How does Oracle set the High Water Mark?

From: Feighery Raymond <Raymond.Feighery_at_churchill.com>
Date: Wed, 10 Mar 2004 13:56:27 -0000
Message-ID: <817D2444710B934B9F7B8A1DAAF432D601F2ADD4@brcexm03>

Oracle 9.2.0.4 Solaris 8

How does Oracle set the HWM? In the example below, I create a table and insert one row. I would expect only one block to be used, instead Oracle seems to have pushed the HWM up to 13 blocks. I can imagine that this might be done to "pre-mark" rows as used during bulk inserts, but how does Oracle decide where to set the HWM?

SQL> select * from dba_tablespaces where tablespace_name = 'EXAMPLE'; TABLESPACE_NAME BLOCK_SIZE INITIAL_EXTENT NEXT_EXTENT MIN_EXTENTS

------------------------------ ---------- -------------- -----------

MAX_EXTENTS PCT_INCREASE MIN_EXTLEN STATUS CONTENTS LOGGING FOR EXTENT_MAN ----------- ------------ ---------- --------- --------- --------- ---

ALLOCATIO PLU SEGMEN DEF_TAB_
--------- --- ------ --------
EXAMPLE 4096 65536 1
2147483645 65536 ONLINE PERMANENT LOGGING NO LOCAL SYSTEM NO AUTO DISABLED SQL> create table t (col1 number(1));
Table created.
SQL> analyze table t compute statistics; Table analyzed.
SQL> insert into t values(1);
1 row created.
SQL> commit;
Commit complete.
SQL> select blocks, empty_blocks from user_tables where table_name = 'T'; BLOCKS EMPTY_BLOCKS
---------- ------------

0 16
SQL> analyze table t compute statistics; Table analyzed.
SQL> select blocks, empty_blocks from user_tables where table_name = 'T'; BLOCKS EMPTY_BLOCKS
---------- ------------

13 3

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Received on Wed Mar 10 2004 - 07:56:48 CST