Oracle 10g New Features
Oracle 10g New Features
Oracle 10g New Features
Automatic SQL Tuning in Oracle Database 10g
This article the discusses the new features which automate the tuning of SQL statements in Oracle 10g:
Overview
SQL Tuning Advisor
Managing SQL Profiles
SQL Tuning Sets
Useful Views
Overview
In
its normal mode the query optimizer needs to make decisions about
execution plans in a very short time. As a result it may not always be
able to obtain enough information to make the best decision. Oracle 10g
allows the optimizer to run in tuning mode where it can gather
additional information and make recommendations about how specific
statements can be tuned further. This process may take several minutes
for a single statement so it is intended to be used on high-load
resource-intensive statements.
In tuning mode the optimizer performs the following analysis:
Statistics
Analysis - The optimizer recommends the gathering of statistics on
objects with missing or stale statistics. Additional statistics for
these objects are stored in an SQL profile.
SQL
Profiling - The optimizer may be able to improve performance by
gathering additional statistics and altering session specific parameters
such as the OPTIMIZER_MODE. If such improvements are possible the
information is stored in an SQL profile. If accepted this information
can then used by the optimizer when running in normal mode. Unlike a
stored outline which fixes the execution plan, an SQL profile may still
be of benefit when the contents of the table alter drastically. Even so,
it's sensible to update profiles periodically. The SQL profiling is not
performed when the tuining optimizer is run in limited mode.
Access
Path Analysis - The optimizer investigates the effect of new or
modified indexes on the access path. It's index recommendations relate
to a specific statement so where necessary it will also suggest the use
of the SQL Access Advisor to check the impact of these indexes on a
representative SQL workload.
SQL
Structure Analysis - The optimizer suggests alternatives for SQL
statements that contain structures that may impact on performance. The
implementation of these suggestions requires human intervention to check
their validity.
The
automatic SQL tuning features are accessible from Enterprise Manager on
the "Advisor Central" page these or from PL/SQL using the DBMS_SQLTUNE
package. This article will focus on the PL/SQL API as the Enterprise
Manager interface is reasonably intuative.
SQL Tuning Advisor
In order to access the SQL tuning advisor API a user must be granted the ADVISOR privilege:
CONN sys/password AS SYSDBA
GRANT ADVISOR TO scott;
CONN scott/tiger
2) Overview
The
Automatic Database Diagnostic Monitor (ADDM) analyzes data in the
Automatic Workload Repository (AWR) to identify potential performance
bottlenecks. For each of the identified issues it locates the root cause
and provides recommendations for correcting the problem. An ADDM
analysis task is performed and its findings and recommendations stored
in the database every time an AWR snapshot is taken provided the
STATISTICS_LEVEL parameter is set to TYPICAL or ALL. The ADDM analysis
includes:
CPU load
Memory usage
I/O usage
Resource intensive SQL
Resource intensive PL/SQL and Java
RAC issues
Application issues
Database configuration issues
Concurrency issues
Object contention
3) Overview of Automatic Storage Management (ASM)
Automatic
Storage Management (ASM) simplifies administration of Oracle related
files by allowing the administrator to reference disk groups rather than
individual disks and files, which are managed by ASM. The ASM
functionality is an extention of the Oracle Managed Files (OMF)
functionality that also includes striping and mirroring to provide
balanced and secure storage. The new ASM functionality can be used in
combination with existing raw and cooked file systems, along with OMF
and manually managed files.
The
ASM functionality is controlled by an ASM instance. This is not a full
database instance, just the memory structures and as such is very small
and lightweight.
The
main components of ASM are disk groups, each of which comprise of
several physical disks that are controlled as a single unit. The
physical disks are known as ASM disks, while the files that reside on
the disks are know as ASM files. The locations and names for the files
are controlled by ASM, but user-friendly aliases and directory
structures can be defined for ease of reference.
The
level of redundancy and the granularity of the striping can be
controlled using templates. Default templates are provided for each file
type stored by ASM, but additional templates can be defined as needed.
Failure
groups are defined within a disk group to support the required level of
redundancy. For two-way mirroring you would expect a disk group to
contain two failure groups so individual files are written to two
locations.
In summary ASM provides the following functionality:
Manages groups of disks, called disk groups.
Manages disk redundancy within a disk group.
Provides near-optimal I/O balancing without any manual tuning.
Enables management of database objects without specifying mount points and filenames.
Supports large files.
4) Automatic Workload Repository (AWR) in Oracle Database 10g
AWR Features
The AWR is used to collect performance statistics including:
Wait events used to identify performance problems.
Time
model statistics indicating the amount of DB time associated with a
process from the V$SESS_TIME_MODEL and V$SYS_TIME_MODEL views.
Active Session History (ASH) statistics from the V$ACTIVE_SESSION_HISTORY view.
Some system and session statistics from the V$SYSSTAT and V$SESSTAT views.
Object usage statistics.
Resource intensive SQL statements.
The repository is a source of information for several other Oracle 10g features including:
Automatic Database Diagnostic Monitor
SQL Tuning Advisor
Undo Advisor
Segment Advisor
Snapshots
By
default snapshots of the relevant data are taken every hour and
retained for 7 days. The default values for these settings can be
altered using:
BEGIN
DBMS_WORKLOAD_REPOSITORY.modify_snapshot_settings(
retention => 43200, -- Minutes (= 30 Days). Current value retained if NULL.
interval => 30); -- Minutes. Current value retained if NULL.
END;
/
5) DBMS_FILE_TRANSFER Package in Oracle Database 10g
Oracle
10g has introduced the DBMS_FILE_TRANSFER package which provides an API
for copying binary files between database servers.
Common Usage Notes
COPY_FILE
GET_FILE
PUT_FILE
Common Usage Notes
All of the the currently supported procedures have some common usage notes listed below:
The user must have read privilege on the source directory object and write privilege on the destination directory object.
The procedure converts directory object names to uppercase unless they are surrounded by double quotes.
Files to be copied must be multiples of 512 bytes in size.
Files to be copied must be equal to or less than 2 terabytes in size.
File transfers are not transactional.
Files are copied as binary, so no character conversions are performed.
File copies can be monitored using the V$SESSION_LONGOPS view.
COPY_FILE
The COPY_FILE procedure allows you to copy binary files from one location to another on the same server.
GET_FILE
The GET_FILE procedure allows you to copy binary files from a remote server to the local server.
PUT_FILE
The PUT_FILE procedure allows you to copy binary files from the local server to a remote server.
6) Flashback New Features and Enhancements in Oracle Database 10g
Oracle9i
introduced the DBMS_FLASHBACK package to allow queries to reference
older versions of the database. Oracle 10g has taken this technology a
step further making it simpler to use and much more flexible.
Note:
Internally Oracle uses SCNs to track changes so any flashback operation
that uses a timestamp must be translated into the nearest SCN which can
result in a 3 second error.
Flashback Query
Flashback Version Query
Flashback Transaction Query
Flashback Table
Flashback Drop (Recycle Bin)
Flashback Database
Flashback Query Functions
Flashback Query
Flashback
Query allows the contents of a table to be queried with reference to a
specific point in time, using the AS OF clause. Essentially it is the
same as the DBMS_FLASHBACK functionality or Oracle9i, but in a more
convenient form. For example:
CREATE TABLE flashback_query_test (
id NUMBER(10)
);
SELECT current_scn, TO_CHAR(SYSTIMESTAMP, 'YYYY-MM-DD HH24:MI:SS') FROM v$database;
CURRENT_SCN TO_CHAR(SYSTIMESTAM
----------- -------------------
722452 2004-03-29 13:34:12
Flashback Version Query
Flashback
version query allows the versions of a specific row to be tracked
during a specified time period using the VERSIONS BETWEEN clause
Flashback Transaction Query
Flashback
transaction query can be used to get extra information about the
transactions listed by flashback version queries. The VERSIONS_XID
column values from a flashback version query can be used to query the
FLASHBACK_TRANSACTION_QUERY view like:
Flashback Table
The FLASHBACK TABLE command allows point in time recovery of individual tables subject to the following requirements:
You must have either the FLASHBACK ANY TABLE system privilege or have FLASHBACK object privilege on the table.
You must have SELECT, INSERT, DELETE, and ALTER privileges on the table.
There must be enough information in the undo tablespace to complete the operation.
Row movement must be enabled on the table (ALTER TABLE tablename ENABLE ROW MOVEMENT;).
Flashback Drop (Recycle Bin)
In
Oracle 10g the default action of a DROP TABLE command is to move the
table to the recycle bin (or rename it), rather than actually dropping
it. The PURGE option can be used to permanently drop a table.
The
recycle bin is a logical collection of previously dropped objects, with
access tied to the DROP privilege. The contents of the recycle bin can
be shown using the SHOW RECYCLEBIN command and purged using the PURGE
TABLE command. As a result, a previously dropped table can be recovered
from the recycle bin:
Flashback Database
The
FLASHBACK DATABASE command is a fast alternative to performing an
incomplete recovery. In order to flashback the database you must have
SYSDBA privilege and the flash recovery area must have been prepared in
advance.
If the database is in NOARCHIVELOG it must be switched to ARCHIVELOG mode:
CONN sys/password AS SYSDBA
ALTER SYSTEM SET log_archive_dest_1='location=d:\oracle\oradata\DB10G\archive\' SCOPE=SPFILE;
ALTER SYSTEM SET log_archive_format='ARC%S_%R.%T' SCOPE=SPFILE;
ALTER SYSTEM SET log_archive_start=TRUE SCOPE=SPFILE;
SHUTDOWN IMMEDIATE
STARTUP MOUNT
ARCHIVE LOG START
ALTER DATABASE ARCHIVELOG;
ALTER DATABASE OPEN;
Flashback must be enabled before any flashback operations are performed:
CONN sys/password AS SYSDBA
SHUTDOWN IMMEDIATE
STARTUP MOUNT EXCLUSIVE
ALTER DATABASE FLASHBACK ON;
ALTER DATABASE OPEN;
7) Database Security Enhancements in Oracle Database 10g
Virtual Private Database (VPD) Enhancements
Column-Level VPD Policy
Column Masking
Policy Types
Application Context Support for Parallel Queries
Fine-Grained Auditing Enhancements
Uniform Audit Trail
Audit Trail Contents
DBMS_CRYPTO
Virtual Private Database (VPD) Enhancements
Column-Level VPD Policy
In
conventional Virtual Private Database the VPD Policy is applied to the
whole row. By default a Column-Level VPD Policy allows you to restrict
the rows displayed only if specified columns are accessed:
Fine-Grained Auditing Enhancements
Fine-grained auditing now includes support for DML statements in addition to queries:
Uniform Audit Trail
The DBA_COMMON_AUDIT_TRAIL view has been added to display the complete audit trail:
DBA_AUDIT_TRAIL - Standard auditing only (from AUD$).
DBA_FGA_AUDIT_TRAIL - Fine-grained auditing only (from FGA_LOG$).
DBA_COMMON_AUDIT_TRAIL - Both standard and fine-grained auditing.
Audit Trail Contents
Several fields have been added to both the standard and fine-grained audit trails:
EXTENDED_TIMESTAMP - A more precise value than the exising TIMESTAMP column.
PROXY_SESSIONID - Proxy session serial number when an enterprise user is logging in via the proxy method.
GLOBAL_UID - Global Universal Identifier for an enterprise user.
INSTANCE_NUMBER - The INSTANCE_NUMBER value from the actioning instance.
OS_PROCESS - Operating system process id for the oracle process.
TRANSACTIONID
- Transaction identifier for the audited transaction. This column can
be used to join to the XID column on the FLASHBACK_TRANSACTION_QUERY
view.
SCN - System change number of the query. This column can be used in flashback queries.
SQL_BIND - The values of any bind variables if any.
SQL_TEXT - The SQL statement that initiated the audit action.
The SQL_BIND and SQL_TEXT columns are only populated when the AUDIT_TRAIL=DB_EXTENDED initialization parameter is set:
DBMS_CRYPTO
The
DBMS_CRYPTO package is a replacement for the DBMS_OBFUSCATION_TOOLKIT
package available in Oracle 8i and 9i. The new package is easier to use
and contains more cryptographic algorithms:
Cryptographic algorithms - DES, 3DES, AES, RC4, 3DES_2KEY
Padding forms - PKCS5, zeroes
Block cipher chaining modes - CBC, CFB, ECB, OFB
Cryptographic hash algorithms - MD5, SHA-1, MD4
Keyed hash (MAC) algorithms - HMAC_MD5, HMAC_SH1
Cryptographic pseudo-random number generator - RAW, NUMBER, BINARY_INTEGER
Database types - RAW, CLOB, BLOB
8) MERGE Statement Enhancements in Oracle Database 10g
Oracle 10g includes a number of amendments to the MERGE statement making it more flexible.
Test Table
Optional Clauses
Conditional Operations
DELETE Clause
Test Table
The following examples use the table defined below.
CREATE TABLE test1 AS
SELECT *
FROM all_objects
WHERE 1=2;
Optional Clauses
The MATCHED and NOT MATCHED clauses are now optional making all of the following examples valid.
-- Both clauses present.
MERGE INTO test1 a
USING all_objects b
ON (a.object_id = b.object_id)
WHEN MATCHED THEN
UPDATE SET a.status = b.status
WHEN NOT MATCHED THEN
INSERT (object_id, status)
VALUES (b.object_id, b.status);
9) Oracle Data Pump in Oracle Database 10g
Oracle
Data Pump is a newer, faster and more flexible alternative to the "exp"
and "imp" utilities used in previous Oracle versions. In addition to
basic import and export functionality data pump provides a PL/SQL API
and support for external tables.
Getting Started
Table Exports/Imports
Schema Exports/Imports
Database Exports/Imports
Miscellaneous Information
Data Pump API
External Tables
Help
Getting Started
For the examples to work we must first unlock the SCOTT account and create a directory object it can access:
CONN sys/password@db10g AS SYSDBA
ALTER USER scott IDENTIFIED BY tiger ACCOUNT UNLOCK;
GRANT CREATE ANY DIRECTORY TO scott;
CREATE OR REPLACE DIRECTORY test_dir AS '/u01/app/oracle/oradata/';
GRANT READ, WRITE ON DIRECTORY test_dir TO scott;
Table Exports/Imports
The
TABLES parameter is used to specify the tables that are to be exported.
The following is an example of the table export and import syntax:
expdp scott/tiger@db10g tables=EMP,DEPT directory=TEST_DIR dumpfile=EMP_DEPT.dmp logfile=expdpEMP_DEPT.log
impdp scott/tiger@db10g tables=EMP,DEPT directory=TEST_DIR dumpfile=EMP_DEPT.dmp logfile=impdpEMP_DEPT.log
For example output files see expdpEMP_DEPT.log and impdpEMP_DEPT.log.
The TABLE_EXISTS_ACTION=APPEND parameter allows data to be imported into existing tables.
Schema Exports/Imports
The
OWNER parameter of exp has been replaced by the SCHEMAS parameter which
is used to specify the schemas to be exported. The following is an
example of the schema export and import syntax:
expdp scott/tiger@db10g schemas=SCOTT directory=TEST_DIR dumpfile=SCOTT.dmp logfile=expdpSCOTT.log
impdp scott/tiger@db10g schemas=SCOTT directory=TEST_DIR dumpfile=SCOTT.dmp logfile=impdpSCOTT.log
10) Upgrading to Oracle Database 10g
This article provides a brief overview of the areas involved in upgrading existing databases to Oracle 10g including:
Supported Upgrade Paths
Pre-Upgrade Validation Checks
Database Upgrade Assistant (DBCA)
STARTUP UPGRADE
The
whole migration process is beyond the scope of this article so please
refer to the Upgrading a Database to the New Oracle Database 10g Release
document for further information.
Supported Upgrade Paths
Direct
upgrades to 10g are possible from existing databases with versions
listed in the table below. Upgrades from other versions are supported
only via intermediate upgrades to a supported upgrade version.
Original Version
Upgrade Script
8.0.6
u0800060.sql
8.1.7
u0801070.sql
9.0.1
u0900010.sql
9.2.0
u0902000.sql
The
preferred upgrade method is to use the Database Upgrade Assistant
(DBUA), a GUI tool that performs all necessary prerequisite checks and
operations before upgrading the specified instances. The DBUA can be
started directly from the Oracle Universal Installer (OUI) or separately
after the software installation is complete.
Alternatively you may which to perform a manual upgrade which involves the following steps:
Analyze the existing instance using the utlu101i.sql script, explained below.
Backup the database.
Start
the original database in the new upgrade mode (see below) and proceed
with the upgrade. The majority of the upgrade work is done by running
the appropriate upgrade script for the current database version.
Recompile invalid objects.
Troubleshoot any issues or abort the upgrade.
Pre-Upgrade Validation Checks
Oracle
10g includes a script ($ORACLE_HOME/rdbms/admin/utlu101i.sql) which
performs pre-update validation checks on an existing instance. The
script checks a number of areas to make sure the instance is suitable
for upgrade including:
Database version.
Log file sizes.
Tablespace sizes.
Server options.
Initialization parameters (updated, depercated and obsolete).
Database components.
SYSAUX tablespace present.
Cluster information.
Database Upgrade Assistant (DBCA)
The
Database Upgrade Assistant (DBUA) is a GUI tool that guides the user
through the whole upgrade process, including all the steps listed in the
manual upgrade process. The assistant is started using the dbua command
in UNIX and Linux environments or from the Start menu (Start >
Programs > Oracle - HOME_NAME > Configuration and Migration Tools
> Database Upgrade Assistant) in Windows environments.
Once the assistant has started it leads the user through the several steps including:
Selecting the instance to upgrade.
Analyzing the existing database to make sure it is suitable for upgrade.
Creating the SYSAUX tablespace which is required for 10g.
Deciding whether to recompile all invalid objects when the upgrade is complete.
Selecting a backup option for the database.
Deciding how the database should be managed (OEM Console or Grid Control) and defining the appropriate authentication.
Defining the flash recovery area.
Performing any necessary network configuration.
Performing the upgrade process.
Checking the upgrade results.
Listing the changes in default behaviour between the old and new versionsof the database.
Completing the upgrade procedure.
The DBUA can also be started in silent mode provided all the necessary parameters are provided.
STARTUP UPGRADE
The is a new startup mode associated with the upgrade procedure in Oracle 10g.
SQL> STARTUP UPGRADE;
12) Scheduler in Oracle Database 10g
Oracle
10g includes a comprehensive scheduler (DBMS_SCHEDULER) to replace and
extend the functionality provided by the DBMS_JOB package. Jobs form the
core of the functionality, but there are several other components
available:
Programs
Schedules
Jobs
Job Classes
Windows
Windows Groups
Enable, Disable and Attributes
Programs
The
scheduler allows you to optionally create programs which hold metadata
about a task, but no schedule information. A program may related to a
PL/SQL block, a stored procedure or an OS executable file. Programs are
created using the CREATE_PROGRAM procedure:
-- Create the test programs.
BEGIN
-- PL/SQL Block.
DBMS_SCHEDULER.create_program (
program_name => 'test_plsql_block_prog',
program_type => 'PLSQL_BLOCK',
program_action => 'BEGIN DBMS_STATS.gather_schema_stats(''SCOTT''); END;',
enabled => TRUE,
comments => 'Program to gather SCOTT''s statistics using a PL/SQL block.');
Services in Oracle Database 10g
In
Real Application Cluster (RAC) environments it is sometimes desirable
to run applications on a subset of RAC nodes, or have preferred nodes
for specific applications. In Oracle 10g this is accomplished using
services.
Cluster Configuration
Service Creation
Jobs and Services
Connections and Services
Cluster Configuration
For
services to function correctly the GSD daemon must be running on each
node in the cluster. The GSD daemons are started using the gsdctl
utility, which is part of the Cluster Ready Services (CRS) installation,
so they must be started from that environment as follows.
# Set environment.
export ORACLE_HOME=/u01/app/oracle/product/10.1.0/crs
export PATH=$ORACLE_HOME/bin:$PATH
# Start GSD daemon.
gsdctl start
SQL*Plus Enhancements in Oracle Database 10g
Whitespace Support in Windows Path and File Names
Glogin, Login and Predefined Variables
APPEND, CREATE and REPLACE extensions to SPOOL and SAVE
SHOW RECYCLEBIN
Miscellaneous Enhancements
Whitespace Support in Windows Path and File Names
Support
for whitespaces in file names has been added to the START, @, @@, RUN,
SPOOL, SAVE and EDIT commands. Names containing whitespaces must be
quoted for them to be recognised correctly:
SPOOL "My Report.txt"
@"My Report.sql"
Glogin, Login and Predefined Variables
The
user profile files, glogin.sql and login.sql are now run after each
successful connection in addition to SQL*Plus startup. This is
particularly useful when the login.sql file is used to set the SQLPROMPT
to the current connection details.
Three new predefined variables have been added to SQL*Plus:
_DATE - Contains the current date or a user defined fixed string.
_PRIVILEGE - Contains privilege level such as AS SYSDBA, AS SYSOPER or blank.
_USER - Contains the current username (like SHOW USER).
An example of their use would be:
SET SQLPROMPT "_USER'@'_CONNECT_IDENTIFIER _PRIVILEGE _DATE> "
The values of the variables can be viewed using the DEFINE command with no parameters.
APPEND, CREATE and REPLACE extensions to SPOOL and SAVE
The following extentions have been added to the SPOOL and SAVE commands:
REPLACE - (Default) This option replaces an existing file or creates it if it is not already present.
CREATE - This option creates a new file or produces an error if the file already exists.
APPEND - This option appends to an existing file, or creates a new file if it's not already present.
Performance Tuning Enhancements in Oracle Database 10g
Oracle 10g includes many performance tuning enhancements including:
Automatic Performance Diagnostic and Tuning Features
Automatic Shared Memory Management
Wait Model Improvements
Automatic Optimizer Statistics Collection
Dynamic Sampling
CPU Costing
Optimizer Hints
Rule Based Optimizer Obsolescence
Tracing Enhancements
SAMPLE Clause Enhancements
Hash Partitioned Global Indexes
Automatic Performance Diagnostic and Tuning Features
Oracle 10g includes several features related to automatic performance diagnostics and tuning including:
Automatic Optimizer Statistics Collection - The name says it all.
Automatic
Workload Repository (AWR) - An extended version of the STATSPACK
repository that is the heart of all the new diagnostics and tuning
features.
Automatic
Database Diagnostic Monitoring (ADDM) - An automatic diagnostics and
tuning tool which uses the information stored in the AWR.
Automatic SQL Tuning Advisor - A built in SQL tuning feature.
Most of these features are beyond the scope of this article and as such will be dealt with in separate aticles.
Automatic Shared Memory Management
Automatic
Shared Memory Management puts Oracle in control of allocating memory
within the SGA. The SGA_TARGET parameter sets the amount of memory
available to the SGA. This parameter can be altered dynamically up to a
maximum of the SGA_MAX_SIZE parameter value. Provided the
STATISTICS_LEVEL is set to TYPICAL or ALL and the SGA_TARGET is set to a
value other than "0" Oracle will control the memory pools which would
otherwise be controlled by the following parameters:
DB_CACHE_SIZE (default block size)
SHARED_POOL_SIZE
LARGE_POOL_SIZE
JAVA_POOL_SIZE
If
these parameters are set to a non-zero value they represent the minimum
size for the pool. These minimum values may be necessary if you
experience application errors when certain pool sizes drop below a
specific threshold.
The following parameters must be set manually and take memory from the quota allocated by the SGA_TARGET parameter:
DB_KEEP_CACHE_SIZE
DB_RECYCLE_CACHE_SIZE
DB_nK_CACHE_SIZE (non-default block size)
STREAMS_POOL_SIZE
LOG_BUFFER
Wait Model Improvements
A number of views have been updated and added to improve the wait model. The updated views include:
V$EVENT_NAME
V$SESSION
V$SESSION_WAIT
The new views include:
V$ACTIVE_SESSION_HISTORY
V$SYSTEM_WAIT_HISTORY
V$SESS_TIME_MODEL
V$SYS_TIME_MODEL
V$SYSTEM_WAIT_CLASS
V$SESSION_WAIT_CLASS
V$EVENT_HISTOGRAM
V$FILE_HISTOGRAM
V$TEMP_HISTOGRAM
The following are some examples of how these updates can be used.
The
V$EVENT_NAME view has had three new columns added (WAIT_CLASS_ID,
WAIT_CLASS# and WAIT_CLASS) which indicate the class of the event. This
allows easier aggregation of event details:
User I/O .109552
9 rows selected.
The
V$SESSION view has had several columns added that include blocking
session and wait information. The wait information means it's no longer
necessary to join to V$SESSION_WAIT to get wait information for a
session:
-- Display blocked session and their blocking session details.
SELECT sid, serial#, blocking_session_status, blocking_session
FROM v$session
WHERE blocking_session IS NOT NULL;
no rows selected
-- Display the resource or event the session is waiting for.
SELECT sid, serial#, event, (seconds_in_wait/1000000) seconds_in_wait
FROM v$session
ORDER BY sid;
The
V$SYSTEM_WAIT_HISTORY view shows historical wait information which
allows you to identify issues after the session has ended.
Automatic Optimizer Statistics Collection
By
default Oracle 10g automatically gathers optimizer statistics using a
scheduled job called GATHER_STATS_JOB. By default this job runs within a
maintenance windows between 10 P.M. to 6 A.M. week nights and all day
on weekends. The job calls the DBMS_STATS.GATHER_DATABASE_STATS_JOB_PROC
internal procedure which gathers statistics for tables with either
empty or stale statistics, similar to the
DBMS_STATS.GATHER_DATABASE_STATS procedure using the GATHER AUTO option.
The main difference is that the internal job prioritizes the work such
that tables most urgently requiring statistics updates are processed
first.
In
some cases automatically gathering statistics can cause problems.
Highly volatile tables and load tables may have their statistics
gathered when there is an unrepresentative number of rows present. These
situations can be avoided by using one of two methods:
The
current statistics can be deleted and locked to prevent DBMS_STATS from
gathering new statistics. If the OPTIMIZER_DYNAMIC_SAMPLING parameter
is set to 2 (the default) or higher the necessary statistics will be
gathered as part of the query optimization stage (See Dynamic Sampling):
· BEGIN
· DBMS_STATS.delete_table_stats('MY_SCHEMA','LOAD_TABLE');
· DBMS_STATS.lock_table_stats('MY_SCHEMA','LOAD_TABLE');
· END;
/
The statistics can be gathered then locked at a time when the table contains the appropriate data:
· BEGIN
· DBMS_STATS.gather_table_stats('MY_SCHEMA','LOAD_TABLE');
· DBMS_STATS.lock_table_stats('MY_SCHEMA','LOAD_TABLE');
· END;
/
System statistics and statistics for fixed object, such as dynamic performance tables, are not gathered automatically.
Dynamic Sampling
Dynamic sampling enables the server to improve performance by:
Estimate single-table predicate selectivities where available statistics are missing or may lead to bad estimations.
Estimate statatistics for tables and indexes with missing statistics.
Estimate statatistics for tables and indexes with out of date statistics.
Dynamic
sampling is controled by the OPTIMIZER_DYNAMIC_SAMPLING parameter which
accepts values from "0" (off) to "10" (agressive sampling) with a
default value of "2". At compile-time Oracle determines if dynamic
sampling would improve query performance. If so it issues recursive
statements to estimate the necessary statistics. Dynamic sampling can be
beneficial when:
The sample time is small compared to the overall query execution time.
Dynamic sampling results in a better performing query.
The query may be executed multiple times.
In
addition to the OPTIMIZER_DYNAMIC_SAMPLING system parameter the dynamic
sampling level can be set using the DYNAMIC_SAMPLING optimizer hint for
specific queries like:
SELECT /*+ dynamic_sampling(emp 10) */
empno, ename, job, sal
FROM emp
WHERE deptno = 30;
The
results of dynamic sampling are repeatable provided no rows are
inserted, updated or deleted from the sampled table. The
OPTIMIZER_FEATURES_ENABLE parameter will turns off dynamic sampling if
it is set to a version earlier than 9.2.0.
CPU Costing
By default the cost model for the optimizer is now CPU+I/O, with the cost unit as time.
Optimizer Hints
New hints:
SPREAD_MIN_ANALYSIS - Specifies analysis options for spreadsheets.
USE_NL_WITH_INDEX - Specifies a nested loops join.
QB_NAME - Specifies a name for a query block.
NO_QUERY_TRANSFORMATION - Prevents the optimizer performing query transformations.
NO_USE_NL,
NO_USE_MERGE, NO_USE_HASH, NO_INDEX_FFS, NO_INDEX_SS and
NO_STAR_TRANSFORMATION - Excludes specific operations from the query
plan.
INDEX_SS, INDEX_SS_ASC, INDEX_SS_DESC - Excludes range scans from the query plan.
Updated hints:
Hints
that specify table names have been expanded to accept Global Table
Hints. This allows a base table within a view to be specified using the
"view-name.table-name" syntax.
Hints
that specify index names have been expanded to accept Complex Index
Hints. This allows an index to be specified using the
"(table-name.column-name)" syntax instead of the index name.
Some hints can now optionally accept a query block parameter.
Renamed hints:
NO_PARALLEL - Formally NOPARALLEL.
NO_PARALLEL_INDEX - Formally NOPARALLEL_INDEX.
NO_REWRITE - Formally NOREWRITE.
Deprecated hints:
AND_EQUAL
HASH_AJ
MERGE_AJ
NL_AJ
HASH_SJ
NL_SJ
EXPAND_GSET_TO_UNION
ORDERED_PREDICATES
ROWID
STAR
Rule Based Optimizer Obsolescence
The
Rule Based Optimizer (RBO) is now obsolete in Oracle 10g. The
functionality is still present but no new functionality has been
included in it and it is no longer supported by Oracle. It is only
present to provide backwards compatibility during the migration to the
query optimizer (Cost Based Optimizer). The results of this osolescence
are:
The CHOOSE and RULE options for the OPTIMIZER_MODE parameter still exist but are no longer supported.
The default value for the OPTIMIZER_MODE parameter is ALL_ROWS.
The CHOOSE and RULE optimizer hints still exist but are no longer supported.
Code requiring the RBO must be migrated to use the query optimizer.
Tracing Enhancements
The Oracle Trace functionality has been removed from Oracle 10g. Instead the SQL Trace and TKPROF functionality should be used.
In
multi-tier environments where statements are passed to different
sessions by the application server it can become difficult to trace an
individual process from start to finish. To solve this problem Oracle
have introduced End to End Application Tracing which allows a client
process to be identified via the client identifier rather than the
typical session id. Each piece of trace information is linked to the
following information:
Client Identifier - Specifies the "real" end user. Set using the DBMS_SESSION.SET_IDENTIFIER procedure.
Service - Specifies a group of related applications. Created using the DBMS_SERVICE.CREATE_SERVICE procedure.
Module - Specifies a functional area or feature of an application. Set using the DBMS_APPLICATION_INFO.SET_MODULE procedure.
Action
- Specifies the current action (INSERT, UPDATE, DELETE etc.) within the
current module. Set using the DBMS_APPLICATION_INFO.SET_ACTION
procedure.
End
to end tracing can be managed via Enterprise Manager or a set of APIs
and views. Here are some examples of how to enable and disable to
various types of tracing:
BEGIN
-- Enable/Disable Client Identifier Trace.
Once
the trace files are produced the trcsess command line utility can be
used to filter out the relevant data from multiple files. The utility
accepts the following parameters:
OUTPUT - Specifies the name of the consolidated trace file.
SESSION - Consolidates the file based on the specified session id (SID.SERIAL# columns from V$SESSION).
CLIENT_ID - Consolidates the file based on the specified client identifier (CLIENT_IDENTIFIER column from V$SESSION).
SERVICE - Consolidates the file based on the specified service (SERVICE_NAME column from V$SESSION).
MODULE - Consolidates the file based on the specified module (MODULE column from V$SESSION).
ACTION - Consolidates the file based on the specified action (ACTION column from V$SESSION).
TRACE_FILES - A space separated list of trace files to be searched. If omitted all files in the local directory are searched.
At
lease one of the search criteria must be specified. If more than one is
specified only trace that matches all the criteria is consolidated.
Examples of trcsess usage are:
# Search all files for this session.
trcsess output=session.trc session=144.2274
# Search the specified files for this client identifier.
trcsess output=client.trc client_id=my_id db10g_ora_198.trc db10g_ora_206.trc
# Search the specified files for this service, module and action combination.
trcsess output=client.trc service=my_service module=my_module action=INSERT db10g_ora_198.trc db10g_ora_206.trc
Once the consolidated trace file is produced it can be processed by the TKPROF utility like any other SQL Trace file.
By
default statistics are gathered at the session level. The DBMS_MONITOR
package allows this to be altered to follow the client identifier,
service or combinations of the service, module and action:
BEGIN
The gathered statistics can be displayed using the following views:
DBA_ENABLED_AGGREGATIONS - Accumulated global statistics.
V$CLIENT_STATS - Accumulated statistics for the specified client identifier.
V$SERVICE_STATS - Accumulated statistics for the specified service.
V$SERV_MOD_ACT_STATS - Accumulated statistics for the specified service, module and action combination.
V$SVCMETRIC - Accumulated statistics for elapsed time of database calls and CPU usage.
SAMPLE Clause Enhancements
The
SAMPLE clause allows a query to return a limited sample of data by
specifying a percentage of rows or blocks to scan. This clause can now
be present in complex queries:
-- Query 10% or rows.
SELECT e.empno, e.ename, d.dname
FROM emp SAMPLE (10) e
JOIN dept d ON e.deptno = d.deptno;
-- Query 10% of blocks.
SELECT e.empno, e.ename, d.dname
FROM emp SAMPLE BLOCK (10) e
JOIN dept d ON e.deptno = d.deptno;
Hash Partitioned Global Indexes
Support
for hash partitioned global indexes has been added in Oracle 10g which
can improve performance when a small number of leaf blocks are
experiencing high levels of contention. The syntax for creating of a
hash paritioned global index is:
CREATE INDEX hgidx ON tab (c1,c2,c3) GLOBAL
PARTITION BY HASH (c1,c2)
(PARTITION p1 TABLESPACE tbs_1,
PARTITION p2 TABLESPACE tbs_2,
PARTITION p3 TABLESPACE tbs_3,
PARTITION p4 TABLESPACE tbs_4);
PL/SQL Enhancements in Oracle Database 10g
Oracle 10g includes many PL/SQL enhancements including:
PL/SQL Native Compilation
FORALL Support for Non-Consecutive Indexes
New IEEE Floating-Point Types
Improved Overloading With Numeric Types
Nested Table Enhancements
Compile-Time Warnings
Quoting Mechanism for String Literals
Implicit Conversion Between CLOB and NCLOB
Regular Expressions
Flashback Query Functions
UTL_COMPRESS
UTL_MAIL
PL/SQL Native Compilation
The
process of PL/SQL native compilation has been simplified in Oracle 10g.
The compiled shared libraries are now stored in the database and
extracted as necessary. This means they form part of the normal backup
and recovery process, require no manual maintenance and are available in
Real Application Cluster (RAC) configurations. Native compliation of
the package specification and body are independant of each other,
meaning either one, the other or both can be natively compiled.
The
PLSQL_NATIVE_LIBRARY_DIR parameter is the only one which must be set to
use native compilation. All other parameters have been obsoleted. The
associated compiler commands are stored in the
$ORACLE_HOME/plsql/spnc_commands file which should not need to be
modified.
Native
compilation is switched on and off using the PLSQL_CODE_TYPE parameter
which can be set at instance and session level using the ALTER SYSTEM
and ALTER SESSION commands respectively. The following is an example of
native PL/SQL compilation:
-- Set the PLSQL_NATIVE_LIBRARY_DIR parameter.
CONN / AS SYSDBA
ALTER SYSTEM SET PLSQL_NATIVE_LIBRARY_DIR='/u01/app/oracle/native/' SCOPE=SPFILE;
SHUTDOWN IMMEDIATE
STARTUP
-- Switch on native compilation and compile a procedure.
CONN scott/tiger
ALTER SESSION SET PLSQL_CODE_TYPE='NATIVE';
CREATE OR REPLACE PROCEDURE test_speed AS
v_number NUMBER;
BEGIN
FOR i IN 1 .. 10000000 LOOP
v_number := i / 1000;
END LOOP;
END;
/
SET TIMING ON
EXEC test_speed;
PL/SQL procedure successfully completed.
Elapsed: 00:00:07.19
-- Switch off native compilation and recompile the procedure.
ALTER SESSION SET PLSQL_CODE_TYPE='INTERPRETED';
ALTER PROCEDURE test_speed COMPILE;
EXEC test_speed;
PL/SQL procedure successfully completed.
Elapsed: 00:00:08.03
-- Clean up.
DROP PROCEDURE test_speed;
FORALL Support for Non-Consecutive Indexes
Oracle
10g introduces support for the FORALL syntax with non-consecutive
indexes in collections. The INDICES OF clause allows the FORALL syntax
to be used with sparse collections, while the VALUE OF clause is used
for collections of indexes pointing to other collections. The following
are examples of their usage:
/
New IEEE Floating-Point Types
Oracle
10g introduces the new IEEE floating-point types BINARY_FLOAT and
BINARY_DOUBLE. The types are extremely efficient for heavy floating
point computations as the work is passed directly to the operating
system. Literal assignments can be perfomed using the "f" and "d"
suffixes or conversion functions TO_BINARY_FLOAT and TO_BINARY_DOUBLE:
DECLARE
l_binary_float BINARY_FLOAT;
l_binary_double BINARY_DOUBLE;
BEGIN
l_binary_float := 1.1f;
l_binary_double := 1.00001d;
l_binary_float := TO_BINARY_FLOAT(1.1);
l_binary_double := TO_BINARY_DOUBLE(1.00001);
END;
/
Rather than raise exceptions, the resulting values of computations may equate to the following constants that can be tested for:
[BINARY_FLOAT|BINARY_DOUBLE]_NAN
[BINARY_FLOAT|BINARY_DOUBLE]_INFINITY
[BINARY_FLOAT|BINARY_DOUBLE]_MAX_NORMAL
[BINARY_FLOAT|BINARY_DOUBLE]_MIN_NORMAL
[BINARY_FLOAT|BINARY_DOUBLE]_MAX_SUBNORMAL
[BINARY_FLOAT|BINARY_DOUBLE]_MIN_SUBNORMAL
The constants for NaN and infinity are also available in SQL.
Improved Overloading With Numeric Types
Oracle 10g includes improved overloading of numeric types like:
-- Create package specification.
CREATE OR REPLACE PACKAGE numeric_overload_test AS
PROCEDURE go (p_number NUMBER);
PROCEDURE go (p_number BINARY_FLOAT);
PROCEDURE go (p_number BINARY_DOUBLE);
END;
/
-- Create package body.
CREATE OR REPLACE PACKAGE BODY numeric_overload_test AS
PROCEDURE go (p_number NUMBER) AS
BEGIN
DBMS_OUTPUT.put_line('Using NUMBER');
END;
PROCEDURE go (p_number BINARY_FLOAT) AS
BEGIN
DBMS_OUTPUT.put_line('Using BINARY_FLOAT');
END;
PROCEDURE go (p_number BINARY_DOUBLE) AS
BEGIN
DBMS_OUTPUT.put_line('Using BINARY_DOUBLE');
END;
END;
/
-- Test it.
SET SERVEROUTPUT ON
BEGIN
numeric_overload_test.go(10);
numeric_overload_test.go(10.1f);
numeric_overload_test.go(10.1d);
END;
/
It
is important to check that the correct overload is being used at all
times. The appropriate suffix or conversion function will make the
engine to pick the correct overload.
Nested Table Enhancements
Nested
tables in PL/SQL now support more operations than before. Collections
can be assigned directly to the value of another collection of the same
type, or to the result of a set expression:
SET SERVEROUTPUT ON
DECLARE
TYPE t_colors IS TABLE OF VARCHAR2(10);
l_col_1 t_colors := t_colors('Red', 'Green', 'Blue');
l_col_2 t_colors := t_colors('Red', 'Green', 'Yellow');
l_col_3 t_colors;
PROCEDURE display (p_text IN VARCHAR2,
p_col IN t_colors) IS
BEGIN
DBMS_OUTPUT.put_line(CHR(10) || p_text);
FOR i IN p_col.first .. p_col.last LOOP
DBMS_OUTPUT.put_line(p_col(i));
END LOOP;
END;
BEGIN
-- Basic assignment.
l_col_3 := l_col_1;
display('Direct Assignment:', l_col_3);
-- Expression assignments.
l_col_3 := l_col_1 MULTISET UNION l_col_2;
display('MULTISET UNION:', l_col_3);
l_col_3 := l_col_1 MULTISET UNION DISTINCT l_col_2;
display('MULTISET UNION DISTINCT:', l_col_3);
l_col_3 := l_col_1 MULTISET INTERSECT l_col_2;
display('MULTISET INTERSECT:', l_col_3);
l_col_3 := l_col_1 MULTISET INTERSECT DISTINCT l_col_2;
display('MULTISET INTERSECT DISTINCT:', l_col_3);
l_col_3 := l_col_1 MULTISET EXCEPT l_col_2;
display('MULTISET EXCEPT:', l_col_3);
l_col_3 := l_col_1 MULTISET EXCEPT DISTINCT l_col_2;
display('MULTISET EXCEPT DISTINCT:', l_col_3);
END;
/
Compile-Time Warnings
Oracle
can now produce compile-time warnings when code is ambiguous or
inefficient be setting the PLSQL_WARNINGS parameter at either instance
or session level. The categories ALL, SEVERE, INFORMATIONAL and
PERFORMANCE can be used to alter the type of warnings that are produced.
Examples of their usage include:
-- Instance and session level.
ALTER SYSTEM SET PLSQL_WARNINGS='ENABLE:ALL';
ALTER SESSION SET PLSQL_WARNINGS='DISABLE:PERFORMANCE';
Quoting Mechanism for String Literals
Oracle
10g allows you to define your own string delimiters to remove the need
to double up any single quotes. Any character that is not present in the
string can be used as the delimeter:
SET SERVEROUTPUT ON
BEGIN
-- Orginal syntax.
DBMS_OUTPUT.put_line('This is Tim''s string!');
-- New syntax.
DBMS_OUTPUT.put_line(q'#This is Tim's string!#');
DBMS_OUTPUT.put_line(q'[This is Tim's string!]');
END;
/
This is Tim's string!
This is Tim's string!
This is Tim's string!
PL/SQL procedure successfully completed.
Implicit Conversion Between CLOB and NCLOB
Oracle
10g now supports implicit conversions between CLOBs and NCLOBs and
vice-versa. As with all type conversions it is still better to be
explicit and use the conversion functions TO_CLOB and TO_NCLOB for
clarity.
Regular Expressions
Oracle 10g supports regular expressions in SQL and PL/SQL with the following functions:
REGEXP_INSTR - Similar to INSTR except it uses a regular expression rather than a literal as the search string.
REGEXP_LIKE - Similar to LIKE except it uses a regular expression as the search string.
REGEXP_REPLACE - Similar to REPLACE except it uses a regular expression as the search string.
REGEXP_SUBSTR - Returns the string matching the regular expression. Not really similar to SUBSTR.
/
Building regular expressions to match your requirements can get a little confusing and this is beyond the scope of this article.
Flashback Query Functions
The TIMESTAMP_TO_SCN and SCN_TO_TIMESTAMP functions have been added to SQL and PL/SQL to simplify flashback operations:
SELECT *
FROM emp AS OF SCN TIMESTAMP_TO_SCN(SYSTIMESTAMP - 1/24);
SELECT *
FROM emp AS OF TIMESTAMP SCN_TO_TIMESTAMP(993240);
DECLARE
l_scn NUMBER;
l_timestamp TIMESTAMP;
BEGIN
l_scn := TIMESTAMP_TO_SCN(SYSTIMESTAMP - 1/24);
l_timestamp := SCN_TO_TIMESTAMP(l_scn);
END;
/
UTL_COMPRESS
The
UTL_COMPRESS package provides an API to allow compression and
decompression of binary data (RAW, BLOB and BFILE). It uses the
Lempel-Ziv compression algorithm which is equivalent to functionality of
the gzip utility. A simple example of it's usage would be:
/
UTL_MAIL
The
UTL_MAIL package provides a simple API to allow email to be sent from
PL/SQL. In prior versions this was possible using the UTL_SMTP package,
but this required knowledge of the SMTP protocol.
The package is loaded by running the following scripts:
CONN sys/password AS SYSDBA
@$ORACLE_HOME/rdbms/admin/utlmail.sql
@$ORACLE_HOME/rdbms/admin/prvtmail.plb
In addition the SMTP_OUT_SERVER parameter must be set to identify the SMTP server:
CONN sys/password AS SYSDBA
ALTER SYSTEM SET smtp_out_server='smtp.domain.com' SCOPE=SPFILE;
SHUTDOWN IMMEDIATE
STARTUP
With the configuration complete we can now send a mail using:
BEGIN
UTL_MAIL.send(sender => ' me@domain.com',
subject => 'UTL_MAIL Test',
message => 'If you get this message it worked!');
END;
/
The package also supports sending mails with RAW and VARCHAR2 attachments.
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