Tag: SQL

Community, SQL | PLSQL, Tools

Guru99: PL/SQL 101 Completely Free!

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Hey all!
Just passing by today to share something I found really inetresting, and the best: it’s all free!
Do you know Guru99?

It’s a preety nice repository with lots of free tutorials and guides for PLSQL, SQL and several other languages, plus some other IT-related knowledge, like Big Data, PMP and etc.

It’s not rare to have people asking me “How to Start learning SQL” or saying “All material (including grepora :D) is too much specific, we don’t have good general documentation”.
Even Oracle having a pretty nice documentation on the products and features, general concepts are usually forgotten. Aaaaand, now I have something to link on those cases! 😀

Having a look on Guru99, First I found this guide PL/SQL First Program: Hello World, including detailed steps on:
– How to access SQL* Plus
– Connecting to Database
– How to write a simple program using PL/SQL
– Declaring and usage of variables in program
– Commenting Codes

Then found an entire category PL/SQL Tutorials. Talking to Alex (Editor), seems over 120 hours were spent on it. And they were well spent, the material is really very easy to read and understand. Chapters on this Course are:
1. Introduction to PL/SQL
2. Blocks in PL/SQL
3. PL SQL First Program: Hello World
4. PL/SQL Data Types
5. Complex Data Types in PL/SQL
6. PL/SQL Decision Making Statements
7. Loops in PL/SQL
8. Subprograms: Procedures and Functions in PL/SQL
9. Exception Handling in PL/SQL
10. SQL in PL/SQL
11. Packages in PL/SQL
12. Triggers in PL/SQL
13. Object Types in PL/SQL
14. Dynamic SQL in PL/SQL
15. Nested Blocks in Pl/Sql
16. PL/SQL Identifiers

More“Guru99: PL/SQL 101 Completely Free!”

Database, Errors and Bugs, Performance, SQL | PLSQL

Purging a SQL Cursor in 10g

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Hello all,
Having issues to purge SQL Cursor in a 10g database?

DBMS_SHARED_POOL.PURGE is available from 10.2.0.4 on, but according to “DBMS_SHARED_POOL.PURGE Is Not Working On 10.2.0.4 (Doc ID 751876.1)”, it is event-protected.
This means you need to set event 5614566 to be able to use the purge.

Example:

sys@PRODB10> select count(*) from v$sqlarea where sql_id='gbaq7x7myqxjw';

  COUNT(*)
----------
         1

sys@PRODB10> exec dbms_shared_pool.purge('00000003B0898118,1807156054','C')

PL/SQL procedure successfully completed.


sys@PRODB10> select count(*) from v$sqlarea where sql_id='gbaq7x7myqxjw';

  COUNT(*)
----------
         1

sys@PRODB10> alter session set events '5614566 trace name context forever';

Session altered.

sys@PRODB10> exec dbms_shared_pool.purge('00000003B0898118,1807156054','C')

PL/SQL procedure successfully completed.

sys@PRODB10> select count(*) from v$sqlarea where sql_id='gbaq7x7myqxjw';

  COUNT(*)
----------
         0
Database, SQL | PLSQL

Purge Recycle Bin Older than…

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Hello all!

Have your recyclebin being full/big but don’t want to make a complete “PURGE RECYCLE BIN;”?
Want remove only older than x days (like older than 30 days)?

Please don’t:

DELETE from DBA_RECYCLEBIN where droptime<sysdate-30;
PURGE DBA_RECYCLEBIN where droptime<sysdate-30;

A good way to perform that is to execute output from:

# 30 Days
select 'purge table '||owner||'."'||OBJECT_NAME||'";' 
from dba_recyclebin where type='TABLE' 
and to_date(droptime,'YYYY-MM-DD:HH24:MI:SS')<sysdate-30;

# 30 minutes
select 'purge table '||owner||'."'||OBJECT_NAME||'";' 
from dba_recyclebin where type='TABLE' and 
to_date(droptime,'YYYY-MM-DD:HH24:MI:SS')<sysdate-(30/(24*60));

There is some reference here too:
How To Drop / Delete / Purge Recyclebin or DBA_RECYCLBIN For Objects Older Than x Days/minutes or selective purge of objects from recycle bin (Doc ID 1596147.1)

Hope it help you!
Cheers!

Database, SQL | PLSQL

Oracle Database 9i: Where is my SQL_ID? Which SQL is in lock?

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Struggling with that, right?
As you know, in Oracle Database 9i the view V$SESSION doesn’t have SQL_ID column…
So how to map SQLs in my database? And, for example, how to get the SQLs causing a lock?

In the end of the day, the SQL_ID is only a representation of the hash_value of an SQL. You can even make the translation from SQL_ID to Hash Value as you can check on this post by Tanel Poder.

Ok, but I have to map which sql is causing the lock in my 9i database, how can I do that?

Here it goes:

If session status is ACTIVE:

SELECT s1.sql_text from v$sqlarea s1,v$session s2 where s2.SID=&sid and s2.SQL_ADDRESS = s1.ADDRESS

If session status is INACTIVE:

SELECT s1.sql_text from v$sqlarea s1,v$session s2 where s2.SID=&sid and s2.prev_sql_addr = s1.ADDRESS

You’re welcome! 😉

See you next week!

Database, Performance, SQL | PLSQL

Parameter Workarounds: Changing your Entire Database’s Behavior Because of a Query

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This post is just a reflection, basically based on my last post about Adaptive Query Optimization/SQL Plan Directives. Several times we find some situations that can be solved by setting a parameter (likely a “_”) and we just proceed with an “alter system” disregarding about all the impact of this.

This is specially important when talking about “optimizer” parameters even for bugs causing ORA-600’s or performance issues… Changing those parameters in system will affect not only the SQL with the error but all SQLs in database, which may cause a really bad effect in some cases.

bad-idea-sign

Ok Matheus, but what can I do?
Let’s to the obvious and generally applied methods:

More“Parameter Workarounds: Changing your Entire Database’s Behavior Because of a Query”

Database, Errors and Bugs, Migration | Upgrades | Patching, Performance

Adaptive Query Optimization: SQL Plan Directives Causing High CPU after 12c Upgrade

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Hello all!

As DBAs we are always being recommended by Oracle and also recommending to clients to update their databases, but we have to be aware about new features and their effects. This is the case of Adaptive Query Optimization and in this particular case on SQL Plan Directives.

SQL Plan Directives are one of the functionalities that compose the Adaptive Query Optimization in Oracle Database 12c. The basic idea is pretty interesting: The SQL Optimizer keeps reviewing bad (“suboptimal”, as they like to say) plans, tipically incorrect cardinality estimations and generates SQL plan directives, like for missing histograms or extended statistics.

In my case, just after the upgrade to 12c (made on Jan 27th), the CPU usage increased for the same report always ran in the database:

12c_upgrade

Ok, how to check it?

More“Adaptive Query Optimization: SQL Plan Directives Causing High CPU after 12c Upgrade”

Database, Security, SQL | PLSQL

Vulnerability: Decrypting Oracle DBlink password (<11.2.0.2)

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Hi all,
It’s not a new vulnerability, but a good thing to have personal note about it. Besides the security problem, it can save you from situations you need but don’t have the database link password.
It works only if the database link was created pre-11.2.0.2.

The vulnerability only is exposed if user has one of the follow privileges:
SYS
SYSDBA
DBA
SYS WITHOUT SYSDBA
SYSASM
EXP_FULL_DATABASE
DATAPUMP_EXP_FULL_DATABASE
DATAPUMP_IMP_FULL_DATABASE

combo_lock_page.jpg

Starting with 11.2.0.2, Oracle changed the hashes format for database link passwords, solving this vulnerability. But it only apply to dblinks created in this version or higher.
If you have dblink created when database was on 11.2.0.1, for example, and upgrade the database for 11.2.0.4, the problem remains until you recreate the database link.

So, if you are upgrading database from 11.2.0.1 or lower to 11.2.0.2 or higher, remember to reacreate database links!

The vulnerability was exposed in 2012 by Paul Wright. Here is his PoC.
And there is his post.

To make it different, below I made the same test (using a PLSQL block, to make it prettier) with an upgraded database, from 11.2.0.1 to 11.2.0.4:

testdb11204> select passwordx from sys.link$ where name='MY_DBLINK';

PASSWORDX
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0540C5B8090D021649C5C614E8E0C242AF33F71C08C535900C
1 row selected.
testdb11204> set serveroutput on
testdb11204> declare
2   db_link_password varchar2(100);
3  begin
4   db_link_password := '0540C5B8090D021649C5C614E8E0C242AF33F71C08C535900C';
5   dbms_output.put_line ('Password: ' || utl_raw.cast_to_varchar2 ( dbms_crypto.decrypt ( substr (db_link_password, 19) , dbms_crypto.DES_CBC_PKCS5 , substr (db_link_password, 3, 16) ) ) );
6  end;
7  /
Password: P4SSW0RD

Note that the simple upgrade does not solve the question. Is needed to recreate database link.

Matheus.

Database, Performance, SQL | PLSQL

Oracle TPS: Evaluating Transaction per Second

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Sometimes this information has some ‘myth atmosphere’… Maybe because of that Oracle doesn’t have this information very clear and it’s not the most useful metric.
But for comparison to another systems and also to performance/’throughput’ with different infrastructure/database configuration, it can be useful.

It can be seen by AWR on “Report Summary” section, on “Load Profile”, “Transactions” item:

awr_tps

But if you want to calculate it through SQL query?
And if you want to have a historic from this metric?

I found a reference for this calculation here, using v$sysstat.
It’s the only reference I found, and it on 10g documentation… It refers this metric as:

Number of Transactions = (DeltaCommits+DeltaRollbacks)/Time

It also refers as DeltaCommits and DeltaRollbacks, respectively, “user commits” and user “rollbacks”.

Where it goes a possible SQL to do that:

WITH hist_snaps
AS (SELECT instance_number,
snap_id,
round(begin_interval_time,'MI') datetime,
(  begin_interval_time + 0 - LAG (begin_interval_time + 0)
OVER (PARTITION BY dbid, instance_number ORDER BY snap_id)) * 86400 diff_time
FROM dba_hist_snapshot), hist_stats
AS (SELECT dbid,
instance_number,
snap_id,
stat_name,
VALUE - LAG (VALUE) OVER (PARTITION BY dbid,instance_number,stat_name ORDER BY snap_id)
delta_value
FROM dba_hist_sysstat
WHERE stat_name IN ('user commits', 'user rollbacks'))
SELECT datetime,
ROUND (SUM (delta_value) / 3600, 2) "Transactions/s"
FROM hist_snaps sn, hist_stats st
WHERE     st.instance_number = sn.instance_number
AND st.snap_id = sn.snap_id
AND diff_time IS NOT NULL
GROUP BY datetime
ORDER BY 1 desc;

I like to use PL/SQL Developer to see this kind of data. And it regards us to make very good charts very quickly. I try it in a small database here, just for example:

7days_tps

Jedi Master Jonathan Lewis wrote a good post about Transactions and this kind of AWR metric here.

See ya!
Matheus.