This is one of the most exciting new features for the DBA, especially now a day there are many databases where you can hardly distinguish between OLTP and DSS….
In the pre-9i releases, you define the BLOCK_SIZE when creating the database and it cannot be changed. In 9i also this is true. In addition to the standard block size of the database, you can create tablespaces with different block size. The block size of the tablespace is specified using the BLOCK SIZE clause of CREATE TABLESPACE.
For you to use this feature, you need to set the right buffer cache parameter. The DB_CACHE_SIZE specifies the buffer cache size for the objects in tablespaces created with the standard block size. DB_nK_CACHE_SIZE parameter sets the appropriate buffer cache for the non-standard block sized tablespace. ‘n’ could be 2, 4, 8, 16 or 32 but it should not be equal to your standard block size. The default values for DB_nK_CACHE_SIZE parameters are 0.
- SQL> show parameter db%cache
-
- NAME TYPE VALUE
- ------------------------------------ ----------- -------
- db_16k_cache_size big integer 0
- db_2k_cache_size big integer 0
- db_32k_cache_size big integer 0
- db_4k_cache_size big integer 0
- db_8k_cache_size big integer 0
- db_cache_advice string OFF
- db_cache_size big integer 0
- db_keep_cache_size big integer 0
- db_recycle_cache_size big integer 0
- SQL> show parameter db_block
-
- NAME TYPE VALUE
- ------------------------------------ ----------- -------
- db_block_buffers integer 1500
- db_block_checking boolean FALSE
- db_block_checksum boolean TRUE
- db_block_size integer 8192
- SQL>
Look at the above parameters; since the database was upgraded from 8i, it is still using the old style buffer cache sizing using DB_BLOCK_BUFFERS. Here we cannot set any of the DB_nK_CACHE_SIZE parameter because you have not used the DB_CACHE_SIZE parameter to start the database.
- SQL> alter system set db_4k_cache_size=20;
- alter system set db_4k_cache_size=20
- *
- ERROR at line 1:
- ORA-02097: parameter cannot be modified because specified value is invalid
- ORA-00381: cannot use both new and old parameters for buffer cache size
- specification
-
- SQL>
Let’s try another database:
- SQL> show parameter db%cache
-
- NAME TYPE VALUE
- ------------------------------------ ----------- ------------
- db_16k_cache_size big integer 0
- db_2k_cache_size big integer 0
- db_32k_cache_size big integer 0
- db_4k_cache_size big integer 0
- db_8k_cache_size big integer 0
- db_cache_advice string ON
- db_cache_size big integer 83886080
- db_keep_cache_size big integer 0
- db_recycle_cache_size big integer 0
- SQL> show parameter sga
-
- NAME TYPE VALUE
- ------------------------------------ ----------- ------------
- lock_sga boolean FALSE
- pre_page_sga boolean FALSE
- sga_max_size big integer 220163984
- SQL>
- SQL> alter system set db_cache_size=20m;
-
- System altered.
-
- SQL> alter system set db_4k_cache_size=2M;
-
- System altered.
-
- SQL> show parameter db%cache
-
- NAME TYPE VALUE
- ------------------------------------ ----------- -------------------
- db_16k_cache_size big integer 0
- db_2k_cache_size big integer 0
- db_32k_cache_size big integer 0
- db_4k_cache_size big integer 16777216
- db_8k_cache_size big integer 0
- db_cache_advice string ON
- db_cache_size big integer 33554432
- db_keep_cache_size big integer 0
- db_recycle_cache_size big integer 0
- SQL>
- SQL>
- SQL> create tablespace test_biju datafile
- 2 '/ora_backup/test_biju.dbf' size 50m
- 3 extent management local
- 4* blocksize 4k
- SQL> /
-
- Tablespace created.
-
- SQL>
- SQL> select block_size from dba_tablespaces
- 2 where tablespace_name = 'TEST_BIJU';
-
- BLOCK_SIZE
- ----------
- 4096
-
- 1 row selected.
-
- SQL> drop tablespace test_biju including contents and datafiles;
-
- Tablespace dropped.
-
- SQL>
| 网站地图 |