How does Oracle set the High Water Mark?
- From: Feighery Raymond <Raymond.Feighery@xxxxxxxxxxxxx>
- To: "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 10 Mar 2004 13:56:27 -0000
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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