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TABLE OF CONTENTS
-----------------
0. Introduction and Terminology
1. Configuration
1.1. Database space Requirements
1.2. Installing the Tool
1.3. Errors during Installation
2. Gathering data - taking a snapshot
2.1. Automating Statistics Gathering
2.2. Using dbms_job
3. Running a Performance report
3.1. Running the report
3.2. Gathering optimizer statistics on the PERFSTAT schema
4. Configuring the amount of data captured
4.1. Snapshot Level
4.2. Snapshot SQL thresholds
4.3. Changing the default values
4.4. Snapshot Levels - details
4.5. Specifying a Session Id
4.6. Input Parameters for the SNAP and
MODIFY_STATSPACK_PARAMETERS procedures
5. Time Units used for Wait events
6. Event Timings
7. Managing and Sharing performance data
7.1. Sharing data via export
7.2. Purging/removing unnecessary data
7.3. Removing all data
8. New and Changed Features
9. Upgrading from earlier releases
10. OPS specific considerations
11. Conflicts and differences compared to UTLBSTAT/UTLESTAT
11.1. Running BSTAT/ESTAT in conjunction to Statspack
11.2. Differences between Statspack and BSTAT/ESTAT
12. Removing the package
13. Supplied Scripts Overview
14. Limitations and Modifications
14.1. Limitations
14.2. Modifications
0. Introduction
----------------
To effectively perform reactive tuning, it is vital to have an established
baseline for later comparison when the system is running poorly. Without
a baseline data point, it becomes very difficult to identify what the new
problem is attributable to: Has the volume of transactions on the system
increased? Has the transaction profile or application changed? Has the
number of users increased?
Statspack fundamentally differs from the well known UTLBSTAT/UTLESTAT
tuning scripts by collecting more information, and also by storing the
performance statistics data permanently in Oracle tables, which can later
be used for reporting and analysis. The data collected can be analyzed
using the report provided, which includes an "instance health and load"
summary page, high resource SQL statements, as well as the traditional
wait events and initialization parameters.
Statspack improves on the existing UTLBSTAT/UTLESTAT performance scripts
in the following ways:
- Statspack collects more data, including high resource SQL
- Statspack pre-calculates many ratios useful when performance
tuning, such as cache hit ratios, per transaction and per
second statistics (many of these ratios must be calculated
manually when using BSTAT/ESTAT)
- Permanent tables owned by PERFSTAT store performance statistics;
instead of creating/dropping tables each time, data is inserted
into the pre-existing tables. This makes historical data
comparisons easier
- Statspack separates the data collection from the report generation.
Data is collected when a 'snapshot' is taken; viewing the data
collected is in the hands of the performance engineer when he/she
runs the performance report
- Data collection is easy to automate using either dbms_job or an
OS utility
NOTE: The term 'snapshot' is used to denote a set of statistics gathered
at a single time, identified by a unique Id which includes the
snapshot number (or snap_id). This term should not be confused
with Oracle's Snapshot Replication technology.
How does STATSPACK work?
Statspack is a set of SQL, PL/SQL and SQL*Plus scripts which allow the
collection, automation, storage and viewing of performance data. A user
is automatically created by the installation script - this user, PERFSTAT,
owns all objects needed by this package. This user is granted limited
query-only privileges on the V$views required for performance tuning.
Statspack users will become familiar with the concept of a 'snapshot'.
'snapshot' is the term used to identify a single collection of
performance data. Each snapshot taken is identified by a 'snapshot id'
which is a unique number generated at the time the snapshot is taken;
each time a new collection is taken, a new snap_id is generated.
The snap_id, along with the database identifier (dbid) and instance number
(instance_number) comprise the unique key for a snapshot (using this
unique combination allows storage of multiple instances of an OPS
database in the same tables).
Once snapshots are taken, it is possible to run the performance report.
The performance report will prompt for the two snapshot id's the report
will process. The report produced calculates the activity on the instance
between the two snapshot periods specified, in a similar way to the
BSTAT/ESTAT report; to compare - the first snap_id supplied can be
considered the equivalent of running BSTAT; the second snap_id
specified can be considered the equivalent of ESTAT. Unlike BSTAT/ESTAT
which can by it's nature only compare two static data points, the report
can compare any two snapshots specified.
1. Configuration
-----------------
1.1. Database Space Requirements
The amount of database space required by the package will vary considerably
based on the frequency of snapshots, the size of the database and instance,
and the amount of data collected (which is configurable).
It is therefore difficult to provide general storage clauses and space
utilization predictions which will be accurate at each site.
Note: The default initial and next extent size is 1MB or 5MB for all
tables and indexes which contain changeable data. The minimum
default tablespace requirement is approximately 45MB.
Dictionary Managed Tablespaces
If you install the package in a dictionary-managed tablespace, Oracle
suggests you monitor the space used by the objects created, and adjust
the storage clauses of the segments, if required.
Locally Managed Tablespaces
If you install the package in a locally-managed tablespace, storage
clauses are not required, as the storage characteristics are
automatically managed.
1.2 Installing the Tool
Step 1.
This step creates the PERFSTAT user, which will own all PL/SQL code and
database objects created (including the STATSPACK tables, constraints
and the STATSPACK package).
During the installation you will be prompted for the PERFSTAT
user's default and temporary tablespaces.
The default tablespace will be used to create all Statspack
objects (such as tables and indexes). The temporary tablespace
will be used for sort-type activities (for more information on
temporary tablespaces, see the Oracle Concepts Documentation).
NOTE:
o Oracle do not recommend using the SYSTEM tablespace to store
statistics data. A more appropriate tablespace is the TOOLS
tablespace.
Similarly, do not use the SYSTEM tablespace as the Statspack
user's TEMPORARY tablespace.
o During the installation, the dbms_shared_pool and dbms_job
PL/SQL packages are created. dbms_shared_pool is used to
pin the Statspack package in the shared pool; dbms_job
is created on the assumption the DBA will want to schedule
periodic snapshots automatically using dbms_job.
To install the package, either change directory to the ORACLE_HOME
rdbms/admin directory, or fully specify the ORACLE_HOME/rdbms/admin
directory when calling the installation script, spcreate.
To run the installation script, you must use SQL*Plus and connect as
a user with SYSDBA privilege. Do not use Server Manager (svrmgrl)
to install Statspack, as the installation will fail.
e.g. Start SQL*Plus, then:
on Unix:
SQL> connect / as sysdba
SQL> @?/rdbms/admin/spcreate
on NT:
SQL> connect / as sysdba
SQL> @%ORACLE_HOME%\rdbms\admin\spcreate
The spcreate install script runs 3 other scripts - you do not need to
run these - the scripts are called automatically:
1. spcusr -> creates the user and grants privileges
2. spctab -> creates the tables
3. spcpkg -> creates the package
Check each of the three output files produced (spcusr.lis,
spctab.lis, spcpkg.lis) by the installation to ensure no
errors were encountered, before continuing on to the next step.
Note that there are two ways to install Statspack - interactively (as
shown above), or in "batch" mode; batch mode is useful when you do
not wish to be prompted for the PERFSTAT user's default and
temporary tablespaces.
Batch mode installation
~~~~~~~~~~~~~~~~~~~~~~~
To install in batch mode, you must assign values to the SQL*Plus
variables which specify the default and temporary tablespaces before
running spcreate.
The variables are:
default_tablespace -> for the default tablespace
temporary_tablespace -> for the temporary tablespace
e.g.
on Unix:
SQL> connect / as sysdba
SQL> define default_tablespace='tools'
SQL> define temporary_tablespace='temp'
SQL> @?/rdbms/admin/spcreate
spcreate will no longer prompt for the above information.
Step 2.
The setup phase is now complete.
If you wish to, you may decide to change the password of the
PERFSTAT user for security purposes.
1.3 Errors during installation
A common error made during Statspack installation is running the install
script from Server Manager (svrmgrl) rather than from SQL*Plus. If you
use svrmgrl, the installation will fail. To correctly install Statspack
after such errors, first run the de-install script, then the install
script. Both scripts must be run from SQL*Plus.
e.g. Start SQL*Plus, connect as a user with SYSDBA privilege, then:
SQL> @spdrop
SQL> @spcreate
2. Gathering data - taking a snapshot
---------------------------------------
The simplest interactive way to take a snapshot is to login to SQL*Plus
as the PERFSTAT user, and execute the procedure statspack.snap:
e.g.
SQL> connect perfstat/perfstat
SQL> execute statspack.snap;
Note: In an OPS environment, you must connect to the instance
you wish to collect data for.
This will store the current values for the performance statistics
in the STATSPACK tables, and can be used as a baseline snapshot
for comparison with another snapshot taken at a later time.
For better performance analysis, set the init.ora parameter timed_statistics
to true; this way, Statspack data collected will include important timing
information. The timed_statistics parameter is also dynamically changable
using the 'alter system' command. Timing data is important and is usually
required by Oracle support to diagnose performance problems.
2.1 Automating statistics gathering
To be able to make comparisons of performance from one day, week or
year to the next, there must be multiple snapshots taken over a period
of time.
The best method to gather snapshots is to automate the collection on
a regular time interval. It is possible to do this:
- within the database, using the Oracle dbms_job procedure to
schedule the snapshots
- using Operating System utlities (such as 'cron' on Unix or 'at' on
NT) to schedule the snapshot
2.2. Using dbms_job
To use an Oracle-automated method for collecting statistics, you can use
dbms_job. A sample script on how to do this is supplied in spauto.sql,
which schedules a snapshot every hour, on the hour.
You may wish to schedule snapshots at regular times each day to reflect your
system's OLTP and/or batch peak loads. For example take snapshots at 9am,
10am, 11am, 12 midday and 6pm for the OLTP load, then a snapshot at
12 midnight and another at 6am for the batch window.
In order to use dbms_job to schedule snapshots, the job_queue_processes
initialization parameter must be set to greater than 0 in the init.ora
file for the job to be run automatically.
Example of an init.ora entry:
# Set to enable the job queue process to start. This allows dbms_job
# to schedule automatic statistics collection using STATSPACK
job_queue_processes=1
If using spauto.sql in OPS enviroment, the spauto.sql script must
be run once on each instance in the cluster. Similarly, the
job_queue_processes parameter must also be set for each instance.
Changing the interval of statistics collection
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
To change the interval of statistics collection use the dbms_job.interval
procedure
e.g.
execute dbms_job.interval(1,'SYSDATE+(1/48)');
Where 'SYSDATE+(1/48)' will result in the statistics being gathered each
1/48 hours (i.e. every half hour).
To force the job to run immediately,
execute dbms_job.run(<job number> ;
To remove the autocollect job,
execute dbms_job.remove(<job number>;
For more information on dbms_job, see the Supplied Packages Reference
Manual.
3. Running a Performance report
---------------------------------
Once snapshots are taken, it is possible to generate a performance report.
The SQL script which generates the report prompts for the two snapshot id's
to be processed.
The first will be the beginning snapshot id, the second will be the
ending snapshot id. The report will then calculate and print ratios,
increases etc. for all statistics between the two snapshot periods, in
a similar way to the BSTAT/ESTAT report.
Note: It is not correct to specify begin and end snapshots where the
begin snapshot and end snapshot were taken from different
instance startups. In other words, the instance must not have
been shutdown between the times that the begin and end snapshots
were taken.
The reason for this requirement is the database's dynamic
performance tables which Statspack queries to gather the data
are memory resident, hence shutting down the database will
reset the values in the performance tables to 0. As Statspack
subtracts the begin-snapshot statistics from the end-snapshot
statistics, the resulting output will be invalid.
If begin and end snapshots which were taken between shutdowns
are specified in the report, the report shows an appropriate error
to indicate this.
Separating the phase of data gathering from producing a report, allows the
flexibility of basing a report on any data points selected. For example
it may be reasonable for the DBA to use the supplied automation script to
automate data collection every hour on the hour; If at some later point
a performance issue arose which may be better investigated by looking
at a three hour data window rather than an hour's worth of data, the
only thing the DBA need do, is specify the required start point and end
point when running the report.
3.1 Running the report
To examine the change in statistics between two time periods, the
spreport.sql file is executed while being connected to the PERFSTAT
user. The spreport.sql command file is located in the rdbms/admin
directory of the Oracle Home.
Note: In an OPS environment you must connect to the instance you
wish to report on.
You will be prompted for:
1. The beginning snapshot Id
2. The ending snapshot Id
3. The name of the report text file to be created
e.g. on Unix
SQL> connect perfstat/perfstat
SQL> @?/rdbms/admin/spreport
e.g. on NT
SQL> connect perfstat/perfstat
SQL> @%ORACLE_HOME%\rdbms\admin\spreport
Example output:
SQL> connect perfstat/perfstat
Connected.
SQL> @spreport
DB Id DB Name Inst Num Instance
----------- ------------ -------- ------------
2618106428 PRD1 1 prd1
Completed Snapshots
Snap Snap
Instance DB Name Id Snap Started Level Comment
------------ ------------ ----- ----------------- ----- ----------------------
prd1 PRD1 1 11 May 2000 12:07 5
2 11 May 2000 12:08 5
Specify the Begin and End Snapshot Ids
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enter value for begin_snap: 1
Begin Snapshot Id specified: 1
Enter value for end_snap:
End Snapshot Id specified: 2
Specify the Report Name
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is sp_1_2 To use this name,
press <return> to continue, otherwise enter an alternative.
Enter value for report_name: <press return or enter a new name>
Using the report name sp_1_2
The report will now scroll past, and also be written to the file
specified (e.g. sp_1_2.lis).
Batch mode report generation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
To run a report without being prompted, assign values to the
SQL*Plus variables which specify the begin snap id, the end snap id
and the report name before running spreport.
The variables are:
begin_snap -> specifies the begin Snapshot Id
end_snap -> specifies the end Snapshot Id
report_name -> specifies the Report output name
e.g.
on Unix:
SQL> connect perfstat/perfstat
SQL> define begin_snap=1
SQL> define end_snap=2
SQL> define report_name=batch_run
SQL> @?/rdbms/admin/spreport
spreport will no longer prompt for the above information.
3.2. Gathering Optimizer statistics on the PERFSTAT schema
For best performance when running spreport, collect optimizer statistics
for tables and indexes owned by the PERFSTAT. This should be performed
whenever significant change in data volumes in PERFSTAT's tables.
The easiest way to do this, is either to use dbms_utility, or dbms_stats,
and specify the PERFSTAT user:
execute dbms_utility.analyze_schema('PERFSTAT','COMPUTE');
or
execute dbms_stats.gather_schema_stats('PERFSTAT');
4. Configuring the amount of data captured
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4.1. Snapshot Level
It is possible to change the amount of information gathered by the package,
by specifying a different snapshot 'level'. In other words, the level
chosen (or defaulted) will decide the amount of data collected.
The higher the snapshot level, the more data is gathered. The default
level set by the installation is level 5. The various levels are
explained in detail section 4.4 below.
4.2. Snapshot SQL thresholds
There are other parameters which can be configured in addition to the
snapshot level.
These parameters are used as thresholds when collecting data on SQL
statements; data will be captured on any SQL statements that breach
the specified thresholds.
Snapshot level and threshold information used by the package is stored
in the stats$statspack_parameter table.
4.3. Changing the default values for Snapshot Level and SQL Thresholds
If you wish to, you can change the default parameters used for taking
snapshots, so that they are tailored to the instance's workload.
You can do this either by:
o Taking a snapshot, and specifying the new defaults to be saved to the
database (using statspack.snap, and using the i_modify_parameter
input variable).
SQL> execute statspack.snap -
(i_snap_level=>10, i_modify_parameter=>'true');
Setting the i_modify_parameter value to true will save the new
thresholds in the stats$statspack_parameter table; these thresholds
will be used for all subsequent snapshots.
If the i_modify_parameter was set to false or if it were omitted, the
new parameter values would not be saved. Only the snapshot taken at
that point will use the specified values, any subsequent snapshots will
use the preexisting values in the stats$statspack_parameter table.
The full list of parameters which can be passed into snap
are listed in 4.6. below
o Changing the defaults immediately without taking a snapshot, using the
statspack.modify_statspack_parameter procedure. For example to change
the snapshot level to 10, and the SQL thresholds for buffer_gets and
disk_reads, the following statement can be issued:
SQL> execute statspack.modify_statspack_parameter -
(i_snap_level=>10, i_buffer_gets_th=>10000, i_disk_reads_th=>1000);
This procedure changes the values permananently, but does not
take a snapshot.
The full list of parameters which can be passed into the
modify_statspack_parameter procedure are the same as those for
the snap procedure. These are listed in 4.6. below.
4.4 Snapshot Levels - details
Levels >= 0 General performance statistics
Statistics gathered:
This level and any level greater than 0 collects general
performance statistics, such as: wait statistics, system events,
system statistics, rollback segment data, row cache, SGA,
background events, session events, lock statistics,
buffer pool statistics, parent latch statistics.
Levels >= 5 Additional data: SQL Statements
This level includes all statistics gathered in the lower level(s),
and additionally gathers the performance data on high resource
usage SQL statements.
In a level 5 snapshot, note that the time required for the snapshot
to complete is dependant on the shared_pool_size and on the number of
SQL statements in the shared pool at the time the snapshot is taken:
the larger the shared pool, the longer the time taken to complete
the snapshot.
SQL 'Thresholds'
The SQL statements gathered by Statspack are those which exceed one of
four predefined threshold parameters:
- number of executions of the SQL statement (default 100)
- number of disk reads performed by the SQL statement (default 1,000)
- number of parse calls performed by the SQL statement (default 1,000)
- number of buffer gets performed by the SQL statement (default 10,000)
- size of sharable memory used by the SQL statement (default 1m)
- version count for the SQL statement (default 20)
The values of each of these threshold parameters are used when
deciding which SQL statements to collect - if a SQL statement's
resource usage exceeds any one of the above threshold values, it
is captured during the snapshot.
The SQL threshold levels used are either those stored in the table
stats$statspack_parameter, or by the thresholds specified when
the snapshot is taken.
Levels >= 10 Additional statistics: Parent and Child latches
This level includes all statistics gathered in the lower levels, and
additionally gathers Parent and Child Latch information. Data gathered
at this level can sometimes cause the snapshot to take longer to complete
i.e. this level can be resource intensive, and should only be used
when advised by Oracle personnel.
4.5. Specifying a Session Id
If you would like to gather session statistics and wait events for a
particular session (in addition to the instance statistics and wait events),
it is possible to specify the session id in the call to Statspack. The
statistics gathered for the session will include session statistics,
session events and lock activity. The default behaviour is to not to
gather session level statistics.
SQL> execute statspack.snap(i_session_id=>3);
4.6. Input Parameters for the SNAP and MODIFY_STATSPACK_PARAMETERS procedures
Parameters able to be passed in to the statspack.snap and
statspack.modify_statspack_parameter procedures are as follows:
Range of Default
Parameter Name Valid Values Value Meaning
------------------ ------------ ------- -----------------------------------
i_snap_level 0, 5, 10 5 Snapshot Level
i_ucomment Text Blank Comment to be stored with Snapshot
i_executions_th Integer >=0 100 SQL Threshold: number of times
the statement was executed
i_disk_reads_th Integer >=0 1,000 SQL Threshold: number of disk reads
the statement made
i_parse_calls_th Integer >=0 1,000 SQL Threshold: number of parse
calls the statement made
i_buffer_gets_th Integer >=0 10,000 SQL Threshold: number of buffer
gets the statement made
i_sharable_mem_th Integer >=0 1048576 SQL Threshold: amount of sharable
memory
i_version_count_th Integer >=0 20 SQL Threshold: number of versions
of a SQL statement
i_session_id Valid sid 0 (no Session Id of the Oracle Session
from session) to capture session granular
v$session statistics for
i_modify_parameter True, False False Save the parameters specified for
future snapshots? |
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