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- About the Statistics tab
- How the Statistics tab is structured
- About the entities you can examine
- How the Statistics tab can help you identify performance problems
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The Statistics tab is primarily intended for instance tuning. You can also use the tab to periodically monitor the health of your instance. It lets you provide answers to the following types of questions: Is Oracle using resources efficiently? Is the SGA correctly sized? Do our systems have enough memory to enable us to keep adding dedicated server processes? Are we performing too many logical I/Os?.
With each release of the database, Oracle introduces new statistics. For example, operating system-related statistics were introduced in Oracle 10g. Precise for Oracle displays this information when available.
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If you want detailed information on a wait event, in the Association area, click the row of the event that you want to view detailed information for. The Tab heading indicates the newly selected entity, and the Main area displays over time graphs for the wait event you drilled down to. There is no Association Area data for a wait event. See “How How most tabs are structured” on page 22structured.
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The following graphs are displayed:
Table 10- 1 Graphs of the RAC Database Cache view
| Graph | Description |
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| GC Blocks Transfer | It displays the total aggregated number of global cache current blocks and global cache CR blocks that have been transferred. |
| Avg. GC Blocks Access Latency (Msec.) | It displays the following average end-to-end elapsed time, or latency for a global cache block request:
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| CR Blocks Request Latency (Avg.) | It displays the following breakdown of the average end-to-end elapsed time, or latency for a CR block request:
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| Current Blocks Request Latency (Avg.) | It displays the following breakdown of the average end-to-end elapsed time, or latency for a current block request:
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About information on instances in the RAC database
The Instance in Database view, in the Statistics tab, displays the following additional RAC database information:
Table 10- 2 Additional RAC database information
| Information | Description |
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| Database | Displays the logical name of the RAC database. |
| DB Name | Displays the Oracle database ID for the instance. |
| DB ID | Displays the Oracle database ID. |
| Instance Number | Displays the number of the instance in the RAC database. |
| Instances | Displays the number of instances that share the same RAC database with the selected instance. |
| Instance Sessions | Number of current instance sessions in the database. |
| Database Sessions | Number of total database sessions. |
| Time Non-Idle Wait Event | Pie chart comparing the amount of non-idle wait time experienced by the selected instance vs. the entire database. |
| Latches | Pie chart comparing the amount of latch wait time experienced by the selected instance vs. the entire database. |
| Logical I/O | Pie chart comparing the amount of logical I/O experienced by the selected instance vs. the entire database. |
| Statement Executions | Pie chart comparing the number of statements executed by the selected instance vs. the entire database. |
About the load of a Tier, instance, or database
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- Buffer Cache Hit Ratios. It displays the buffer cache hit ratio, expressed as a percentage, for each of the buffer pools. From Oracle 9i onwards, different tablespaces may be defined with different block sizes. Each block size has its own buffer pool.
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- Waits on Buffer Cache
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- . It displays the number of waits on all pools, divided into the number of buffer busy waits and free buffer waits.
About parsing information for a Tier, instance, or database
The Parsing view, in the Statistics tab, displays bar graphs for the selected time period. The Parsing view displays the following bar graphs:■ Hard
- Hard Parse Ratio
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- . It displays the percentage of statements that required a hard parse as a proportion of total parses. A high figure may indicate that Oracle is unable to share statements in the shared pool, for example, if the application uses literals instead of bind variables.
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- Soft Parses
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- . It displays the number of statements requiring a soft parse.
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- Library Cache Hit Ratio
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- . It displays the percentage of statements that were already in the shared pool when Oracle began parsing them. A low figure may indicate that the shared pool is too small, or that the applications are not using bind variables or cursor sharing.
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- Parse Times (Sum.) - Oracle 10g
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- . It displays the total duration of all parse times for Oracle 10g. This information is taken from
V$SYS_TIME_MODEL.
About sorting information for a Tier, instance, or database
The Sorting view, in the Statistics tab, displays bar graphs for the selected time period. The Sorting view displays the following bar graphs:■ Disk
- Disk Sorts
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- . It displays the number of sorts that required a write to disk and could not be done entirely in memory.
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- Disk Sorts Ratio
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- . It displays the percentage of sorts requiring a write to disk compared with the total number of sort operations
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- (in-memory and to disk). It is much faster to perform sorts entirely in memory if possible and so a high ratio may indicate a performance problem.
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- Rows Sorted
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- . It displays the total number of rows sorted.
About the redo activity of a Tier, instance, or database
The Redo Activity view, in the Statistics tab, displays bar graphs for the selected time period. The Redo Activity view displays the following bar graphs:■ Generated
- Generated Redo Log
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- . It displays total amount of redo log data generated.
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- Redo Wait Time
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- . It displays the amount of time that applications waited on Redo Log Buffer wait, Log Switch, and Clear wait. Note that these are Precise for Oracle wait categories—the underlying Oracle waits are log file sync, log file switch completion, and so on.
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- Redo Writes
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- . It displays the total number of writes to the redo log buffer.
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- Commits and Rollbacks
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- . It displays the total number of transactions committed or rolled back.
About the checkpoints of a Tier, instance, or database
The Checkpoints view, in the Statistics tab, displays bar graphs for the selected time period. The Checkpoints view displays the following bar graphs:■ Background
- Background Checkpoints. It displays the total number of checkpoints completed or interrupted.
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- Physical Writes. It displays the total number of checkpoint physical writes and other physical writes to disk. This parameter provides an understanding of the checkpoint contribution to total write activity.
About SQL*Net information for a Tier, instance, or database
The SQL*Net view, in the Statistics tab, displays bar graphs for the selected time period. The SQL*Net view displays the following bar graphs:■ SQL
- SQL*Net Client Throughput. It displays the amount of data sent from the Oracle server process to the client process.
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- SQL*Net Client Roundtrips. It displays the total number of client requests. This is mainly the number of times a cursor is opened and executed, and the number of fetches required to retrieve all the data.
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- SQL*Net DB Link Throughput. It displays the amount of data sent from the Oracle server process to a remote Oracle server process using a database link.
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- SQL*Net DB Link Roundtrips. It displays the total number of messages sent/received from the Oracle server process to a remote Oracle server process using a database link.
If these figures are unusually high, it may be an indication that queries are returning more data than necessary, rather than the minimum set of rows and columns. Another possibility is that the application may be inefficient in terms of networking; you may want to examine the SQL*NET parameters, such as the Session Data Unit (SDU) size.
About latching information for a Tier, instance, or database
The Latching view, in the Statistics tab, displays bar graphs for the selected time period. The Latching view displays the following bar graphs:■ Wait
- Wait Times (Sum.). It displays the total amount of time that Oracle has spent waiting for a latch to become available. The time is broken down into various categories according to latch type. To see the full list of latches and their categorization, click Latches from the Association controls in the Association Area. Note that this categorization is defined within Precise for Oracle.
About operating system information for a Tier, instance, or database
The Operating System (Oracle 10g and Later) view, in the Statistics tab, displays bar graphs for the selected time period.
The Operating System view displays the following bar graphs:■ CPU
- CPU Utilization. It displays the percentage of all the available CPUs on the server used by Oracle, broken down into system time and user time.
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- Paging. It displays the average number of bytes paged-in and paged-out per second by Oracle.
About system time model information for a Tier, instance, or database
The System Time Model (Oracle 10g and Later) view, in the Statistics tab, displays graphs for the selected time period. The System Time Model view displays the following graphs:■ Oracle
- Oracle (DB and Background) Time. It displays Oracle time broken down into DB CPU time, elapsed CPU background time, and elapsed non-CPU background time.
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- DB Elapsed Time. It displays database time only, broken down into sequence load elapsed time, parse time, SQL execute time, connection management time, PL/SQL execution time, PL/SQL compilation time, inbound PL/SQL RPC time and Java execution time.
About the Wait Event entity
The Wait Event entity, in the Statistics tab, displays Oracle wait event information that is derived from the V$SYSTEM_EVENT table.
Examining a wait event over time
The Over Time view, in the Statistics tab, displays graphs for the selected time period. The Over Time view displays the following graphs:■ Event
- Event Waits vs. Timeouts. It displays the total number of occurrences of the wait event vs. the number that exceeded the timeout.
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- Times Waited (Sum.). It displays the total time waited.
You cannot associate a wait event with any other entity.
About information on wait events
When you view information on wait events in the Association area of the Statistics tab, the information is displayed in a table.
The following table shows Wait event information in the Association area.
Table 10- 3 Wait event information in the Association areaColumn Description
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| Wait |
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| Event | Name of the Oracle wait event. |
| In Oracle Sub- |
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| State | Equivalent Precise for Oracle wait sub-state. See |
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| Wait States. | |
| Idle | Indicates whether Precise for Oracle categorizes the wait event as an idle event. Precise for Oracle considers certain events, such as sql*net message from client, rdbms ipc message or pmon timer, as idle because Oracle is effectively sleeping and not consuming any resources. The categorization affects the top 10 wait events displayed in the Wait Event view of the Tier or an instance. |
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| Waits | Total number of occurrences of the wait event. |
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| Timeouts | Total number of occurrences of the wait event that exceeded the timeout. Some events have a timeout associated with them. |
| Times Waited (Sum.) |
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| Total time waited, displayed as a duration and bar graph. |
About the Block Contentions entity
The Block Contention entity, in the Statistics tab, displays information that is derived from the V$WAITSTAT table.
About a block contention over time
The Over Time view, in the Statistics tab, displays a graph for the selected time period. The Over Time view displays the following graph:■ Block
- Block Contention Waits vs. Time Waited
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- . It displays the total number of block contentions vs. the total time waited. You cannot associate a block contention with any other entity.
About information on block contentions
When you view information on block contentions in the Association area, the following information is displayed in the table:
Table 10- 4 Block contention information in the Association areaColumn Description
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| Block Contention | Name of the block contention. |
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| Waits | Total number of block contention waits. |
| Times Waited (Sum.) |
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| Total time waited, displayed as a duration and bar graph. |
About the Latch entity
The Latch entity, in the Statistics tab, displays information that is derived from the V$LATCH table.
About a latch over time
The Over Time view, in the Statistics tab, displays graphs for the selected time period. The Over Time view displays the following graphs:■ Wait
- Wait Times (Sum.). It displays the total time Oracle spent waiting for the latch to become available.
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- Latch Miss Ratio. It displays the number of requests to get a latch which were unsuccessful. It includes Willing to Wait Miss Ratio and No Wait Miss Ratio.
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- Latch Misses. It displays the total number of latch misses. It includes the number of Willing to Wait Misses and No Wait Misses. You cannot associate a latch with any other entity.
About information on latches
When you view information on latches in the Association area, the following information is displayed in the table:
Table 10- 5 Latch information in the Association area
Column Description
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| Column | Description |
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| Latch | Name of the latch. |
| Class |
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| Precise for Oracle categorization of the latch. Precise for Oracle uses these categories to display a breakdown of latch types in the Latching view of a Tier or instance. |
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| Misses | Bar graph showing the number of Willing to Wait misses and No Wait misses. Willing to Wait misses is equivalent to MISSES in V$LATCH; No Wait misses is equivalent to IMMEDIATE_MISSES in V$LATCH. |
| Willing to Wait Miss |
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| Radio | Percentage of requests to get a latch that were unsuccessful but the caller was willing to wait. Equivalent to the ratio of MISSES to GETS in V$LATCH. |
| No Wait Miss |
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| Radio | Percentage of requests to get a latch that were unsuccessful but the caller was not willing to wait. Equivalent to the ratio of IMMEDIATE_MISSES to IMMEDIATE_GETS in V$LATCH. |
| Wait Times (Sum.) |
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| Total time Oracle spent sleeping, waiting on the latch to become available, displayed as a duration and bar graph. |
About the Statistics entity
The Statistics entity, in the Statistics tab, displays information that is derived from the V$SYSSTAT table.
About statistics over time
The Over Time view, in the Statistics tab, displays a bar graph for the selected time period. The Over Time view displays the following bar graph:
■ Statistics
- Statistics. Displays the value of the statistic.
You cannot associate statistics with any other entity.
About statistics information
When you view statistics information in the Association area, the following information is displayed in the table:
Table 10- 6 Statistics information in the Association area
Column Description
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| Column | Description |
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| Statistic | Name of the Oracle statistic. |
| Class |
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| Oracle class of statistic. |
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| Value | Statistic value. |
You can use the More... option in the Association controls to populate the association area with a subset of statistics based on class. For example, you can click Statistics>Cache or Statistics>Debug Statistics > Cache or Statistics > Debug. Some statistics are classified more than once. For example, Buffer is Pinned Count is classified as both Cache and SQL.
About the Database Time Statistics entity
The Database Time Statistics (Oracle 10g and later) entity, in the Statistics tab, displays information that is derived from the V$SYS_TIME_MODEL table.
About database time statistics over time
The Over Time view, in the Statistics tab, displays a graph for the selected time period. The Over Time view displays the following graph:■ Times
- Times Waited (Sum.)
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- . Displays the total time waited.
You cannot associate database time statistics with any other entity.
About database time statistics information
When you view database time statistics information in the Association area, the following information is displayed in the table:
Table 10- 7 Database time statistics information in the Association area
Column Description
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| Column | Description |
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| Statistic | Name of the statistic. |
| Times Waited (Sum.) |
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| Total time waited, displayed as a duration and bar graph. |
About the Operating System Statistics entity
The Operating System Statistics (Oracle 10g and later) entity, in the Statistics tab, displays information that is derived from the V$OSSTAT table.
About operating system statistics
The Overview, in the Statistics tab, displays processor-related and paging-related statistics for the selected time period.Note:
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Precise for Oracle only provides operating system statistics as reported by Oracle; some operating systems may not necessarily report accurate statistics, and Oracle may provide different statistics depending on the specific operating system. |
You cannot associate operating system statistics with any other entity.
When you view database time statistics information in the Association area, the following information is displayed in the table:
Table 10- 8 Operating system statistics information in the Association area
Column Description
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| Column | Description |
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| Statistic | Name of the statistic. |
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| Type | Type of statistic. Values are Processor or Paging |
| Processor |
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| Time | Amount of CPU time consumed. This and the Utilization column are only available for |
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| Processor-related statistics. |
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| Utilization | CPU utilization. |
| Paged |
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| Bytes | Total number of bytes paged in or out. This and the Paged Bytes/sec column are only available for |
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| Paging-related statistics. |
| Paged Bytes/Sec. |
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| Average number of bytes paged in or out per second. | |
| Description |
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| Provides a description of the statistic. |
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To determine whether Oracle is performing optimally, it is necessary to monitor the health of your instances, and at times to tune your instances. The Statistics tab provides many performance counters grouped into several predefined graphs that display related counters that enable you to locate performance problems in your system.
You can identify a performance problem by doing one or more of the following:■ Examining
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We should begin our analysis with the Instance overview. This view displays the Top 10 Wait Events in a pie chart.Note:
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The pie chart will not display what are considered to be idle events. |
See Examining latches.
“Examining latches” on page 176. To examine top 10 wait events1 In
- In the Time Frame list, choose the period of time you want to analyze.
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- In the Instance list, choose the item you want to analyze.
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- In the Association area, click Wait Events to observe the wait events that are associated with the selected instance and their wait duration.
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After we have examined the top 10 wait events, we now need to determine which latch or latches are contributing to the latch free event.
To examine latches1 In , in the Association area, click Latches from the Association controls. The Statistics tab displays the latches that are associated with this instance.
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One of the recommended ways to tune statements is to reduce the number of logical I/Os, because logical I/Os tend to dominate response time. It is important to understand how the number of logical I/Os varies over time. The instance statistics in the Statistics tab re-enforce the resource consumption figures observed in the Activity tab.
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We can tune statements by examining the current number of consistent gets for a period of time.
To examine consistent gets1 In
- In the Time Frame list, choose the period of time you want to analyze.
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- Open the statement you want to analyze in the Statistics tab. For our example, the Statistics tab shows the logical I/O for All Oracle Instances. We can see that the number of logical I/Os remained fairly constant on the evening of September 22nd. The logical I/Os are nearly all made up of Consistent Gets (that is, fetching read-consistent copies of data).
In the Association area, you see that the logical I/O count is dominated by ora920 on linuxi4o2. This is the instance we should look at when considering tuning of logical I/Os. Observe the number of logical/Os per execution. Notice the upward trend. This, together with the total number of logical I/Os, indicates that fewer statements are being run, but each statement is processing more data. This may indicate that the application is I/O bound because it cannot handle more than a certain number of I/Os.
Examining DB block gets
We can also tune statements by examining the number of DB block gets.
To examine DB block gets1 In
- In the Time Frame list, choose the period of time you want to analyze.
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- Open the statement you want to analyze in the Statistics tab. In our example, we observe two major peaks in I/O activity, one on the 13th of September and one on the 17th. For our example, the Logical I/O Operations graph shows an increase on the 17th and that the logical I/O was split fairly evenly. The logical I/O was split between DB Block Gets, which are fetching the current version of the data, and DB Block Changes, which are updating the current version of the data. This indicates that there was heavy DML activity on these two days.
The Logical I/O Operations per Execution graph shows that the number of logical I/O operations per execution remained roughly constant on these two days. Together, both graphs will imply that approximately twice as many statements were executed on the 17th.
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It is usually good practice to examine logical I/Os first because it is a more reliable measure than physical I/Os, due to caching effects that can complicate an analysis of physical I/Os.
To examine physical I/Os1 First
- First examine logical I/Os. See
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- Now examine physical I/Os. For our example, the Statistics tab shows sampled data from the same time period as that shown for consistent gets over time. We can see that the average read and write time follows the number of physical I/O operations reasonably close, particularly the first peak on September 22nd. This indicates that there is some contention between I/O operations, perhaps because they are all reading from different points on the same disk, causing a rise in seek time.
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If you are looking to reduce the amount of memory used by Oracle, or looking to increase one of the memory buffers without increasing the overall memory footprint, you can use the memory view.
To examine memory1 In
- In the Time Frame list, choose the period of time you want to analyze.
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- Open the statement you want to analyze in the Statistics tab. For our example, the Statistics tab shows data that was gathered over a 16-day period. All 32MB of the Java pool is free; all 8 MB of the large pool is free, and at least
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- 15 MB of the shared pool is free.
The Association area lists all Oracle events that are in the Shared Pool Wait category. As would be expected (for a shared pool that is not full), there has been very little wait time.
For this example, the Aggregated PGA Target has been set to 24 MB and a maximum of 19 MB has been used. This leaves us with very little scope by which to reduce total PGA memory.
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Oracle 10g provides even more statistics than were provided by previous versions. Precise for Oracle displays graphs of some of the more important statistics, such as CPU utilization and parse times.
To examine parse times1 In
- In the Time Frame list, choose the period of time you want to analyze.
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- Open the statement you want to analyze in the Statistics tab.
For our example, we will examine how a number of hard parses affects the parse time. If we look at the Hard Parse Ratio graph in the Main area, we can observe that the hard parse ratio increased to around 50% at 6 PM, meaning that some new statements were executed or required reloading. Consequently, the total parse time increased to around 15 minutes. Then the number of statements that required parsing remained fairly constant (shown on the Soft Parse graph), but the hard parses fell away and so did the parse times. This example explains why it is a good idea to use bind variables or cursor sharing.
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