Materialized Views

MATERIALIZED VIEWS

- WISSENSWERTES UND NEUERUNGEN IN 12C

AUTHOR: JONAS GASSENMEYER

www.syntegris.de

@gassenmj

Stand 42

© SYNTEGRIS INFORMATION SOLUTIONS GMBH AGENDA . Vorstellung (2 Minuten) . Use Case Pharma Konzern (3 Minuten) •Wissenswertes (vor 12c) .Was ist eine MV, (SQL Hinterlegen und Index drauf) (2 Minuten) .Query Rewrite (1 Minuten) .Atomic_refresh (5 Minuten) .Tablespace (1 Minute) .Fast refresh (incrementell) (5 Minuten) .„es kommt drauf an“ (1 Minuten)

• Out of place refresh . Prebuilt table (3 Minuten) . Demo (3 Minuten)

• On Statement MVs . Erklärung (3 Minuten) . Demo (3 Minuten)

• Real time MVs . Erklärung (3 Minuten) . Demo (3 Minuten)

Refresh Statistiken

.Erklärung (3 Minuten) .Demo (3 Minuten) .Bug?

Fazit (3 Minuten)

Table Table Table complex Tables MView fast select Report aggregation

runs when user runs at night requests the report

Materialized View pre-computes result sets

› Use Case - Replication

Database Local DB MView Link Table Remote DB

Data

Materialized View copies remote data to local DB

› Ordering Vials/Tubes/Plates

Differ on each Site → Aggregation From ca. 50 Mio aggregated to ca. 6.5 Mio

› Metadata about Substances

Same on each Site → Replication Ca. 18.5 Mio

Registration System

PL/SQL API

Frankfurt (Master)

MV MV MV MV

Boston Tucson Paris Toulouse

Web Interface

Synonyms

Global Ordering

MV MV MV MV

~50 Mio aggregated to ~6.5 Mio

Boston Tucson Paris Toulouse

CREATE MATERIALIZED VIEW abc_mv AS SELECT * from abc@remotedb;

DROP MATERIALIZED VIEW abc_mv;

CREATE MATERIALIZED VIEW schema.mv_name TABLESPACE TBS_NOLOG BUILD DEFERRED USING INDEX REFRESH COMPLETE ON DEMAND DISABLE QUERY REWRITE AS (SELECT /*+ driving_site (r1)*/ col1 ,col2 ,… FROM schema.table1@db_link alias_remote_table r1, schema.table2@db_link alias_remote_table r2 WHERE …;

› Driving site Hint places costs on local/remote site

› Consider to use Oracles JOIN Syntax!

CREATE MATERIALIZED VIEW schema.mv_name AS (SELECT /*+ driving_site (alias_remote_table)*/ col1 ,col2 ,… FROM schema.table1@db_link alias_remote_table1, schema.table2@db_link alias_table2 WHERE alias_table2.join = alias_remote_table1.join col3 = ‘xy‘;

http://docs.oracle.com/database/122/SQLRF/Comments.htm#GUID-DDABFD2E-FE80-4A2D-99D2-87E61EFA2182

› Nolog Tablespace

› Backup/Redo might not be needed

› In case of Recovery: complete refresh against master table

CREATE MATERIALIZED VIEW schema.mv_name TABLESPACE TBS_NOLOG AS (SELECT col1 ,col2 ,… FROM schema.table1@db_link WHERE …;

Table Complete refresh MView

Incremental refresh Table MView MV Incremental refresh LOG

Incremental refresh

› AFTER ROW TRIGGER logs changes in master table

› additional Table MLOG$_master_name

› master instance must provide extra space for those logs

› Special:

fast refresh direct path operations on masters

unregister MVs which are not used anymore!

› PRIMARY KEY LOGIC CREATE MATERIALIZED VIEW LOG ON master_table › ROWID PHYSICAL WITH PRIMARY KEY,ROWID INCLUDING NEW VALUES;

CREATE MATERIALIZED VIEW mv_name REFRESH WITH ROWID AS SELECT * FROM table@db_link;

› IMPACT: Reorganization and truncating of the master table is difficult FAST REFRESH will TURN into a COMPLETE REFRESH

CREATE MATERIALIZED VIEW schema.mv_name TABLESPACE TBS_NOLOG ON PREBUILD TABLE USING INDEX REFRESH COMPLETE ON DEMAND DISABLE QUERY REWRITE AS (SELECT /*+ driving_site (r1)*/ col1 ,col2 ,… FROM schema.table1@db_link alias_remote_table r1, schema.table2@db_link alias_remote_table r2 WHERE …;

BEGIN DBMS_SCHEDULER.CREATE_JOB ( job_name => ‘JOB_REFRESH_MAT_VIEWS_MASTER', job_type => 'STORED_PROCEDURE', job_action => 'REFRESH_MAT_VIEWS_MASTER’, repeat_interval => 'FREQ=MINUTELY;INTERVAL=10’, comments => 'fast refresh for MV'); END; / dbms_mview.refresh('MV', 'C’, atomic_refresh => FALSE );

Is not possible in MVs Definition!

› Special Options DELETE › MV is readable all the time

› Index maintenance during delete and INSERT insert SELECT › Default since 10g

› REDO and UNDO COMMIT

MView

TRUNCATE › truncate faster than delete (high water mark)

INSERT › minimal Index maintenance /*+append*/ SELECT › append hint used during insert (direct path load)

COMMIT › MView empty during refresh (MV readable?)

› No UNDO (truncate) and less REDO MView (append)

manual execution or regular job

dbms_mview.refresh

Table MView

Refresh

commit

Table MView

Refresh

CREATE MATERIALIZED VIEW schema.mv_name TABLESPACE TBS_NOLOG BUILD DEFERRED USING INDEX REFRESH FAST ON STATEMENT DISABLE QUERY REWRITE AS (SELECT /*+ driving_site (r1)*/ col1 ,col2 ,… FROM schema.table1@db_link alias_remote_table r1, schema.table2@db_link alias_remote_table r2 WHERE …;

Any DML before commit Table join MView Table Refresh

create MV build deferred MV empty

Table

MV complete refresh with Data

DEFAULT = BUILD IMMEDIATE

create table as select prebuild table create MV Table

Refresh MView

dbms_mview.refresh( 'MV’ , method => ‘?’ , atomic_refresh => false , out_of_place => true );

RV$xxx Refresh table

Table New Segment

MView SQL

CREATE MATERIALIZED VIEW schema.mv_name TABLESPACE TBS_NOLOG ON PREBUILD TABLE USING INDEX REFRESH COMPLETE ON DEMAND ENABLE QUERY REWRITE AS (SELECT /*+ driving_site (r1)*/ col1 ,col2 ,… FROM schema.table1@db_link alias_remote_table r1, schema.table2@db_link alias_remote_table r2 WHERE …;

Select

CBO Tables rewrites the query to use MV Select the MV

CREATE MATERIALIZED VIEW schema.mv_name TABLESPACE TBS_NOLOG BUILD DEFERRED USING INDEX REFRESH FAST ON DEMAND ENABLE QUERY REWRITE ENABLE ON QUERY COMPUTATION AS (SELECT /*+ driving_site (r1)*/ col1 ,col2 ,… FROM schema.table1@db_link alias_remote_table r1, schema.table2@db_link alias_remote_table r2 WHERE …;

Select

CBO Table rewrites the Select query to use MV MV the MV and Incremental LOG reads Delta from refresh MV Logs

› Chris Saxon: https://blogs.oracle.com/sql/12-things- developers-will-love-about-oracle-database-12c-release- 2#real-time-mv

› Uwe Hesse: https://uhesse.com/2017/01/05/real-time- materialized-views-in-oracle-12c/

› SELECT * FROM DBA_MVREF_STATS; SELECT * FROM DBA_MVREF_STATS_SYS_DEFAULTS;

› SELECT * FROM DBA_MVREF_RUN_STATS; SELECT * FROM DBA_MVREF_STATS_PARAMS;

› SELECT * FROM DBA_MVREF_CHANGE_STATS;

› SELECT * FROM DBA_MVREF_STMT_STATS;

Theory Reality

› Improvements (already before von 12c)

› Usability – easy syntax, not much coding required!

› Performance Improvements (espacially 12.2)

› Still some question marks (Bugs?)

› Everybody should use Materialized Views (independent from Your DB Version!). But know when and how.

Feature 12c? Judge

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Statement-Level Refresh 12.2

Refresh Statistics History 12.2

Atomic Refresh x

Out-of-Place Refresh 12.1

Real-Time Materialized Views 12.2

› Data redundancy › reduce network loads

› Additional storage capacity › Mass deployment : templates

› (non-) currentness of data › Site – specific customization (e.g. timing of refresh) › Administrative overhead/ additional Work › Disconnected computing: network connection only during refresh › Strange caching behavior (drop and recreate) › Performance feature

› Multiple options, easy configuration

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