Carlos Sierra's Tools and Tips

Tools and Tips for Oracle Performance and SQL Tuning

Archive for the ‘AWR’ Category

eDB360 includes now an optional staging repository

with 3 comments

eDB360 has always worked under the premise “no installation required”, and still is the case today – it is part of its fundamental essence: give me a 360-degree view of my Oracle database with no installation whatsoever. With that in mind, this free tool helps sites that have gone to the cloud, as well as those with “on-premises” databases; and in both cases not installing anything certainly expedites diagnostics collections. With eDB360, you simply connect to SQL*Plus with an account that can select from the catalog, execute then a set of scripts behind eDB360 and bingo!, you get to understand what is going on with your database just by navigating the html output. With such functionality, we can remotely diagnose a database, and even elaborate on the full health-check of it. After all, that is how we successfully use it every day!, saving us hundreds of hours of metadata gathering and cross-reference analysis.

Starting with release v1706, eDB360 also supports an optional staging repository of the 26 AWR views listed below. Why? the answer is simple: improved performance! This can be quite significant on large databases with hundreds of active sessions, with frequent snapshots, or with a long history on AWR. We have seen cases where years of data are “stuck” on AWR, specially in older releases of the database. Of course cleaning up the outdated AWR history (and corresponding statistics) is highly recommended, but in the meantime trying to execute edb360 on such databases may lead to long execution hours and frustration, taking sometimes days for what should take only a few hours.

  1. dba_hist_active_sess_history
  2. dba_hist_database_instance
  3. dba_hist_event_histogram
  4. dba_hist_ic_client_stats
  5. dba_hist_ic_device_stats
  6. dba_hist_interconnect_pings
  7. dba_hist_memory_resize_ops
  8. dba_hist_memory_target_advice
  9. dba_hist_osstat
  10. dba_hist_parameter
  11. dba_hist_pgastat
  12. dba_hist_resource_limit
  13. dba_hist_service_name
  14. dba_hist_sga
  15. dba_hist_sgastat
  16. dba_hist_sql_plan
  17. dba_hist_sqlstat
  18. dba_hist_sqltext
  19. dba_hist_sys_time_model
  20. dba_hist_sysmetric_history
  21. dba_hist_sysmetric_summary
  22. dba_hist_sysstat
  23. dba_hist_system_event
  24. dba_hist_tbspc_space_usage
  25. dba_hist_wr_control
  26. dba_hist_snapshot

Thus, if you are contemplating executing eDB360 on a large database, and provided pre-check script edb360-master/sql/awr_ash_pre_check.sql shows that eDB360 might take over 24 hours, then while you clean up your AWR repository you can use the eDB360 staging repository as a workaround to speedup eDB360 execution. The use of this optional staging repository is very simple, just look inside the edb360-master/repo directory for instructions. And as always, shoot me an email or comment here if there were any questions.

Written by Carlos Sierra

February 19, 2017 at 8:43 pm

edb360 taking a long time

with 2 comments

In most cases edb360 takes less than 1hr to execute. But I often hear of cases where it takes a lot longer than that. In a corner case it was taking several days and it had to be killed.

So the question is WHY edb360 takes that long?

Well, edb360 executes thousands of SQL statements sequentially (intentionally). Many of these queries read data from AWR and in particular from ASH. So, lets say your ASH historical table has 2B rows, and on top of that you have not gathered statistics on AWR tables in years, thus CBO under-estimates cardinality and tends to use index access and nested loops. In such extreme cases you may end up with suboptimal execution plans that expect to return a few rows, but actually read a couple of billion rows using index access operations and nested loops. A query like this may take hours to complete!

As of version v1515, edb360 has a shortcut algorithm that ends an execution after 8 hours. So you may get an incomplete output, but it ends normally and the partial output can actually be used. This is not a solution but a workaround for those long executions.

How to troubleshoot edb360 taking long?

Steps:

1. Review files 00002_edb360_dbname_log.txt, 00003_edb360_dbname_log2.txt, 00004_edb360_dbname_log3.txt and 00005_edb360_dbname_tkprof_sort.txt. First log shows the state of the statistics for AWR Tables. If stats are old then gather them fresh with script edb360/sql/gather_stats_wr_sys.sql

2. If number of rows on WRH$_ACTIVE_SESSION_HISTORY as per 00002_edb360_dbname_log.txt is several millions, then you may not be purging data periodically. There are some known bugs and some blog posts on this regard. Review MOS 387914.1 and proceed accordingly. Execute query below to validate ASH age:

SELECT TRUNC(sample_time, 'MM'), COUNT(*)
  FROM dba_hist_active_sess_history
 GROUP BY TRUNC(sample_time, 'MM')
 ORDER BY TRUNC(sample_time, 'MM')
 /

3. If edb360 version (first line on its readme) is older than 1 month, download and use latest version: https://github.com/carlos-sierra/edb360/archive/master.zip (link is also provided on the right-hand side of this blog under downloads).

4. Consider suppressing text and or csv reports. Each for an estimated gain of about 20%. Keep in mind that when suppressing reports, you start loosing some functionality. To suppress lets say text and csv reports, place the following two commands at the end of script edb360/sql/edb360_00_config.sql

DEF edb360_conf_incl_text = ‘N’;
DEF edb360_conf_incl_csv = ‘N’;

5. If after going through steps 1-4 above, edb360 still takes longer than a few hours, feel free to email author carlos.sierra.usa@gmail.com and provide 4 files from step 1.

Written by Carlos Sierra

May 6, 2015 at 8:19 pm

Discovering if a System level Parameter has changed its value (and when it happened)

with 4 comments

Quite often I learn of a system where “nobody changed anything” and suddenly the system is experiencing some strange behavior. Then after diligent investigation it turns out someone changed a little parameter at the System level, but somehow disregarded mentioning it since he/she thought it had no connection to the unexpected behavior.  As we all know, System parameters are big knobs that we don’t change lightly, still we often see “unknown” changes like the one described.

Script below produces a list of changes to System parameter values, indicating when a parameter was changed and from which value into which value. It does not filter out cache re-sizing operations, or resource manager plan changes. Both would be easy to exclude, but I’d rather see those global changes listed as well.

Note: This script below should only be executed if your site has a license for the Oracle Diagnostics pack (or Tuning pack), since it reads from AWR.

WITH
all_parameters AS (
SELECT snap_id,
       dbid,
       instance_number,
       parameter_name,
       value,
       isdefault,
       ismodified,
       lag(value) OVER (PARTITION BY dbid, instance_number, parameter_hash ORDER BY snap_id) prior_value
  FROM dba_hist_parameter
)
SELECT TO_CHAR(s.begin_interval_time, 'YYYY-MM-DD HH24:MI') begin_time,
       TO_CHAR(s.end_interval_time, 'YYYY-MM-DD HH24:MI') end_time,
       p.snap_id,
       p.dbid,
       p.instance_number,
       p.parameter_name,
       p.value,
       p.isdefault,
       p.ismodified,
       p.prior_value
  FROM all_parameters p,
       dba_hist_snapshot s
 WHERE p.value != p.prior_value
   AND s.snap_id = p.snap_id
   AND s.dbid = p.dbid
   AND s.instance_number = p.instance_number
 ORDER BY
       s.begin_interval_time DESC,
       p.dbid,
       p.instance_number,
       p.parameter_name
/

Sample output follows, where we can see a parameter affecting Degree of Parallelism was changed. This is just to illustrate its use. Enjoy this new free script! It is now part of edb360.
Screen Shot 2015-03-25 at 19.15.26

Written by Carlos Sierra

March 25, 2015 at 7:25 pm

Free script to generate a Line Chart on HTML

with 14 comments

Performance Metrics are easier to digest if visualized trough some Line Charts. OEM, eDB360, eAdam and other tools use them. If you already have a SQL Statement that provides the Performance Metrics you care about, and just need to generate a Line Chart for them, you can easily create a CSV file and open it with MS-Excel. But if you want to build an HTML Report out of your SQL, that is a bit harder, unless you use existing technologies. Tools like eDB360 and eAdam use Google Charts as a mechanism to easily generate such Charts. A peer asked me if we could have such functionality stand-alone, and that challenged me to create and share it.

HTML Line Chart
This HTML Line Chart Report above was created with script line_chart.sql shown below. The actual chart, which includes Zoom functionality on HTML can be downloaded from this Dropbox location. Feel free to use this line_chart.sql script as a template to display your Performance Metrics. It can display several series into one Chart (example above shows only one), and by reviewing code below you will find out how easy it is to adjust to your own needs. Chart above was created using a simple query against the Oracle Sample Schema SH, but the actual use could be Performance Metrics or any other Application time series.

Script

SET TERM OFF HEA OFF LIN 32767 NEWP NONE PAGES 0 FEED OFF ECHO OFF VER OFF LONG 32000 LONGC 2000 WRA ON TRIMS ON TRIM ON TI OFF TIMI OFF ARRAY 100 NUM 20 SQLBL ON BLO . RECSEP OFF;
PRO
DEF report_title = "Line Chart Report";
DEF report_abstract_1 = "<br>This line chart is an aggregate per month.";
DEF report_abstract_2 = "<br>It can be by day or any other slice size.";
DEF report_abstract_3 = "";
DEF report_abstract_4 = "";
DEF chart_title = "Amount Sold over 4 years";
DEF xaxis_title = "Sales between 1998-2001";
--DEF vaxis_title = "Amount Sold per Hour";
--DEF vaxis_title = "Amount Sold per Day";
DEF vaxis_title = "Amount Sold per Month";
DEF vaxis_baseline = ", baseline:2200000";
DEF chart_foot_note_1 = "<br>1) Drag to Zoom, and right click to reset Chart.";
DEF chart_foot_note_2 = "<br>2) Some other note.";
DEF chart_foot_note_3 = "";
DEF chart_foot_note_4 = "";
DEF report_foot_note = "This is a sample line chart report.";
PRO
SPO line_chart.html;
PRO <html>
PRO <!-- $Header: line_chart.sql 2014-07-27 carlos.sierra $ -->
PRO <head>
PRO <title>line_chart.html</title>
PRO
PRO <style type="text/css">
PRO body   {font:10pt Arial,Helvetica,Geneva,sans-serif; color:black; background:white;}
PRO h1     {font-size:16pt; font-weight:bold; color:#336699; border-bottom:1px solid #cccc99; margin-top:0pt; margin-bottom:0pt; padding:0px 0px 0px 0px;}
PRO h2     {font-size:14pt; font-weight:bold; color:#336699; margin-top:4pt; margin-bottom:0pt;}
PRO h3     {font-size:12pt; font-weight:bold; color:#336699; margin-top:4pt; margin-bottom:0pt;}
PRO pre    {font:8pt monospace;Monaco,"Courier New",Courier;}
PRO a      {color:#663300;}
PRO table  {font-size:8pt; border_collapse:collapse; empty-cells:show; white-space:nowrap; border:1px solid #cccc99;}
PRO li     {font-size:8pt; color:black; padding-left:4px; padding-right:4px; padding-bottom:2px;}
PRO th     {font-weight:bold; color:white; background:#0066CC; padding-left:4px; padding-right:4px; padding-bottom:2px;}
PRO td     {color:black; background:#fcfcf0; vertical-align:top; border:1px solid #cccc99;}
PRO td.c   {text-align:center;}
PRO font.n {font-size:8pt; font-style:italic; color:#336699;}
PRO font.f {font-size:8pt; color:#999999; border-top:1px solid #cccc99; margin-top:30pt;}
PRO </style>
PRO
PRO <script type="text/javascript" src="https://www.google.com/jsapi"></script>
PRO <script type="text/javascript">
PRO google.load("visualization", "1", {packages:["corechart"]})
PRO google.setOnLoadCallback(drawChart)
PRO
PRO function drawChart() {
PRO var data = google.visualization.arrayToDataTable([
/* add below more columns if needed (modify 3 places) */
PRO ['Date Column', 'Number Column 1']
/****************************************************************************************/
WITH
my_query AS (
/* query below selects one date_column and a small set of number_columns */
SELECT --TRUNC(time_id, 'HH24') date_column /* preserve the column name */
       --TRUNC(time_id, 'DD') date_column /* preserve the column name */
       TRUNC(time_id, 'MM') date_column /* preserve the column name */
       , SUM(amount_sold) number_column_1 /* add below more columns if needed (modify 3 places) */
  FROM sh.sales
 GROUP BY
       --TRUNC(time_id, 'HH24') /* aggregate per hour, but it could be any other */
       --TRUNC(time_id, 'DD') /* aggregate per day, but it could be any other */
       TRUNC(time_id, 'MM') /* aggregate per month, but it could be any other */
/* end of query */
)
/****************************************************************************************/
/* no need to modify the date column below, but you may need to add some number columns */
SELECT ', [new Date('||
       TO_CHAR(q.date_column, 'YYYY')|| /* year */
       ','||(TO_NUMBER(TO_CHAR(q.date_column, 'MM')) - 1)|| /* month - 1 */
       --','||TO_CHAR(q.date_column, 'DD')|| /* day */
       --','||TO_CHAR(q.date_column, 'HH24')|| /* hour */
       --','||TO_CHAR(q.date_column, 'MI')|| /* minute */
       --','||TO_CHAR(q.date_column, 'SS')|| /* second */
       ')'||
       ','||q.number_column_1|| /* add below more columns if needed (modify 3 places) */
       ']'
  FROM my_query q
 ORDER BY
       date_column
/
/****************************************************************************************/
PRO ]);
PRO
PRO var options = {
PRO backgroundColor: {fill: '#fcfcf0', stroke: '#336699', strokeWidth: 1},
PRO explorer: {actions: ['dragToZoom', 'rightClickToReset'], maxZoomIn: 0.1},
PRO title: '&&chart_title.',
PRO titleTextStyle: {fontSize: 16, bold: false},
PRO focusTarget: 'category',
PRO legend: {position: 'right', textStyle: {fontSize: 12}},
PRO tooltip: {textStyle: {fontSize: 10}},
PRO hAxis: {title: '&&xaxis_title.', gridlines: {count: -1}},
PRO vAxis: {title: '&&vaxis_title.' &&vaxis_baseline., gridlines: {count: -1}}
PRO }
PRO
PRO var chart = new google.visualization.LineChart(document.getElementById('chart_div'))
PRO chart.draw(data, options)
PRO }
PRO </script>
PRO </head>
PRO <body>
PRO <h1>&&report_title.</h1>
PRO &&report_abstract_1.
PRO &&report_abstract_2.
PRO &&report_abstract_3.
PRO &&report_abstract_4.
PRO <div id="chart_div" style="width: 900px; height: 500px;"></div>
PRO <font class="n">Notes:</font>
PRO <font class="n">&&chart_foot_note_1.</font>
PRO <font class="n">&&chart_foot_note_2.</font>
PRO <font class="n">&&chart_foot_note_3.</font>
PRO <font class="n">&&chart_foot_note_4.</font>
PRO <pre>
L
PRO </pre>
PRO <br>
PRO <font class="f">&&report_foot_note.</font>
PRO </body>
PRO </html>
SPO OFF;
SET HEA ON LIN 80 NEWP 1 PAGES 14 FEED ON ECHO OFF VER ON LONG 80 LONGC 80 WRA ON TRIMS OFF TRIM OFF TI OFF TIMI OFF ARRAY 15 NUM 10 NUMF "" SQLBL OFF BLO ON RECSEP WR;

 

 

Written by Carlos Sierra

July 28, 2014 at 2:34 pm

eAdam

with 9 comments

Enkitec’s Oracle AWR Data Mining Tool

eAdameAdam is a free tool that extracts a subset of data and metadata from an Oracle database with the objective to perform some data mining using a separate staging Oracle database. The data extracted is relevant to Performance Evaluations projects. Most of the data eAdam extracts is licensed by Oracle under the Diagnostics Pack, and some under the Tuning Pack. Therefore, in order to use this eAdam tool, the source database must be licensed to use both Oracle Packs (Tuning and Diagnostics).

To a point, eAdam is similar to eDB360; both access the Data Dictionary in order to produce some reports. The key difference is that eDB360 generates all the reports (after doing some intensive processing) at the source database, while eAdam simply extracts a set of flat files into a TAR file, using a very light-weight script, delaying all the intensive processing for a later time and on a separate staging system. This feature can be very attractive for busy systems where the amount of processing of any external monitoring tool needs to be minimized.

On the source system, eAdam only needs to execute a short script to extract the data and metadata of interest, producing a dense TAR file. On a staging system, eAdam does the heavy lifting, requiring the creation of a repository, the load of this repository and finally the computation of meaningful reports. The processing of the TAR file into the staging system is usually performed by the requestor, using a lower-level database, or a remote one.

The list of objects eAdam extracts as flat files from the source database includes the following:

dba_hist_active_sess_history
dba_hist_database_instance
dba_hist_event_histogram
dba_hist_osstat
dba_hist_parameter
dba_hist_pgastat
dba_hist_sga
dba_hist_sgastat
dba_hist_snapshot
dba_hist_sql_plan
dba_hist_sqlstat
dba_hist_sqltext
dba_hist_sys_time_model
dba_hist_sysstat
gv$active_session_history
gv$log
gv$sql_monitor
gv$sql_plan_monitor
gv$sql_plan_statistics_all
gv$sql
gv$system_parameter2
v$controlfile
v$datafile
v$tempfile

eAdam works on 10gR2, 11gR2, and on higher releases of Oracle; and it can be used on Linux or UNIX Platforms. It has not been tested on Windows. An eAdam sample output is available at this Dropbox location; after downloading the sample output, look for the 0001_eadam36_N_dbname_index.html file and start browsing.

Instructions – Source Database

Download the tool, uncompress the master ZIP file, and look for file eadam-master/source_system/eadam_extract.sql. Review and execute this single and short script connecting to the source database as SYS or DBA. Locate the TAR file produced, and send it to the requestor.

Be aware that the TAR file produced by the extraction process can be large, so be sure you execute this extract script from a directory with at least 10 GBs of free space. Common sizes of this TAR file range between 100 MBs and 1 GB. Execution time for this extraction process may exceed 1 hour, depending on the size of the Data Dictionary.

Instructions – Staging Database

Be sure you have both the eAdam tool (eadam-master.zip) and the TAR file produced on a source system. Your staging database can be of equal, higher or lower release level than the source, but equal or higher is recommended. The Platform can be the same or different.

To install, load and report on the staging database, proceed with the following steps:

  1. Create on the staging system a file directory available to Oracle for read and write. Most probably you want to create this directory connecting to OS as Oracle and create a new directory like /home/oracle/eadam-master. Put in there the content of the eadam-master.zip file.
  2. Create the eAdam repository on the staging database. This step is needed only one time. Follow instructions from the eadam_readme.txt.  Basically you need to execute eadam-master/stage_system/eadam_install.sql connected as SYS. This script asks for 4 parameters: Tablespace names for permanent and temporary schema objects, and the username and password of the new eAdam account. For the username I recommend eadam, but you can use any valid name.
  3. Load the data contained in the TAR file into the database. To do this you need first to copy the TAR file into the eadam-master/stage_system sub-directory and execute next the stage_system/eadam_load.sql script while on the stage_system sub-directory, and connecting as SYS. This script asks for 4 parameters. Pass first the directory path of your stage_system sub-directory, for example /home/oracle/eadam-master/stage_system (this sub-directory must contain the TAR file). Pass next the username and password of your eadam account as you created them. Pass last the name of the TAR file to be loaded into the database.
  4. The load process performs some data transformations and it produces at the end an output similar to eDB360 but smaller in content. After you review the eAdam output, you may decide to generate new output for shorter time series, in such case use the eadam-master/stage_system/eadam_report.sql connecting as the eadam user. This reporting process asks for 3 parameters. Pass the EADAM_SEQ_ID which identifies your particular load (a list of values is displayed), then pass the range of dates using format YYYY-MM-DD/HH24:MI, for example 2014-07-27/17:33.

Download

EADAM @ GitHub is available as free software. You can see its eadam_readme.txt, license.txt or any other piece of the tool before downloading it. Use this link eadam-master.zip to actually download eAdam as a compressed file.

Feedback

Please post your feedback about this eAdam tool at this blog, or send and email directly to the tool author: Carlos Sierra.

Written by Carlos Sierra

July 27, 2014 at 6:25 pm

eDB360

with 23 comments

Enkitec’s Oracle Database 360-degree View

eDB360_206_135_csEDB360 is a free tool that executes on an Oracle database and produces a compressed file which includes a large set of small Reports. This set of Reports provides a 360-degree view of an Oracle Database. EDB360 is mostly used for one of the following 3 reasons, listed here in order of frequency of use: 1) Keystone of an Oracle database Health-Check. 2) Kick-off for an Oracle database Performance Evaluation. 3) High-level view of System Resources demand and utilization for an Oracle database Sizing and Provisioning project.

Usually, Developers, Sys Admins and Consultants are not given open access to a database in a Production environment. This eDB360 free tool helps approved users to become familiar with an Oracle database in a non-intrusive way. Without installing anything on the database, the eDB360 tool connects to an Oracle database and produces a large set of flat files that can be reviewed offline while using an HTML browser or a Text editor.

EDB360 can be executed by someone with very limited access to an Oracle database (i.e. a Developer, Sys Admin or Consultant with just query access to the Data Dictionary views); or if executed by an authorized DBA, there is no actual need to provide any additional access to the Oracle database to the party requesting eDB360.

EDB360 works on 10gR2, 11gR2, and on higher releases of Oracle; and it can be used on Linux or UNIX Platforms. It has not been tested on Windows. An eDB360 sample output is available at this Dropbox location; after downloading the sample output, look for the 0001_edb360_dbname_index.html file and start browsing.

Instructions

Download the eDB360 tool and review the readme.txt file included. Uncompress the eDB360 master ZIP file on the Database Server of interest. Navigate to the main eDB360 (master) directory and execute script edb360.sql connected as SYS or any other account with access to the Data Dictionary views (a DBA account is not required but it is preferred).

Execution time for eDB360 may exceed 1 hour, depending on the size of the Data Dictionary. And the size of the output may reach 1 GB, so be sure you execute this tool from a file system directory with at least 1 GB or free space. Common sizes of the output range between 10 and 100 MB.

EDB360 has only one execution parameter:

  1. Oracle Pack License: A big portion of the information presented by eDB360 comes from Oracle’s Automatic Workload Repository (AWR), and AWR is licensed by Oracle under the Diagnostics Pack. A small part of the output of eDB360 comes from the SQL Monitoring repository, which is part of the Oracle Tuning Pack. This parameter accepts one of 3 values: “T”, “D” or “N”. If you database is licensed under the Oracle Tuning Pack, enter then the value of “T”. If your database is not licensed to use the Oracle Tuning Pack but it is licensed to use the Oracle Diagnostics Pack, enter “D” then. If your site is not licensed on any of these two Oracle Packs, enter “N” then. Be aware that a value of “N” reduces substantially the content and value of the output. Thus the preferred parameter value is “T” (Oracle Tuning Pack).

Sample

# unzip edb360-master.zip
# cd edb360-master
# sqlplus / as sysdba
SQL> @edb360.sql T

Download

EDB360 @ GitHub is available as free software. You can see its readme.txt, license.txt or any other piece of the tool before downloading it. Use this link edb360-master.zip to actually download eDB360 as a compressed file.

Feedback

Please post your feedback about this eDB360 tool at this blog, or send and email directly to the tool author: Carlos Sierra.

Written by Carlos Sierra

July 27, 2014 at 6:14 pm

Posted in AWR, edb360, Health-Checks, Tools

Why using SQLTXPLAIN

leave a comment »

Every so often I see on a distribution list a posting that starts like this: “I upgraded my application from database release X to release Y and now many queries are performing poorly, can you tell why?”

As everyone else on a distribution list, my first impulse is to make an educated guess permeated by a prior set of experiences. The intentions are always good, but the process is painful and time consuming. Many of us have seen this kind of question, and many of us have good hunches. Still I think our eagerness to help blinds us a bit. The right thing to do is to step back and analyze the facts, and I mean all the diagnostics supporting the observation.

What is needed to diagnose a SQL Tuning issue?

The list is large, but I will enumerate some of the most important pieces:

  1. SQL Text
  2. Version of the database (before and after upgrade)
  3. Database parameters (before and after)
  4. State of the CBO Statistics (before and after)
  5. Changes on Histograms
  6. Basics about the architecture (CPUs, memory, etc.)
  7. Values of binds if SQL has them
  8. Indexes compare, including state (visible?, usable?)
  9. Execution Plan (before and after)
  10. Plan stability? (Stored Outlines, Profiles, SQL Plan Management)
  11. Performance history as per evidence on AWR or StatsPack
  12. Trace from Event 10053 to understand the CBO
  13. Trace from Event 10046 level 8 or 12 to review Waits
  14. Active Session History (ASH) if 10046 is not available

I could keep adding bullets to the list, but I think you get the point: There are simply too many things to check! And each takes some time to collect. More important, the state of the system changes overtime, so you may need to re-collect the same diagnostics more than once.

SQLTXPLAIN to the rescue

SQLT or SQLTXPLAIN, has been available on MetaLink (now MOS) under note 215187.1 for over a decade. In short, SQLT collects all the diagnostics listed above and a lot more. That is WHY Oracle Support uses it every day. It simply saves a lot of time! So, I always encourage fellow Oracle users to make use of the FREE tool and expedite their own SQL Tuning analysis. When time permits, I do volunteer to help on an analysis. So, if you get to read this, and you want to help yourself while using SQLT but feel intimidated by this little monster, please give it a try and contact me for assistance. If I can help, I will, if I cannot, I will let you know.

Conclusion

It is fun to guess WHY a SQL is not performing as expected, and trying different guesses is educational but very time consuming. If you want to actually find root causes before trying to fix your SQL, you may want to collect relevant diagnostics. SQLT is there to help, and if installing this tool is not something you can do in a short term, consider then SQL Health-Check SQLHC.