records_per_block: can be set when the table has a lot of data?

Hello

We have a partition table with a length of middle line of 7K, and there are a lot of the line string. The score is based on the date, old partition will be truncated and reused later. I'm trying to find a way to limit the rows by block 1 (pct_free is another way, but is not reliable), it looks like records_per_block is a parameter that could be defined at the table level. But unfortunately, my test shows that the use of records_per_block, the table must be an empty table and insert a row inside and then set records_per_block, otherwise records_per_block will be ignored. Is there a solution?
SQL> create table t_11 as select rownum a, rpad('x',100,'x') b from dual connect by rownum<100;
 
Table created
SQL> delete t_11 where a<65;
 
64 rows deleted
SQL> select dbms_rowid.rowid_block_number(rowid),count(*) from t_11 group by dbms_rowid.rowid_block_number(rowid);
 
DBMS_ROWID.ROWID_BLOCK_NUMBER(   COUNT(*)
------------------------------ ----------
                        121354          2
                        121355         33
SQL> alter table t_11 minimize records_per_block;
 
Table altered
SQL> select dbms_rowid.rowid_block_number(rowid),count(*) from t_11 group by dbms_rowid.rowid_block_number(rowid);
 
DBMS_ROWID.ROWID_BLOCK_NUMBER(   COUNT(*)
------------------------------ ----------
                        121354          2
                        121355         33
SQL> insert into t_11 select * from t_11 where rownum<100;
 
35 rows inserted
SQL> select dbms_rowid.rowid_block_number(rowid),count(*) from t_11 group by dbms_rowid.rowid_block_number(rowid);
 
DBMS_ROWID.ROWID_BLOCK_NUMBER(   COUNT(*)
------------------------------ ----------
                        121354         37
                        121355         33

A solution that is not quite perfect - alter table XXX pctfree, pctused 99 1.
Unless your beginning of lines off incredibly short it will probably limit you to one line per block for the future DML.

As a guideline for "ranks shortcuts" (and this may vary slightly depending on whether you use SAMS or not):

SQL> insert into t1 values(rpad('x',42));

1 row created.

SQL> insert into t1 values(rpad('x',1));

1 row created.

SQL> select rowid from t1;

ROWID
------------------
AAAY2bAAFAAAA4KAAA
AAAY2bAAFAAAA4LAAA

Your analysis of the rows_per_block is not quite right — but the critical point is correct, it is very difficult to get the recorded "records per block" reduced once you have data in place. Here is an improved version of your test cut-n-pasted from a SQL * Plus term in 10.2.0.3:

SQL> @temp
SQL> set echo on
SQL>
SQL> drop table t_11;

Table dropped.

SQL>
SQL> create table t_11 as select rownum a, rpad('x',100,'x') b from dual connect by rownum<100;

Table created.

SQL>
SQL> select dbms_rowid.rowid_block_number(rowid),count(*) from t_11 group by dbms_rowid.rowid_block_number(rowid);

DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)   COUNT(*)
------------------------------------ ----------
                                5642         66
                                5643         33

2 rows selected.

SQL>
SQL> delete t_11 where a between 31 and 70;

40 rows deleted.

SQL>
SQL> select dbms_rowid.rowid_block_number(rowid),count(*) from t_11 group by dbms_rowid.rowid_block_number(rowid);

DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)   COUNT(*)
------------------------------------ ----------
                                5642         30
                                5643         29

2 rows selected.

SQL>
SQL> alter table t_11 minimize records_per_block;

Table altered.

SQL>
SQL> select dbms_rowid.rowid_block_number(rowid),count(*) from t_11 group by dbms_rowid.rowid_block_number (rowid);

DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)   COUNT(*)
------------------------------------ ----------
                                5642         30
                                5643         29

2 rows selected.

SQL>
SQL> insert into t_11 select * from t_11 where rownum<100;

59 rows created.

SQL>
SQL> select dbms_rowid.rowid_block_number(rowid),count(*) from t_11 group by dbms_rowid.rowid_block_number(rowid);

DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)   COUNT(*)
------------------------------------ ----------
                                5644         33
                                5642         33
                                5643         33
                                5645         19

4 rows selected.

SQL> spool off

I delete the last lines 36 to one block and the first 4 lines on the other. For this reason, Oracle is capable (on the block drain plug) to reduce the size of the + 'line directory' + in the first block by removing the pointers 'empty' to the end of the book - but it cannot eliminate all entries in the directory of the line of the second block because the "empty" pointers are not at the end of the directory.

Code to determine the limit on the number of lines per block looks like the size of the largest directory online - not the current number of rows in the block.

In my example, the largest directory of line is 33 because the last 34 entries have been pruned at the end; in your example, the largest directory of line was still 67 because your deletion had left two rows at the end of the directory.

Concerning
Jonathan Lewis
http://jonathanlewis.WordPress.com
http://www.jlcomp.demon.co.UK

"Science is more than a body of knowledge; It's a way of thinking. "
Carl Sagan

Tags: Database

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