Data Distribution & Replication

Transcription

1 Distributed Databases Definitions Data Distribution & Replication A single logical database thatis spread physically across computers in multiple locations thatare connected by a data communications link. Decentralized Database. A collection of independent databases: Homogeneous - Same DBMS at each node. Autonomous - Independent DBMSs. Non-autonomous - Central, coordinating DBMS. Heterogeneous - Different DBMSs at different nodes. Oracle Client Server Sincrona - Asincrona Client / Server - Server / Server $HOME/network/ admin/tnsnames.ora ALIAS = (DESCRIPTION = (ADDRESS = (PROTOCOL= TCP (Host= xxx.yyy.zzz.www (Port= 1526 (CONNECT_DATA = (SID = O920 $HOME/network/ admin/listener.ora Tnsnames.ora Server 1 usr1 / pwd1 T1 TNS - TCP/IP connect system/manager; grant create database link to usr1; grant create synonym to usr1; Listener.ora Server 2 usr2 / pwd2 T2 Alias del tnsnames della macchina server 1 Processo Listener Processo Server x Connessione Dedicata connect usr1/pwd1; create database link dbms2 connect to usr2 identified by pwd2 using alias2 ; create synonym S2 for T2@dbms2; $HOME/network/ admin/sqlnet.ora

2 Two-Phase Commit Case Study Data Distribution Prepare Phase Coordinator receives a commit request Coordinator instructs all resource managers to get ready to go either way on the transaction. Each resource manager writes all updates from that transaction to its own physical log. Coordinator receives replies from all resource managers. If all are ok, it writes commit to its own log; if not then it writes rollback to its log. Commit Phase Coordinator then informs each resource manager of its decision and broadcasts a message to either commit or rollback (abort. If the message is commit, then each resource manager transfers the update from its log to its database. A failure during the commit phase puts a transaction in limbo. Oracle Offers Rows Filter Where SnapShot Read Only Fields Filter Select SnapShot WriteAble Multi Master Site SnapShot UpDateAble CREATE SNAPSHOT snap_unito TABLESPACE tablespace_unito PCTFREE n STORAGE (INITIAL n NEXT n PCTINCREASE 0 MINEXTENTS 1 MAXEXTENTS 121 WITH [ PRIMARY KEY ROWID ] REFRESH [ FAST COMPLETE FORCE ] START WITH date NEXT date AS subquery;

3 Sempre applicabile - Nessun vincolo architetturale REFRESH [ FAST COMPLETE FORCE ] Se possibile adotta tecnica Fast altrimenti Complete Applicabile solo: 1 Se la select è definibile semplice ovvero: a appoggia su un solo oggetto di tipologia tabellare b è priva di costrutti quali group by, order by e subquery 2 Esiste lato Master un Log 3 Il Log esiste da tempo utile per supportare il nuovo refresh CREATE SNAPSHOT snap_unito TABLESPACE tablespace_unito PCTFREE n STORAGE (INITIAL n NEXT n PCTINCREASE 0 MINEXTENTS 1 MAXEXTENTS 121 WITH [ PRIMARY KEY ROWID ] REFRESH [ FAST COMPLETE FORCE ] START WITH date NEXT date FOR UP AS subquery; Note Base: Modifiche in aggiornamento mono direzionale (da Master verso Slave Modifiche perse al successivo refresh Applicazioni in ambiti prevalentemente di simulazione SnapShot View SnapShot View Master Table SnapShot Base Table Master Table SnapShot Base Table Refresh Operation Refresh Operation SnapShot Log View of Changed SnapShot Log View of Changed Log of Change

4 SNP Background Processes Job Schedulati Job Ready Job List Job ReadyList Next? Caso di Failure 1 Tentativo dopo 1 Minuto 2 Tentativo dopo 2 Minuti 3 Tentativo dopo 4 Minuti n Tentativo dopo 2^(n-1 Minuti con 3<n<17 Compatibile con l intervallo di ri-programmazione del Job DBMS_JOB Package To schedule and manage jobs in the job queue, use the procedures in the DBMS_JOB package. There are no database privileges associated with using job queues. Any user who can execute the job queue procedures can use the job queue. Submitting a Job to the Job Queue To submit a new job to the job queue, use the SUBMIT procedure in the DBMS_JOB package: DBMS_JOB.SUBMIT ( job OUT BINARY_INTEGER, what IN VARCHAR2, next_date IN DEFAULT SYS, interval IN VARCHAR2 DEFAULT null, no_parse IN BOOLEAN DEFAULT FALSE declare jobno number; begin DBMS_JOB.SUBMIT (jobno, begin procedura_unito01(1, X ; end;, SYS, SYS + 1 ; commit; end; DBMS_JOB Package Broken Jobs A job is labeled as either broken or not broken. Oracle does not attempt to run broken jobs. However, you can force a broken job to run by calling the procedure DBMS_JOB.RUN. There are two ways a job can break: * Oracle has failed to successfully execute the job after 16 attempts. * You have marked the job as broken, using the procedure DBMS_JOB.BROKEN. DBMS_JOB.BROKEN ( job IN BINARY_INTEGER, broken IN BOOLEAN, next_date IN DEFAULT SYS Once a job has been marked as broken, Oracle will not attempt to execute the job until you either mark the job as not broken, or force the job to be executed by calling the procedure DBMS_JOB.RUN.

5 DBMS_JOB Package In conclusione citiamo le viste del dizionario dati che consentono un monitoring della schedulazione: USER_JOBS DBA_JOBS DBMS_JOB.CHANGE (job IN binary_integer, what IN varchar2, next_date IN date, interval IN varchar2 ; DBMS_JOB.REMOVE (job IN binary_integer, ; JOB LOG_USER PRIV_USER SCHEMA_USER LAST_ LAST_SEC THIS_ THIS_SEC NEXT_ NEXT_SEC TOTAL_TIME BROKEN INTERVAL FAILURES WHAT CURRENT_SESSION_LABEL CLEARANCE_HI CLEARANCE_LO NLS_ENV MISC_ENV NOT NULL NOT NULL VARCHAR2(1 NOT NULL VARCHAR2(200 VARCHAR2(2000 VARCHAR2(2000 RAW(32 DBA_JOBS_RUNNING SID JOB FAILURES LAST_ LAST_SEC THIS_ THIS_SEC Conflict Resolution In modalità Asincrona possono verificarsi conflitti che possono minare la consistenza e l integrità dei dati. Sono prevalentemente di tre tipologie: Update Uniqueness Delete Oracle offre sistemi di Definizione & Risoluzione Automatica dei Conflitti time stamp minimum value maximum value highest priority site highest priority value average. custom solution