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Oracle Architecture

Oracle Architecture. Overview. Oracle terms. Schema – logical collection of user’s objects Tablespace – logical space used for storage Datafile – physical file used for storage Extent – group of contiguous blocks Block – unit of physical storage. Oracle Architecture. database vs. instance.

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Oracle Architecture

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  1. Oracle Architecture Overview

  2. Oracle terms • Schema – logical collection of user’s objects • Tablespace – logical space used for storage • Datafile – physical file used for storage • Extent – group of contiguous blocks • Block – unit of physical storage

  3. Oracle Architecture • database vs. instance Database Instance Parameter files* Control files** Data files Redo Log files System Global Area (SGA) Background Processes Memory Disk * Parameter files include the init<SID>.ora and config<SID>.ora files. These are used to set options for the database. ** Control files contain information about the db in binary form. They can be backed up to a text file however.

  4. Oracle vs. Access and MySQL • Access • One .mdb file contains all objects • Limited roles/permissions • MySQL • Three files per table • Permissions based on user, database, and host • Oracle • Many files • Many roles/permissions possible

  5. The Oracle Data Dictionary • Collection of tables and views that show the inner workings and structure of the db • “static” data dictionary views • owned by SYS • created by catalog.sql script at db creation • contain DDL info • dynamic data dictionary views • also referred to as V$ views • based on virtual tables (X$ tables) • provide info about the instance

  6. More Data Dictionary Create table samples ( ID number(3) primary key, Type varchar2(5), Constraint type_ck check (type in (‘photo’,’swatch’)) …); 1. Samples table created in user’s schema 2. Primary key index created in user’s schema (SYS_C984620) 3. Data dictionary is also updated, with rows being inserted into tables underlying the following data dictionary views: User_objects User_constraints User_cons_columns And lots more…

  7. Oracle Odds and Ends • Dual table • % - the SQL wildcard • inserting apostrophes • Case sensitive string matching SELECT 1+1*400 FROM DUAL; SELECT ename FROM emp WHERE ename like ‘%neil%’; INSERT INTO emp (name) VALUES (‘O’’Neill); UPDATE emp SET ename=UPPER(ename) WHERE ename='O''Neill';

  8. Sysdate • Sysdate returns current system date AND time • use trunc function to remove time piece Example: select to_char (adate, ‘dd-mon-yy hh24:mi:ss’) TO_CHAR(ADATE, ‘DD-MON-YY:HH24:MI:SS’) 17-feb-00 23:41:50 select adate from samples where trunc(adate)=‘17-feb-00’; ADATE 17-FEB-00

  9. ROWID • ROWID is an internal number Oracle uses to uniquely identify each row • NOT a primary key! Is the actual location of a row on a disk. Very efficient for retrieval. • Format specifies block, row, and file (and object in 8) • Oracle 7: BBBBBBB.RRRR.FFFFF • Oracle 8: OOOOOO.FFF.BBBBBB.RRR • Called pseudo-column since can be selected

  10. Outer joins in Oracle • Add (+) to table where nulls are acceptable SELECT * FROM emp, dept WHERE emp.deptno(+)=dept.id;

  11. Oracle SQL functions • Upper(), lower() • Substr(), replace(), rtrim(), concat() • Length() • Floor(), sqrt(), min(), max(), stddev() • Add_months(), months_between(), last_day() • To_date(), to_char(), to_lob()

  12. More functions • nvl() • If NULL, return this instead… Nvl(lastname,’Anonymous’) • decode() • Sort of like an If/Then statement… Decode(gender,0,’Male’,1,’Female’,’Unknown’)

  13. Oracle error messages • Divided into groups by first three letters (e.g. ORA or TNS) • Number gives more information about error • Several messages may be related to only one problem • oerr facility

  14. Constraints • Primary key • Foreign key • Unique, not null • Check • Name your constraints • User_constraints, user_cons_columns CREATE TABLE test ( id NUMBER(2), col2 VARCHAR2(2), col3 VARCHAR2(3), CONSTRAINT test_pk PRIMARY KEY(id), CONSTRAINT col3_ck CHECK (col3 IN ('yes','no')) );

  15. SELECT user_constraints.constraint_name name, constraint_type type, user_constraints.search_condition FROM user_constraints, user_cons_columns WHERE user_constraints.table_name=user_cons_columns.table_name AND user_constraints.constraint_name=user_cons_columns.constraint_name AND user_constraints.owner=user_cons_columns.owner AND user_constraints.table_name=‘TEST’; NAME T SEARCH_CONDITION --------------- - ------------------------- COL3_CK C col3 IN ('yes','no') TEST_PK P

  16. Constraints • Oracle naming of constraints is NOT intuitive! • enabling and disabling disable constraint constraint_name; • the EXCEPTIONS table • run utlexcpt.sql to create EXCEPTIONS table then • alter SQL statement: SQL_query EXCEPTIONS into EXCEPTIONS;

  17. More objects • Sequences • creating the sequence create sequence CustomerID increment by 1 start with 1000; • selecting from the sequence insert into customer (name, contact, ID) values (‘TManage’,’Kristin Chaffin’,CustomerID.NextVal); • CurrVal is used after NextVal for related inserts • Synonyms • provide location and owner transparency • Can be public or private

  18. PL/SQL - Triggers • Executed on insert, update, delete • Use to enforce business logic that can’t be coded through referential integrity or constraints • Types of triggers • row level (use FOR EACH ROW clause) • statement level (default) • Before and After triggers • Referencing old and new values

  19. Trigger example SQL> desc all_triggers; Name Null? Type ------------------------------- -------- ---- OWNER VARCHAR2(30) TRIGGER_NAME VARCHAR2(30) TRIGGER_TYPE VARCHAR2(16) TRIGGERING_EVENT VARCHAR2(75) TABLE_OWNER VARCHAR2(30) BASE_OBJECT_TYPE VARCHAR2(16) TABLE_NAME VARCHAR2(30) COLUMN_NAME VARCHAR2(4000) REFERENCING_NAMES VARCHAR2(128) WHEN_CLAUSE VARCHAR2(4000) STATUS VARCHAR2(8) DESCRIPTION VARCHAR2(4000) ACTION_TYPE VARCHAR2(11) TRIGGER_BODY LONG

  20. Trigger example (cont.) SQL> select trigger_name from all_triggers where owner='SCOTT'; TRIGGER_NAME ------------------------------ AFTER_INS_UPD_ON_EMP set lines 120 col trigger_name format a20 col triggering_event format a18 col table_name format a10 col description format a26 col trigger_body format a35 select trigger_name, trigger_type, triggering_event, table_name, status, description, trigger_body from all_triggers where trigger_name='AFTER_INS_UPD_ON_EMP';

  21. Trigger example (cont.) SQL> / TRIGGER_NAME TRIGGER_TYPE TRIGGERING_EVENT TABLE_NAME STATUS DESCRIPTION -------------------- ---------------- ------------------ ---------- -------- ----------------------- TRIGGER_BODY ----------------------------------- AFTER_INS_UPD_ON_EMP BEFORE EACH ROW INSERT OR UPDATE EMP ENABLED scott.after_ins_upd_on_emp before insert or update on scott.emp for each row begin :new.ename := upper(:new.ename); end; The above trigger was created with the following statement: create or replace trigger scott.after_ins_upd_on_emp before insert or update on scott.emp for each row begin :new.ename := upper(:new.ename); end;

  22. Remember those views? • Query USER_TRIGGERS to get trigger info • Query USER_SOURCE to get source of procedure, function, package, or package body • Query USER_ERRORS to get error information (or use show errors) col name format a15 col text format a40 select name, type, text from user_errors order by name, type, sequence; • Query USER_OBJECT to get status info

  23. Understanding Indexes • Index overhead • impact on inserts, updates and deletes • batch inserts can be slowed by indexes - may want to drop, then recreate • rebuilding indexes • Use indexes when query will return less than 5% of rows in a large table • Determining what to index • All primary and foreign keys • Examine SQL and index heavily hit, selective columns (columns often found in where clauses)

  24. What not to Index…preferably • columns that are constantly updated • columns that contain a lot of null values • columns that have a poor distribution of data • Examples: • yes/no • true/false • male/female

  25. B*-tree index Miller Branch blocks < Miller > Miller < Davis Davis Jones Smith Turner Turner > Adams Brown Culver Deal Howard Isis Jules Klein Main Moss Porter Sikes Sykes Thomas Topper Vera Wagner Yanks Leaf blocks Deal – ROWID Howard – ROWID Isis - ROWID Detail of leaf node Figure 4-1. in Oracle Essentials (2001). Greenwald, et.al. O’Reilly. p 92

  26. Bitmap index Parts table partno color size MEDMEDSMALLLARGE 1 2 3 4 GREEN RED REDBLUE Bitmapped index on ‘color’ color = ‘BLUE’ color = ‘RED’ color = ‘GREEN’ 0 0 0 1 0 1 1 0 1 0 0 0 Part number 1 2 3 4 Figure 4-2. in Oracle Essentials (2001). Greenwald, et.al. O’Reilly. p 95

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