObject-oriented security For each object, binary Action/Subject tableFor each object, binary Action/Subject table

Constraints via programmable exitsConstraints via programmable exits Triggers to constraint-checking programsTriggers to constraint-checking programs

DBA Responsibilities Manage the DB structureManage the DB structure

Contribute to DB & application developmentContribute to DB & application development Maintain Maintain documentationdocumentation to facilitate changes to facilitate changes

Manage data activityManage data activity Data standards & documentationData standards & documentation Establish and maintain the DB Establish and maintain the DB data dictionarydata dictionary SecuritySecurity Backup & recoveryBackup & recovery

Manage the DBMS softwareManage the DBMS software