Pctfree=0-table high free blockspace ratio?

I have been looking at Metalink and Asktom but could not find what I was looking for so perhaps one of you can help me.
I have a table that seems to keep on growing when no data is added.
Details:
- db block size = 8k
- only deletes and inserts are done on this table (mimicing updates)
- pctfree=0 and pctused=99.
- inserted 972057 records
- avg row size is 147 bytes
- total data size 142725354 bytes (using vsize on all columns/records)
- initially, after the insert, I have 171966464 bytes reserved (user_segments)
- the difference between the two expressed over the actual data size is 0.2 (for each byte I insert 0.2 of a byte is reserved as extra empty space/overhead).
Now I've created a procedure (test environment) that randomly(!) copies a record in a temporary table, deletes the original and then inserts the record from the temporary table into the base table again. During this operation, only the primary gets changed (sequence/trigger). In theory this should not make the table increase other than for storing the potentially bigger primary key (and thus storing the whole row in a different block).
After 1.36 mln of these deletes/inserts, the primary key has doubled in size (user_segments) and the table has increased 60%.
If i do 80000 more deletes/inserts, the primary key stays stable, but the table seems to keep increasing in size.
After more than 1.44 mln deletes/inserts, the ratio is almost at 0.7 and it doesn't seem to get stable (let alone decline).
My questions:
1) why does Oracle need so much extra space? Surely a 0.3 or 0.4 should be way enough in this case?
2) when does this end?
Thanx for any assistance/references you can give me.
Lennert

yes. Average is 147 bytes. However, the record that gets deleted and inserted is identical with the exception of the PK (that is replaced by a number from a sequence).

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Message was edited by:
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sono99 wrote:
Hi,s
first of, let me start by saying that there were many things in your post that you mentioned that I could no understand. 1. Because i am not an Oracle Expert, i use whatever RDBMS whenever i need to. 2. Because another problem has come up and, right now, i cannot inform myself to be able to comprehend it all.Well, could it be that you need to understand the database you are working on in order to comprehend it? That is why we strongly advise you to read the concepts manual first, you need to understand the architecture that Oracle uses, as well as the basic concepts of how oracle does locking and maintains read consistency. It does these different than other database engines, and some things become nonsense if looked at from the viewpoint of a single user.
>
quote:
It would be useful to see the execution plan jhust in case you have simplified the problem so much that a critical detail is missing.
First, the query code:
2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:>SQL> CREATE TABLE FAVFRIEND
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 2 NOLOGGING TABLESPACE TARGET
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 3 AS
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 4 SELECT ID as USRID, FAVF1 as FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 5 UNION ALL
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 6 SELECT ID as USRID, FAVF2 AS FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 7 UNION ALL
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 8 SELECT ID as USRID, FAVF3 AS FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 9 UNION ALL
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 10 SELECT ID as USRID, FAVF4 AS FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 11 UNION ALL
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 12 SELECT ID as USRID, FAVF5 AS FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 13 ;
Now, Althought it is clear from the query that the statement is executed with the NOLOGGiNG, i have disabled the logging entirely for the tablespace.There are certain rules about nologging that may not be obvious. Again, this derives from the basic Oracle architecture, and if you use the wrong definitions of things like logging, you will be led down the primrose path to confusion.
>
Futhermore, yes, the RDBMS is a test RDBMS... I have droped the database a few times... And I am constantly deleting an re-inserting data into the source database table named PROFILE.>
I also make sure do check all the datafile statistics, and for this query the amount of RedoLog, Undo "Log", Templife used is negligible, practically zero.Create table is DDL, which has implied commits before and afterwards. There is a lot going on, some of it dependent on the volume of data returned. The Oracle database writer writes things out when it feels like it, there are situations where it might just leave it in memory for a while. With nologging, Oracle may not care that you can't perform recovery if it is interrupted. So you might want to look into statspack or EM to tell you what is going on, the datafile statistics may not be all that informative for this case.
>
Most of the I/O is reading, a few of the I/O is writing.
My idea is not to optimize this query, it is to understand how it performs. Well, have you read the Concepts manual?
I have other implementations to test, namely I having trouble with one of them.
Furthermore, I doubt the query Plan Oracle is using actually involves tablescans (as I I'd like it to do); because in the Wait Events, most of the wait time for this query is spent doing "db file scattered read". And I think this is different from a tablescan.Please look up the definition of [db file scattered read|http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/instance_tune.htm#sthref703].
>
Do you really have to use sessions external to the query session ? Can you query v$mystat joined to v$statname from the session itself.
No, I don't want to that!
I avoid as much as possible having the code I execute being implemented in java. Why do you think java has anything to do with this? In your session, desc v$mystat and v$statname, these are views you can look at.
When i can avoid it I don't query the database directly through JDBC, i use the RDBMS command line client, which is supposed to be very robust. Er, is that sqlplus?
So yes, I only connect to the database with JDBC... in very last session.
Of course, I Could Have put both the gather stats before query and gathers stats after query a single script: the script that would be also runing the query.
But that would cause me a number of problems, namely some of the SQL i build has to be implemented dynamically. And I don't want to be replicating the snapshoting code into every query script I make. This way I have one sql with the snapshoting scripts; and multiple scripts for running each query. I avoid code replication in this manner.Instrumentation is a large subject; dynamic sql generation is something to be avoided if possible. Remember, Oracle is written with the idea that many people are going to be sharing code and the database, so it is optimized in that way. For SQL parsing in particular, if every SQL is different, you get a performance problem called "hard parsing." You can (and generally should, and sometimes can't avoid) use bind variables so that Oracle doesn't need to hard parse every SQL. In fact, this is one of those things that applies to other engines besides Oracle. I would recommend you read Tom Kyte's books, he explains what is going on in detail, including in some places the non-Oracle viewpoint.
>
Furthermore, Since the database is not a production database, it is there so I can do my tests. I don't have to be concerned with what other sessions may be doing to my system. There are only the sessions I control.No, there are sessions Oracle controls. If you are on unix, you can easily see this, but there are ways to see it on Windows, too. In some cases, your own sessions can affect themselves.
>
then what it the array fetch size ? If the array fetch size is large enough the number of block visits would be similar to the number of physical block reads.
I don't know what the arraysize you mention is. i have not touched that parameter. So whatever it is, it's the default.You should find out! You can go to http://tahiti.oracle.com and type array fetch size into the search box. You can also go to http://asktom.oracle.com and do the same thing, with some more interesting detail.
>
By the way, I don't get the query results into my client, the query results are dumped into a target output table.
So, if the arraysize has something to do with the number of rows that Oracle is returning the client in each step... I think it doesn't matter.You may hear this phrase a lot:
"It depends."
>
As for the query plan, If i am not mistaken you can't get get query plans for queries that are: create table as select.What?
JG@TTST> explain plan for create table jjj as select * from product_master;
Explained.
JG@TTST> select count(*) from plan_table;
COUNT(*)
 3
I can however commit the create table part and just call for the evalution of the Select part of the query; i believe it should be same.
"Optimizer" "Cost" "Cardinality" "Bytes" "Partition Start" "Partition Stop" "Partition Id" "ACCESS PREDICATES" "FILTER PREDICATES"
"SELECT STATEMENT" "ALL_ROWS" "2563" "586110" "15238860" "" "" "" "" ""
"UNION-ALL" "" "" "" "" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "512" "117222" "3047772" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "513" "117222" "3047772" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "513" "117222" "3047772" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "513" "117222" "3047772" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "513" "117222" "3047772" "" "" "" "" ""
This query plan was taken from sql developer, exported to txt, and the PROFILE table here has only 100k tuples.
Right now I am more concerned with testing the MODEL query. Which Oracle doesn't seem to be able any more... but that is a matter for another thread.
Regarding this plan. The Union ALL seems to be more than just a binary Operator... IT seems to be Neray.
The union all on that execution plan seems to be taking as leaf tables 5 99sono.Profile tables, and be making a table scan to them all. So I'd say that the RDBMS should only scan each database block once and not 5 times.
But: It doesn't seem to be so. IT seems like what oracle is doing is scanning completly each the table, and then moving on to next select statement in the UNION ALL. Because given the amount of source table that was read, 5 times greater than the size of the source table. Oracle didn't reuse read blocks.
But this is just my feeling.Your feeling is uninteresting. Telling us what you really hope to accomplish might be more interesting.
Anyway, in terms of consistent gets, how many consistent gets should the RDBMS be doing? 5
One for each table block?It depends.
>
My best regards,
Nuno (99sono xp).

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Pctfree=0-table high free blockspace ratio?

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