Non Standard Block Size

Oracle9i New Feature Series: Using Multiple Block Sizes in a Database 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 -----------------------------------db_16k_cache_size db_2k_cache_size db_32k_cache_size db_4k_cache_size db_8k_cache_size

db_cache_advice

TYPE ----------big integer big integer big integer big integer big integer

VALUE ------0 0 0 0 0

string

db_cache_size db_keep_cache_size db_recycle_cache_size SQL> show parameter db_block

big integer 0 big integer 0 big integer 0

NAME -----------------------------------db_block_buffers db_block_checking db_block_checksum db_block_size SQL>

TYPE ----------integer boolean boolean integer

OFF

VALUE ------1500 FALSE TRUE 8192

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 -----------------------------------db_16k_cache_size db_2k_cache_size db_32k_cache_size db_4k_cache_size db_8k_cache_size db_cache_advice db_cache_size db_keep_cache_size db_recycle_cache_size SQL> show parameter sga

TYPE ----------big integer big integer big integer big integer big integer string big integer big integer big integer

VALUE -----------0 0 0 0 0 ON 83886080 0 0

NAME TYPE ------------------------------------ ----------lock_sga boolean pre_page_sga boolean sga_max_size big integer SQL> SQL> alter system set db_cache_size=20m;

VALUE -----------FALSE FALSE 220163984

System altered. SQL> alter system set db_4k_cache_size=2M; System altered. SQL> show parameter db%cache NAME TYPE ------------------------------------ ----------db_16k_cache_size big integer db_2k_cache_size big integer db_32k_cache_size big integer db_4k_cache_size big integer db_8k_cache_size big integer db_cache_advice string db_cache_size big integer db_keep_cache_size big integer db_recycle_cache_size big integer 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.

VALUE ------------------0 0 0 16777216 0 ON 33554432 0 0

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>