Subject:How to Perform a Healthcheck on theDatabaseDoc ID: Note:122669.1 Type: BULLETIN Last Revision Date: 20-MAR-2008 Status: PUBLISHEDTable of Contents-----------------1. Introduction2. Parameter file3. Controlfiles4. Redolog files5. Archiving6. Datafiles6.1 Autoextend6.2 Location7. Tablespaces7.1 SYSTEM Tablespace7.2 SYSAUX Tablespace7.3 Locally vs Dictionary Managed Tablespaces7.4 Temporary Tablespace7.5 Tablespace Fragmentation8. Objects8.1 Number of Extents8.2 Next extent8.3 Indexes9. AUTO vs MANUAL undo9.1 AUTO Undo9.2 Manual undo10. Memory Management10.1 Pre-Oracle 9i10.2 Oracle 9i10.3 Oracle 10g10.4 Oracle 11g11. Logging & Tracing11.1 Alert File11.2 Max_dump_file_size11.3 User and core dump size parameters11.4 Audit files11.5 Sqlnet1. Introduction---------------This article explains how to perform a health check on the database. General guidelines are given on what areas to investigate to get a better overview onhow the database is working and evolving. These guidelines will reveal common issues regarding configuration as well as problems that may occur in the future.The areas investigated here are mostly based on scripts and are brought to you without any warranty, these scripts may need to be adapted for next database releases and features. This article will probably need to be extended to serve specific application needs/checks.Although some performance areas are discussed in this article, it is not the intention of this article to give a full detailed explanation of optimizing the database performance.General scripts that help track information on the database:=)> Note 250262.1 Health Check / Validation Engine Guide=)> Note 136697.1“hcheck8i.sql” script to check for known problems in Oracle8i, Oracle9i, and Oracle10g2. Parameter file-----------------The parameter file can exists in 2 forms. First of all we have the text-based version, commonly referred to as init.ora or pfile, and a binary-based file, commonly referred to as spfile. The pfile can be adjusted using a standard Operating System editor, while the spfile needs to be managed through the instance itself.It is important to realize that the spfile takes presedence above the pfile, meaning whenever there is an spfile available this will be automatically taken unless specified otherwise.NOTE: Getting an RDA report after making changes to the database configuration is also a recommendation. Keeping historical RDA reports will ensure you havean overview of the database configuration as the database evolves.Reference:Note 249664.1: Pfile vs SPfile3. Controlfiles---------------It is highly recommended to have at least two copies of the controlfile. This can be done by mirroring the controlfile, strongly recommended on different physicaldisks. If a controlfile is lost, due to a disk crash for example, then you canuse the mirrored file to startup the database. In this way fast and easy recovery from controlfile loss is obtained.connect as sysdbaSQL> select status, name from v$controlfile;STATUS NAME------- ---------------------------------/u01/oradata/L102/control01.ctl/u02/oradata/L102/control02.ctlThe location and the number of controlfiles can be controlled by the 'control_files' initialization parameter.4. Redolog files----------------The Oracle server maintains online redo log files to minimize loss of data in the database. Redo log files are used in a situation such as instance failure to recover commited data that has not yet been written to the data files. Mirroring theredo log files, strongly recommended on different physical disks, makes recovery more easy in case one of the redo log files is lost due to a disk crash, user delete, etc.connect as sysdbaSQL> select * from v$logfile;GROUP# STATUS TYPE MEMBER--------- ------- ------ -----------------------------------1 ONLINE /u01/oradata/L102/redo01_A.log1 ONLINE /u02/oradata/L102/redo01_B.log2 ONLINE /u01/oradata/L102/redo02_A.log2 ONLINE /u02/oradata/L102/redo02_B.log3 ONLINE /u01/oradata/L102/redo03_A.log3 ONLINE /u02/oradata/L102/redo03_B.logAt least two redo log groups are required, although it is advisable to have at least three redo log groups when archiving is enabled (see the following chapter). It is common, in environments where there are intensive log switches, to see the ARCHiver background process fall behind of the LGWR background process. In this case the LGWRprocess needs to wait for the ARCH process to complete archiving the redo log file.References :Note 102995.1 Maintenance of Online Redo Log Groups and Members5. Archiving------------Archiving provides the mechanism needed to backup the changes of the database.The archive files are essential in providing the necessary information to recover the database. It is advisable to run the database in archive log mode, although you may have reasons for not doing this, for example in case of a TEST environment where you accept to loose the changes made between the current time and the last backup.You may ignore this chapter when the database doesn't run in archive log mode.There are several ways of checking the archive configuration, below is one of them:connect as sysdbaSQL> archive log listDatabase log mode No Archive Mode --OR-- Archive ModeAutomatic archival Disabled --OR-- EnabledArchive destination <arch. dest.> --OR-- USE_DB_RECOVERY_FILE_DESTOldest online log sequence seq. noCurrent log sequence seq. noPre-10g, if the database is running in archive log mode but the automatic archiver process is disabled, then you were required to manually archive the redolog files. If this is not done in time then the database is frozen and any activity is prevented. Therefore you should enable automatic archiving when the database is running in archive log mode. This can be done by setting the 'log_archive_start' parameter to true in the parameter file.Starting from 10g, this parameter became obsolete and is no longer required to be set explicitly. It is important that there is enough free space on the dedicated disk(s) for the archive files, otherwise the ARCHiver process can't write and a crash is inevitable.References:Note 69739.1 How to Turn Archiving ON and OFFNote 122555.1 Determine how many disk space is needed for the archive files6. Datafiles------------6.1 Autoextend~~~~~~~~~~~~~~~The autoextend command option enables or disables the automatic extension ofdata files. If the given datafile is unable to allocate the space needed, itcan increase the size of the datafile to make space for objects to grow.A standard Oracle datafile can have, at most, 4194303 Oracle datablocks.So this also implies that the maximum size is dependant on the Oracle Block size used.DB_BLOCK_SIZE Max Mb value to use in any command~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~2048 8191 M4096 16383 M8192 32767 M16384 65535 Mstarting from Oracle 10g, we have a new functionality called BIGFILE, whichallows for bigger files to be created. Please also consider that every Operating System has its limits, therefore you should make sure that the maximum size ofa datafile cannot be extended past the Operating System allowed limit.To determine if a datafile and thus, a tablespace, has AUTOEXTEND capabilities:SQL> select file_id, tablespace_name, bytes, maxbytes, maxblocks, increment_by, file_namefrom dba_data_fileswhere autoextensible = 'YES';Reference:Note 112011.1: ALERT: RESIZE or AUTOEXTEND can "Over-size" Datafiles and Corrupt the DictionaryNote 262472.1: 10g BIGFILE Type Tablespaces Versus SMALLFILE Type6.2 Location~~~~~~~~~~~~~Verify the location of your datafiles. Overtime a database will grow and datafiles may be added to the database. Avoid placing datafiles on a 'wherever there is space' basis as this will complicate backup strategies and maintenance.Below is an example of bad usage:SQL> select * from v$dbfile;FILE# NAME--------- --------------------------------------------------1 D:\DATABASE\SYS1D806.DBF2 D:\DATABASE\D806\RBS1D806.DBF3 D:\DATABASE\D806\TMP1D806.DBF5 D:\DATABASE\D806\USR1D806.DBF6 D:\USR2D806.DBF7 F:\ORACLE\USR3D806.DBF7. Tablespaces--------------7.1 SYSTEM Tablespace~~~~~~~~~~~~~~~~~~~~~~User objects should not be created in the system tablespace. Doing so can lead to unnecessary fragmentation and preventing system tables of growing. The following queryreturns a list of objects that are created in the system tablespace but not owned by SYS or SYSTEM.SQL> select owner, segment_name, segment_typefrom dba_segmentswhere tablespace_name = 'SYSTEM'and owner not in ('SYS','SYSTEM');7.2 SYSAUX Tablespace (10g Release and above)~~~~~~~~~~~~~~~~~~~~~~The SYSAUX tablespace was automatically installed as an auxiliary tablespace to the SYSTEM tablespace when you created or upgraded the database. Some database components that formerly created and used separate tablespaces now occupy theSYSAUX tablespace.If the SYSAUX tablespace becomes unavailable, core database functionality will remain operational. The database features that use the SYSAUX tablespace could fail, or function with limited capability.The amount of data stored in this tablespace can be significant and may growover time to unmanageble sizes if not configured properly. There are a fewcomponents that need special attention.To check which components are occupying space:select space_usage_kbytes, occupant_name, occupant_descfrom v$sysaux_occupantsorder by 1 desc;Reference:Note 329984.1: Usage and Storage Management of SYSAUX tablespace occupants SM/AWR, SM/ADVISOR, SM/OPTSTAT and SM/OTHER7.3 Locally vs Dictionary Managed Tablespaces~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Locally Managed Tablespaces are available since Oracle 8i, however they becamethe default starting from Oracle 9i. Locally Managed Tablespaces, also referred to as LMT, have some advantage over Data Dictionary managed tablespaces.To verify which tablespace is Locally Managed or Dictionary Managed, you can run the following query:SQL> select tablespace_name, extent_managementfrom dba_tablespaces;Reference:Note 93771.1: Introduction to Locally-Managed TablespacesNote 105120.1: Advantages of Using Locally Managed vs Dictionary Managed Tablespaces7.4 Temporary Tablespace~~~~~~~~~~~~~~~~~~~~~~~~~o Locally Managed Tablespaces use tempfiles to serve the temporary tablespace, whereas Dictionary Managed Tablespaces use a tablespace of the type temporary. When you are running an older version (pre Oracle 9i), then it is important to check the type of tablespace used to store the temporary segments. By default, all tablespaces are created as PERMANENT, therefore you should make sure that the tablespace dedicated for temporary segments is of the type TEMPORARY.SQL> select tablespace_name, contentsfrom dba_tablespaces;TABLESPACE_NAME CONTENTS------------------------------ ---------SYSTEM PERMANENTUSER_DATA PERMANENTROLLBACK_DATA PERMANENTTEMPORARY_DATA TEMPORARYo Make sure that the users on the database are assigned a tablespace of thetype temporary. The following query lists all the users that have a permanent tablespace specified as their default temporary tablespace.SQL> select ername, t.tablespace_namefrom dba_users u, dba_tablespaces twhere u.temporary_tablespace = t.tablespace_nameand t.contents <> 'TEMPORARY';Note: User SYS and SYSTEM will show the SYSTEM tablespace as there defaulttemporary tablespace. This value can be altered as well to prevent fragmentation in the SYSTEM tablespace.SQL> alter user SYSTEM temporary tablespace TEMP;o The space allocated in the temporary tablespace is reused. This is done forperformance reasons to avoid the bottleneck of constant allocating and de-allocating of extents and segments. Therefore when looking at the free space in the temporary tablespace, this may appear as full all the time. The following are a few queries that can be used to list more meaningful information about the temporary segment usage:This will give the size of the temporary tablespace:SQL> select tablespace_name, sum(bytes)/1024/1024 mbfrom dba_temp_filesgroup by tablespace_name;This will give the "high water mark" of that temporary tablespace (= max used at one time):SQL> select tablespace_name, sum(bytes_cached)/1024/1024 mbfrom v$temp_extent_poolgroup by tablespace_name;This will give current usage:SQL> select ss.tablespace_name,sum((ed_blocks*ts.blocksize))/1024/1024 mb from gv$sort_segment ss, sys.ts$ tswhere ss.tablespace_name = group by ss.tablespace_name;7.5 Tablespace Fragmentation~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Heavly fragmented tablespaces can have an impact on the performance, especially when a lot of Full Table Scans are occurring on the system. Another disadvantage of fragmentation is that you can get out-of-space errors while the total sum of all free space is much more then you had requested.The only way to resolve fragmentation is drop and recreate the object. In most cases doing an export and import will solve the problem. If you need todefragment your system tablespace, you must rebuild the whole database sinceit is NOT possible to drop the system tablespace.References:Note 1020182.6 SCRIPT to detect tablespace fragmentationNote 1012431.6 Common causes of Fragmentation8. Objects----------8.1 Number of Extents~~~~~~~~~~~~~~~~~~~~~~While the performance hit on over extended objects is not significant, theaggregate effect on many over extended objects does impact performance. Thefollowing query will list all the objects that have allocated more extentsthan a specified minimum. Change the <--minext--> value by an actual number,in general objects allocating more then 100 a 200 extents can be recreatedwith larger extent sizes:SQL> select owner, segment_type, segment_name, tablespace_name,count(blocks), SUM(bytes/1024) "BYTES K", SUM(blocks)from dba_extentswhere owner NOT IN ('SYS','SYSTEM')group by owner, segment_type, segment_name, tablespace_namehaving count(*) > <--minext-->>order by segment_type, segment_name;8.2 Next extent~~~~~~~~~~~~~~~~It is important that segments can grow and therefore allocate their next extentwhen needed. If there is not enough free space in the tablespace then the nextextent can not be allocated and the object will fail to grow.The following query returns all the segments that are unable to allocate theirnext extent :SQL> select s.owner, s.segment_name, s.segment_type,s.tablespace_name, s.next_extentfrom dba_segments swhere s.next_extent > (select MAX(f.bytes)from dba_free_space fwhere f.tablespace_name = s.tablespace_name);Note that if there is a lot of fragmentation in the tablespace, then this querymay give you objects that still are able to grow. The above query is based onthe largest free chunk in the tablespace available. If there are a lot of'small' free chunks after each other, then Oracle will coalesce these to servethe extent allocation.Therefore it can be interesting to adapt the script in Note 1020182.6 'SCRIPTto detect tablespace fragmentation' to compare the next extent for each objectwith the 'contiguous' bytes (table space_temp) in the tablespace.8.3 Indexes~~~~~~~~~~~~An index needs to be maintained, every delete or insert on a table resultindirectly on a delete or insert on the underlying index. Over time an indexstructure can get fragmented and therefore the index should be rebuilt.9. AUTO vs MANUAL undo-----------------------Starting from Oracle 9i we introduced a new way of managing the before-images. Previously this was achieved through the RollBack Segments or also referred to as manual undo. Automatic undo is used when the UNDO_MANAGEMENT parameter is set to AUTO. When not set or set to MANUAL then we use the 'old' rollback segment mechanism. Although both versions are still available in current release, automatic undo is preferred.9.1 AUTO UNDO~~~~~~~~~~~~~~~There is little to no configuration involved to AUM (Automatic Undo Management). You basically define the amount of time the before image needs to be kept available.This is controlled through the parameter UNDO_RETENTION, defined in seconds. So a value of 900 indicates 15 minutes.It is important to realize that this value is not honored when we are under space pressure in the undo tablespace.Therefore the following formula can be used to calculate the optimal undo tablespace size:Note 262066.1: How To Size UNDO Tablespace For Automatic Undo ManagementStarting from Oracle 10g, you may choose to use the GUARANTEE option, to make sure the undo information does not get overwritten before the defined undo_retention time.Note 311615.1: Oracle 10G new feature - Automatic Undo Retention Tuning9.2 MANUAL UNDO~~~~~~~~~~~~~~~~~~o Damaged rollback segments will prevent the instance to open the database. Only if names of rollback segments are known, corrective action can be taken. Therefore specify all the rollback segments in the 'rollback_segments' parameter in theinit.orao Too small or not enough rollback segments can have serious impact on the behavior of your database. Therefore several issues must be taken into account. Thefollowing query will show you if there are not enough rollback segments onlineor if the rollback segments are too small.SQL> select d.segment_name, d.tablespace_name, s.waits, s.shrinks,s.wraps, s.statusfrom v$rollstat s, dba_rollback_segs dwhere n = d.segment_idorder by 1;SEGMENT_NAME TABLESPACE_NAME WAITS SHRINKS WRAPS STATUS---------------- ----------------------- --------- --------- --------- --------RB1 ROLLBACK_DATA 1 0 160 ONLINERB2 ROLLBACK_DATA 31 1 149 ONLINESYSTEM SYSTEM 0 0 0 ONLINEThe WAITS indicates which rollback segment headers had waits for them. Typically you would want to reduce such contention by adding rollback segments.If SHRINKS is non zero then the OPTIMAL parameter is set for that particularrollback segment, or a DBA explicitly issued a shrink on the rollback segment.The number of shrinks indicates the number of times a rollback segment shrinkedbecause a transaction has extended it beyond the OPTIMAL size. If this value is too high then the value of the OPTIMAL size should be increased as well as theoverall size of the rollback segment (the value of minextents can be increasedor the extent size itself, this depends mostly on the indications of the WRAPScolumn).The WRAPS column indicate the number of times the rollback segment wrapped toanother extent to serve the transaction. If this number is significant then you need to increase the extent size of the rollback segment.Reference:Note 62005.1 Creating, Optimizing, and Understanding Rollback Segments10. Memory Management---------------------This chapter is very version driven. Depending on which version you are running the option available will be different. Overtime Oracle has invested a great deal of time and effort in managing the memory more efficiently and transparently for the end-user.Therefore it is advisable to use the automation features as much as possible.10.1 Pre Oracle 9i~~~~~~~~~~~~~~~~~~~The different memory components (SGA & PGA) needed to be defined at the startup of thedatabase. These values were static. So if one of the memory components was too low thedatabase needed to be restarted to make the changes effective.How to determine the optimal or best value for the different memory components is not covered in this note, since this would lead us too far. However a parameter that was often misused in these versions is the sort_area_size.The 'sort_area_size' parameter in the init.ora defines the amount of memory that can beused for sorting. This value should be chosen carefully since this is part of the User Global Area (UGA) and therefore is allocated for each user individually.If there are a lot of concurrent users performing large sort operation on the databasethen the system can run out of memory.E.g.: You have a sort_area_size of 1Mb, with 200 concurrent users on the database. Although this memory is allocated dynamically, it can allocate up to 200Mband therefore can cause extensive swapping on the system.10.2 Oracle 9i~~~~~~~~~~~~~~~Starting from Oracle 9i we introduced the parametersworkarea_size_policy = [AUTO | MANUAL]pga_aggregate_target = <value>This allows you define 1 pool for the PGA memory, which will be shared across sessions. When you often receive ORA-4030 errors, then this can be an indication that this valueisspecified too low.10.3 Oracle 10g~~~~~~~~~~~~~~~~Automatic Shared Memory Management (ASMM) was introduced in 10g. The automatic shared memorymanagement feature is enabled by setting the SGA_TARGET parameter to a non-zero value.This feature has the advantage that you can share memory resources among the different components.Resources will be allocated and deallocated as needed by Oracle automatically.Automatic PGA Memory management is still available through the 'workarea_size_policy' and'pga_aggregate_target' parameters.10.4 Oracle 11g~~~~~~~~~~~~~~~~Automatic Memory Management (AMM) is being introduced in 11g. This enables automatic tuningof PGA and SGA with use of two new parameters named MEMORY_MAX_TARGET and MEMORY_TARGET.Reference:Note 443746.1: Automatic Memory Management(AMM) on 11g11. Logging & Tracing---------------------11.1 Alert File~~~~~~~~~~~~~~~~The alert log file of the database is written chronologically. Data is always appended and therefore this file can grow to an enormous size. It should becleared or truncated on a regular basis, as a large alert file occupiesunnecessary disk space and can slow down OS write performance to the file.SVRMGR> connect internal/<password>SVRMGR> show parameter background_dump_destNAME TYPE VALUE------------------------------ ------- ----------------------------------background_dump_dest string D:\Oradata\Admin\PROD\Trace\BDumpNote: starting from Oracle 11g, this location is controlled by the 'diagnostic_dest' parameter11.2 Max_dump_file_size~~~~~~~~~~~~~~~~~~~~~~~~Oracle Server processes generate trace files for certain errors or conflicts.These trace files are of use for further analyzing the probleThe init.oraparameter 'max_dump_file_size' limits the size of these trace files. The value of this parameter should be specified in Operating System blocks.Make sure the disk space can handle the maximum size specified, if not thenthis value should be changed.SVRMGR> connect internal/<password>SVRMGR> show parameter max_dump_file_sizeNAME TYPE VALUE----------------------------------- ------- ---------------------max_dump_file_size integer 1024011.3 User and core dump size parameters~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~The parameters 'user_dump_size' and 'core_dump_size' can contain a lot of trace information.It is important to clear this directory at regular times as this can take up a significantamount of space.Note: starting from Oracle 11g, this location is controlled by the 'diagnostic_dest' parameter11.4 Audit files~~~~~~~~~~~~~~~~~By default, every connection as SYS or SYSDBA is logged in an operating system file. The location is controlled through the parameter 'audit_file_dest'. If this parameter isnot set then the location defaults to $ORACLE_HOME/rdbms/audit.Overtime this directory may contain a lot of auditing information and can take up a significant amount of space.11.5 Sqlnet~~~~~~~~~~~~By default sqlnet tracing is disabled while logging for sqlnet connections andthe listener is enabled. These log files are written chronologically and data is always appended. This causes some log files to grow to enormous sizes. Theselarge log files should be cleared or truncated on a regular basis.Activate tracing in case there is a problem that needs to be analyzed. Unnecessary tracing will slow down the system and occupy free disk space. Therefore youshould disable sqlnet and listener tracing when it is not required.To find the location of the logfiles or to activate tracing see:Note 219968.1: SQL*Net, Net8, Oracle Net Services - Tracing and Logging at a Glance <<E--End--。
