What is AWR( Automatic workload repository ) and How to generate the AWR report
- (AWR) Automatic workload repository is a collection of persistent system performance statistics owned by SYS. It resides in SYSAUX tablespace.
- By default snapshot are generated once every 60 min and maintained for 7 days.
- Each snapshot has a unique ID know as "snap_id". Snapshot detail can be found in "dba_hist_snapshot" view.
So before generating the AWR
Report let's find time interval for which we need AWR Report.
Suppose we need AWR Report for 05-MAY-17. To achieve this we need snapshot ID for this data.
How to find Snap Id:
Suppose we need AWR Report for 05-MAY-17. To achieve this we need snapshot ID for this data.
How to find Snap Id:
Select from dba_hist_snapshot view
which have two fields "BEGIN_INTERVAL_TIME" and "END_INTERVAL_TIME".
These fields give exact value for time this snap shot belongs.
From above table select your snap_id in the meantime for 05-MAY-17. In this case starting snap_id is 2676 and it goes up to 2699.
For more detail about dba_hist_snapshot Please visit:
From above table select your snap_id in the meantime for 05-MAY-17. In this case starting snap_id is 2676 and it goes up to 2699.
For more detail about dba_hist_snapshot Please visit:
- Steps to Generate AWR Report:
1. Log in to database:
[oracle@test ~]$ export ORACLE_SID=test01
[oracle@test ~]$ sqlplus sys as sysdba
2. Execute command for Report generation:
[oracle@test ~]$ export ORACLE_SID=test01
[oracle@test ~]$ sqlplus sys as sysdba
2. Execute command for Report generation:
SQL> @ $ORACLE_HOME/rdbms/admin/awrrpt.sql
3. Choose Report Type:
It will prompt
for AWR report type. This report can be generated in two types "HTML"
and "TEXT". Default is HTML
Specify the Report
Type
~~~~~~~~~~~~~~~~~~~~~~~
Would you like an HTML report, or a plain text report?
Enter 'html' for an HTML report, or 'text' for plain text
Defaults to 'html'
Enter value for report_type: HTML
~~~~~~~~~~~~~~~~~~~~~~~
Would you like an HTML report, or a plain text report?
Enter 'html' for an HTML report, or 'text' for plain text
Defaults to 'html'
Enter value for report_type: HTML
4. Snap details: You can give any value it
will show you all snap id's and detail for given no of days.
Enter value for num_days: 2
Enter value for num_days: 2
5. Specify the Begin
and End Snapshot Ids:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enter value for begin_snap:2676
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enter value for begin_snap:2676
Enter value for
end_snap: 2699
Here you need to give
begin and end snap id.
6. Specify Report
Name: Default is
awrrpt_1_begin_span_id_end_snap_id.html. Press enter for default name or give
new name.
Specify the Report
Name
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is awrrpt_1_2676_2699.html. To use this name, press to continue, otherwise enter an alternative.
Enter value for report_name:
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is awrrpt_1_2676_2699.html. To use this name, press to continue, otherwise enter an alternative.
Enter value for report_name:
7. Report
generated: your report is generated at present working
directory.
Report written to awrrpt_1_2676_2699.html
8. To get the
report:
SQL> exit;
[oracle@test]$ pwd
/home/oracle
9. Read AWR Report: Go to /home/oracle find file as "awrrpt_1_2676_2699.html"
This is your AWR
report generated.
10. Steps to Analyze AWR
Report in Oracle
As you have Generated AWR Report in Oracle, Next task is to Analyze AWR
Report in Oracle. By Reading AWR Report you can
easily solve issues like Slow
database, high wait events, Slow query and many more. Though It's a
lengthy report but Analyzing or Reading relevant part of AWR Report can
help to troubleshoot issues in easy and fast manner.
- AWR stands for Automatically workload repository, though there could be many types of database performance issues, but when whole database is slow, then there are two possibilities.
1. Issue with Database Machine. OS Watcher is the best tool to start.
2. If Database performance issue, Then AWR Report is the place to look at.
2. If Database performance issue, Then AWR Report is the place to look at.
- In case if a particular query is not performing well, I would suggest looking at execution plan of the query, stats of underlying table etc. In this case AWR won't help much.
Recommendations before getting an AWR Report.
1. Collect Multiple AWR Reports: It's always good to have two AWR Reports, one for good time (when database was performing well), second when performance is poor. This way Remote DBA can easily compare good and bad report to find out the culprit.
2. Stick to Particular Time: "Database is performing slow" will not help anymore to resolve performance issues. We must have a specific time like Database was slow yesterday at 1 Pm and continue till 4Pm. Here, DBA will get a report for these three hours.
3. Split Large AWR Report into Smaller Reports: Instead of having one report for long time like one report for 4hrs. it's is better to have four reports each for one hour. This will help to isolate the problem.
In case of RAC env. generate one report for each instance. Once, you have generated AWR report. Now, it's time of analyze the report. Since, AWR report is a huge report and area to consider AWR is also depends on problem to problem. Here, I list most common area for a DBA to look into which will give a clear picture of the issue.
1. Collect Multiple AWR Reports: It's always good to have two AWR Reports, one for good time (when database was performing well), second when performance is poor. This way Remote DBA can easily compare good and bad report to find out the culprit.
2. Stick to Particular Time: "Database is performing slow" will not help anymore to resolve performance issues. We must have a specific time like Database was slow yesterday at 1 Pm and continue till 4Pm. Here, DBA will get a report for these three hours.
3. Split Large AWR Report into Smaller Reports: Instead of having one report for long time like one report for 4hrs. it's is better to have four reports each for one hour. This will help to isolate the problem.
In case of RAC env. generate one report for each instance. Once, you have generated AWR report. Now, it's time of analyze the report. Since, AWR report is a huge report and area to consider AWR is also depends on problem to problem. Here, I list most common area for a DBA to look into which will give a clear picture of the issue.
- Steps to Analyze AWR Report
1. Database Details:
After getting an AWR Report This is first and Top part of the report. In this part cross check for database and instance and and database version with the Database having performance issue. This report also show RAC=YES if it's an RAC database.
After getting an AWR Report This is first and Top part of the report. In this part cross check for database and instance and and database version with the Database having performance issue. This report also show RAC=YES if it's an RAC database.
2. Host Configuration:
This will give you name, platform, CPU, socket and RAM etc. Important thing to notice is number of cores into the system. In this example there are 12 CPU's in Cores.
This will give you name, platform, CPU, socket and RAM etc. Important thing to notice is number of cores into the system. In this example there are 12 CPU's in Cores.
3. Snap Shot Detail:
This are the detail about snap shot taken, Snap start time and end time. Difference between them is as "Elapsed". Here is a new term "DB Time"
DB Time= session time spent in database.
DB Time= CPU Time + Non-IDLE wait time.
You can find, DB time is very large as compared to Elapse time, which is not a concern. Check if you have taken a report for the time having performance problem. If yes fine, otherwise take a report for performance problem time.
Next is Cache Sizes, which is just detail about SGA components.
4. Load Profile:
Here are few important stats for a DBA to consider. Fist is "DB CPU(s)" per second. Before that let's understand how DB CPU's work. Suppose you have 12 cores into the system. So, per wall clock second you have 12 seconds to work on CPU.
DB Time= CPU Time + Non-IDLE wait time.
You can find, DB time is very large as compared to Elapse time, which is not a concern. Check if you have taken a report for the time having performance problem. If yes fine, otherwise take a report for performance problem time.
Next is Cache Sizes, which is just detail about SGA components.
4. Load Profile:
Here are few important stats for a DBA to consider. Fist is "DB CPU(s)" per second. Before that let's understand how DB CPU's work. Suppose you have 12 cores into the system. So, per wall clock second you have 12 seconds to work on CPU.
So, if "DB CPU(s)" per second in this report > cores in (Host Configuration (#2)).
means env is CPU bound and either need more CPU's or need to further check is this happening all the time or just for a fraction of time. As per my experience there are very few cases, when system is CPU bound.
In this case, machine has 12 cores and DB CPU(s) per second is 6.8. So, this is not a CPU bound case.
Next stat to look at are Parses and Hard parses. If the ratio of hard parse to parse is high, this means Database is performing more hard parse. So, needs to look at parameters like cursor_sharing and application level for bind variables etc.
5. Instance Efficiency Percentages:
In these statistics, you have to look at "% Non-Parse CPU". If this value is near 100% means most of the CPU resources are used into operations other than parsing, which is good for database health.
6. Top 5 Timed Foreground Events:
This is another most important stats to consider while looking at AWR Report for any database performance related issue. This has a list of top 5 foreground wait events.
Here, first of all check for wait class if wait class is User I/O , System I/O, Others etc this could be fine but if wait class has value "Concurrency" then there could be some serious problem. Next to look at is Time (s) which show how many times DB was waiting in this class and then Avg Wait (ms). If Time(s) are high but Avg Wait (ms) is low then you can ignore this. If both are high or Avg Wait (ms) is high then this has to further investigate.
In the above screen shot, most of the resource are taken by DB CPU = 64% DB time. Taking resource by DB CUP is a normal situation.
Let's take an example, In which event is "log file switch (checkpoint incomplete) " which has high waits, huge Time (s) and large values in Avg Wait (ms) and wait class is configuration. So, here you have to investigate and resolve log file switch (checkpoint incomplete).
Host CPU, Instance CPU and Memory Statistics are self explanatory. Next is RAC Statistics, I did not find any issue in these stats most of the time.
7. Time Model Statistics:
This is a detailed explanations of system resource consumptions. Stats are order by Time (s) and % of DB Time.
A noticeable result Sum of all % of DB time is
> 100%. why is this ?
Because this is cumulative time i.e. In this case SQL execute elapsed time is taking 89% of DB time, which includes it sub parts like parse time elapsed, hard parse elapsed time etc. So, if you find Hard parse time elapsed is taking more %. So investigate further so on and so forth.
DBA has to look for stat which is taking abnormal % of DB time.
8. Operating System Statistics - Detail:
This is the information related to OS, what is the load status on System shown here.
Because this is cumulative time i.e. In this case SQL execute elapsed time is taking 89% of DB time, which includes it sub parts like parse time elapsed, hard parse elapsed time etc. So, if you find Hard parse time elapsed is taking more %. So investigate further so on and so forth.
DBA has to look for stat which is taking abnormal % of DB time.
8. Operating System Statistics - Detail:
This is the information related to OS, what is the load status on System shown here.
This report shows, system is 62 and 70% idle at time of report taken, So, there is no resource crunch at system level. But if, you found very high busy, user or sys % and indeed this will led to low idle %. Investigate what is causing this. OS Watcher is the tool which can help in this direction.
Next, very crucial part of AWR report for a DBA is SQL Statistics. Which has all sql query details executed during report time interval.
We will explore few of them, To understand, how to analyzed these reports. Let's start with
9. SQL Ordered by Elapsed Time:
As explained by name itself, this lists SQL queries ordered by Elapsed time into reported time interval.
In this report, look for query has low executions and high Elapsed time per Exec (s) and this query could be a candidate for troubleshooting or optimizations. In above report, you can see first query has maximum Elapsed time but no execution. So you have to investigate this.
In Important point, if executions is 0, it doesn't means query is not executing, this might be the case when query was still executing and you took AWR report. That's why query completion was not covered in Report.
10. SQL Ordered by CPU Time:
In this report, SQL queries are listed on the basis of CPU taken by the query i.e. queries causing high load on the system. The top few queries could be the candidate query for optimization.
From above stat, look for queries using highest CPU Times, If a query shows executions 0, this doesn't means query is not executing. It might be same case as in SQL queries ordered by Elapsed time. The query is still executing and you have taken the snapshot.
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