Kerry Osborne's Oracle Blog

I posted earlier about the ability to flush a single SQL statement out of the shared pool in 11g (also back ported to 10.2.0.4 with a bit of extra work) here. If you are on an earlier release of Oracle though, you can accomplish the same thing by creating an outline on the statement using the DBMS_OUTLN.CREATE_OUTLINE procedure. I just discovered this recently, so let me know if I just missed this trick. Anyway, prior to noticing this affect of creating an outline, my best options to flush a statement were:

• flush the shared pool – not a very appealing option in a production environment (although I see almost the same affect frequently at sites that gathering stats every night).
• modify an object that the statement depends on – I usually would add a comment to one of the tables used by the statement. Unfortunately, all statements that use the table will be flushed, so this technique can also be a little hard on a production system, but it’s certainly better than flushing the whole shared pool. 

So I wrote a little script (like I always do) and called it flush_sql10.sql. There are a couple of things to be aware of with it.

1. I don’t like having to find the hash_value that the create_outline procedure uses, so I prompt for the sql_id and then let the script find the hash_value.
2. The create_outline procedure requires a child number, but the flushing affect is not limited to the specified child. All children for the specified statement will be flushed.
3. The script drops the outline after creating it (since the purpose is to flush the statement, not to create an outline). This part is a little dicey since the create_outline procedure does not return an identifier for the outline that gets created. Nor does it allow you set a name for the outline. So I coded it to drop the most recently created outline (which should be sufficient, since it would be highly unlikely that more than one person would be creating outlines at the same time). But wait, don’t answer yet, I also limited the drop to outlines created in the last 5 seconds. Bottom line, it is unlikely that an unintended outline would be accidentally dropped by the script. (you have however been forewarned!)
4. There’s no error checking. Any errors stop execution of the script and are passed back to the user. The most common error is to not give it a valid SQL_ID, CHILD_NO combination. In this case the create_outline procedure fails and the script exits with a “no data found” message.

Here’s an example:

> sqlplus / as sysdba

SQL*Plus: Release 10.2.0.3.0 - Production on Fri Dec 12 08:31:08 2008

Copyright (c) 1982, 2006, Oracle.  All Rights Reserved.


Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - Production
With the Partitioning, OLAP and Data Mining options

SQL> @find_sql
Enter value for sql_text: %skew%
Enter value for sql_id:

SQL_ID         CHILD  PLAN_HASH      EXECS     AVG_ETIME      AVG_LIO INVALIDATIONS    SQL_TEXT
------------- ------ ---------- ---------- ------------- ------------ ------------- -----------------------------------------------------
0gza16w5ka67q      0 1528838287          1           .01          249             0 SELECT   count(*)    FROM kso.skew where pk_col < 10
688rj6tv1bav0      0 3723858078          1          2.15       37,270             1 select avg(pk_col) from kso.skew where col1 = 1
688rj6tv1bav0      1  568322376          1          5.09      173,731             1 select avg(pk_col) from kso.skew where col1 = 1
7cbu7dgt0vh6y      0 1528838287          1           .00          226             0 select count(*) from kso.skew where pk_col < 10

SQL> @flush_sql_ol

Session altered.

Enter value for sql_id: 688rj6tv1bav0
Enter value for child_number: 1

SQL Statement 688rj6tv1bav0 flushed.
(Note also that outline SYS_OUTLINE_08121120170934217 was dropped.)

PL/SQL procedure successfully completed.

SQL> @find_sql
Enter value for sql_text: %skew%
Enter value for sql_id:

SQL_ID         CHILD  PLAN_HASH      EXECS     AVG_ETIME      AVG_LIO INVALIDATIONS    SQL_TEXT
------------- ------ ---------- ---------- ------------- ------------ ------------- -----------------------------------------------------
0gza16w5ka67q      0 1528838287          1           .01          249             0 SELECT   count(*)    FROM kso.skew where pk_col < 10
7cbu7dgt0vh6y      0 1528838287          1           .00          226             0 select count(*) from kso.skew where pk_col < 10

I went to the Dallas 100 awards banquet last night. The Dallas 100 is an annual award for the fastest growing privately held companies that are based in the Dallas / Fort Worth area. Enkitec was ranked 42nd in our first year to be eligible. They have it every year at the Morton Meyerson. It’s a beautiful place by the way, with one of the worlds greatest pipe organs.

Ray Hunt was the speaker. He had a couple of insightful things to say (of course I’ll have to paraphrase).

He said the oil business was the only business he was aware of where you could look forward at the first of every year and know that 90% of the decisions you’ll make that year will be wrong. Which means that the other 10% have to make up for all those wrong decisions and still provide a reasonable profit to the business. He said his background in the oil business made him very tolerant of failure and that America in general was very tolerant of failure which he thought was a good thing. He then told a story about one of his managers telling him that his department had not made any mistakes in the previous 12 months. To Ray that meant one of two things (and both were bad). Either the manager had lost complete touch with reality, or his department was not being aggressive enough.

He went on to list his top 5 attributes of successful companies. He said he thought the most important characteristic of a successful company was it’s Culture.

He defined Culture as the combination of the shared values and the shared work ethic of a group of individuals.

Other attributes that made his top 5 list were:

• Adaptibility – the ability to change
• Agility – the ability to move quickly
• Differentiation – the ability to recognize, retain, and enhance that which sets you apart
• Contrarian – the ability to question the accepted practices

Here’s a very brief story in response to Doug Burns’ post at his blog calling for stories on Human Error.

My very first job out of college was with a large oil company that had Oracle running on bunch of VAX/VMS systems. We had a lot of code written in FORTRAN with OCI calls (this was back in the early 80’s, so no pre-compilers yet). I was working late one night from home, which in itself was an unusual thing because not too many people were able to work remotely at that time. We only had 1200 baud modems for crying outloud, so it was painful to do much of anything remotely. At any rate, I was working on a program with some kind of iterative processing which took a while to complete. So I’d make a few changes and run it, make a few changes and run it. Well I noticed that the execution time slowed down somewhat and so I went looking to see what else was running on the system. (brief digression: I had become a neophyte sys admin due to my being the Oracle DBA and needing to have some system privileges for doing upgrades and whatnot) So I had a look to see what might be slowing my program down and sure enough there was a batch job running that was really using a lot of cpu. Well I had learned about the ability of VMS to set process priorities and so I thought to myself, “that batch job has all night to run it shouldn’t be slowing me down right now”. So I determined to change the priorities so my program would not be competing so heavily with the batch job. Unfortunately, instead of lowering the priority of the batch process, I jacked the priority of my process way up. (you’ll see why I say “unfortunately” in a minute) So anyway, the priority change worked out great. My program executions began running even faster than they had prior to the batch job kicking off. So I went back to my programming routine. Make a few changes, execute the program, check the results, make a few changes, execute the program, check the results… until I executed the program and it didn’t come back. I remember thinking, “Uh oh, I think I messed up the check for getting out of that loop”. So I thought, “well I’ll just ctl-C out and fix it”. Unfortunately, in a stupendous example of Murphy’s Law,  it was at just this point that my modem lost it’s connection. Great! So I tried to reconnect. The modem was able to establish a connection, but the machine was so busy running the process with the insanely high priority that it didn’t have enough spare CPU to log another process in. (Unlike most systems today, VMS had a very hard priority system. The process with the highest priority basically stayed on the CPU as long as they wanted – oh and by the way, there was only the one CPU) So anyway, the program ended up running most of the night and only stopped because it filled up the disk with a log file that it was writing. Needless to say, the real sys admins were not too happy with me the next morning when I showed up at work.

The best Oracle conference in the galaxy.

I’ve attended the last 4 years in a row and I have to say that it’s been far and away the best conference or training event that I’ve ever participated in. Add to that the extremely high quality of the people in attendance and you get an awesome event. 

The 2009 Symposium will be held in Dallas (as always), March 8-12. Chris Date will be giving the key note address. He is one of the founding fathers of Relational Databases and I am very interested to hear what he has to say. 

I must say I am extremely honored to be able to present at this years symposium, and humbled to be in the company of the other presenters. Here’s a link to the speakers page for this years event. And here’s a link to the sign up page.

Hope to see you there!

Oracle uses the BITAND function heavily (over 1000 times in the catalog.sql script alone as of 10.2.0.4). It’s used to determine whether a particular bit is set or not.

Here’s a link to 11gR1 documentation on the BITAND function. The function takes 2 arguments and performs these basic steps:

1. Converts the 2 arguements to binary (n-bit two’s complement binary integer value)
2. Performs a standard bitwise AND operation on the two strings
3. Converts the binary result back to decimal

So what’s a standard bitwise AND operation actually do?

Well it basically does a logical AND of two bit strings. If the values in any position are both 1’s, then the result will have a 1 in that position, otherwise the result will have a 0 in that position. Here’s a link to the Wikipedia entry on bitwise operations in case you want more information.

Here’s an example:

   
    0101
AND 1001
  = 0001

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