If you are new to the AWR reports, the first thing you should probably do is run the ADDM report for the specific time period. The ADDM report provides root cause analysis of the parts of the system consuming the most time. It is often quicker to start with the ADDM report to help narrow down your area of focus in the AWR report.
When looking at an AWR report, a good place to start is the "Top 5 Timed Foreground Events" section, near the top of the report. This gives you an indication of the bottlenecks in the system during this sample period.
Once you've identified the top events, drill down to see what SQL and PL/SQL are consuming the majority of those resources. On the "Main Report" section, click the "SQL Statistics" link.
On the "SQL Statistics" section, click the "SQL ordered by ??" link that most closely relates to the wait event you identified in the "Top 5 Timed Foreground Events" section. In this case, the "DB CPU" was the top event, so it would seem sensible to try the "SQL ordered by CPU Time" link first.
You are then presented with the SQL and PL/SQL that are using most of the specified resource during the sample period. You can then attempt to tune these areas to reduce the impact.
AWR(Automatic Workload Repository) & It's 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$SESS_TIME_MODELandV$SYS_TIME_MODELviews. - Active Session History (ASH) statistics from the
V$ACTIVE_SESSION_HISTORYview. - Some system and session statistics from the
V$SYSSTATandV$SESSTATviews. - Object usage statistics.
- Resource intensive SQL statements.
How to read AWR report?
This section contains detailed guidance for evaluating each section of an AWR report.
Report Summary: This gives an overall summary of the instance during the snapshot period, and it contains important aggregate summary information.
Cache Sizes (end): This shows the size of each SGA region after AMM has changed them. This information can be compared to the original init.oraparameters at the end of the AWR report.
Load Profile: This important section shows important rates expressed in units of per second and transactions per second.
Instance Efficiency Percentages: With a target of 100%, these are high-level ratios for activity in the SGA.
Shared Pool Statistics: This is a good summary of changes to the shared pool during the snapshot period.
Top 5 Timed Events: This is the most important section in the AWR report. It shows the top wait events and can quickly show the overall database bottleneck.
Wait Events Statistics Section: This section shows a breakdown of the main wait events in the database including foreground and background database wait events as well as time model, operating system, service, and wait classes statistics.
Wait Events: This AWR report section provides more detailed wait event information for foreground user processes which includes Top 5 wait events and many other wait events that occurred during the snapshot interval.
Background Wait Events: This section is relevant to the background process wait events.
Time Model Statistics: Time mode statistics report how database-processing time is spent. This section contains detailed timing information on particular components participating in database processing.
Operating System Statistics: The stress on the Oracle server is important, and this section shows the main external resources including I/O, CPU, memory, and network usage.
Service Statistics: The service statistics section gives information about how particular services configured in the database are operating.
SQL Section: This section displays top SQL, ordered by important SQL execution metrics.
SQL Ordered by Elapsed Time: Includes SQL statements that took significant execution time during processing.
SQL Ordered by CPU Time: Includes SQL statements that consumed significant CPU time during its processing.
SQL Ordered by Gets: These SQLs performed a high number of logical reads while retrieving data.
SQL Ordered by Reads: These SQLs performed a high number of physical disk reads while retrieving data.
SQL Ordered by Parse Calls: These SQLs experienced a high number of reparsing operations.
SQL Ordered by Sharable Memory: Includes SQL statements cursors which consumed a large amount of SGA shared pool memory.
SQL Ordered by Version Count: These SQLs have a large number of versions in shared pool for some reason.
Instance Activity Stats: This section contains statistical information describing how the database operated during the snapshot period.
Instance Activity Stats (Absolute Values): This section contains statistics that have absolute values not derived from end and start snapshots.
Instance Activity Stats (Thread Activity): This report section reports a log switch activity statistic.
I/O Section: This section shows the all important I/O activity for the instance and shows I/O activity by tablespace, data file, and includes buffer pool statistics.
Tablespace IO Stats
File IO Stats
Buffer Pool Statistics
Advisory Section: This section show details of the advisories for the buffer, shared pool, PGA and Java pool.
Buffer Pool Advisory
PGA Aggr Summary: PGA Aggr Target Stats; PGA Aggr Target Histogram; and PGA Memory Advisory.
Shared Pool Advisory
Java Pool Advisory
Buffer Wait Statistics: This important section shows buffer cache waits statistics.
Enqueue Activity: This important section shows how enqueue operates in the database. Enqueues are special internal structures which provide concurrent access to various database resources.
Undo Segment Summary: This section gives a summary about how undo segments are used by the database.
Undo Segment Stats: This section shows detailed history information about undo segment activity.
Latch Activity: This section shows details about latch statistics. Latches are a lightweight serialization mechanism that is used to single-thread access to internal Oracle structures.
Latch Sleep Breakdown
Latch Miss Sources
Parent Latch Statistics
Child Latch Statistics
Segment Section: This report section provides details about hot segments using the following criteria:
Segments by Logical Reads: Includes top segments which experienced high number of logical reads.
Segments by Physical Reads: Includes top segments which experienced high number of disk physical reads.
Segments by Buffer Busy Waits: These segments have the largest number of buffer waits caused by their data blocks.
Segments by Row Lock Waits: Includes segments that had a large number of row locks on their data.
Segments by ITL Waits: Includes segments that had a large contention for Interested Transaction List (ITL). The contention for ITL can be reduced by increasing INITRANS storage parameter of the table.
Dictionary Cache Stats: This section exposes details about how the data dictionary cache is operating.
Library Cache Activity: Includes library cache statistics describing how shared library objects are managed by Oracle.
SGA Memory Summary: This section provides summary information about various SGA regions.
init.ora Parameters: This section shows the original init.ora parameters for the instance during the snapshot period.
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