Memory Structures - Expert Oracle Database Architecture - page 159

■ If you've been following along, running the examples in your database, take this opportunity to log out of the
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Note

Multiple Block Sizes
Starting in Oracle9 i , you can have multiple database block sizes in the same database. Previously, all blocks in a single
database were the same size and in order to have a different block size, you had to rebuild the entire database. Now
you can have a mixture of the “default” block size (the block size you used when you initially created the database; the
size that is used for the SYSTEM and all TEMPORARY tablespaces) and up to four other block sizes. Each unique block size
must have its own buffer cache area. The default, keep, and recycle pools will only cache blocks of the default size.
In order to have a nondefault block size in your database, you need to have configured a buffer pool to hold them.
In this example, my default block size is 8KB. I will attempt to create a tablespace with a 16KB block size:

EODA@ORA12CR1> create tablespace ts_16k
2 datafile '/tmp/ts_16k.dbf'
3 size 5m
4 blocksize 16k;
create tablespace ts_16k
*
ERROR at line 1:
ORA-29339: tablespace block size 16384 does not match configured block sizes

EODA@ORA12CR1> show parameter 16k

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_16k_cache_size big integer 0

Right now, since I have not configured a 16KB cache, I can't create such a tablespace. I could do one of a couple
of things right now to rectify this situation. I could set the DB_16K_CACHE_SIZE parameter and restart the database. I
could shrink one of my other SGA components in order to make room for a 16KB cache in the existing SGA. Or,
I might be able to just allocate a 16KB cache if the SGA_MAX_SIZE parameter was larger than my current SGA size.

■ Starting in Oracle9 i , you can resize various SGa components while the database is up and running. If you want
to be able to “grow” the size of the SGa beyond its initial allocation, you must have set the SGA_MAX_SIZE parameter to
some value larger than the allocated SGa. For example, if after startup your SGa size was 800MB and you wanted to
add an additional 200MB to the buffer cache, you would have had to set the SGA_MAX_SIZE to 1GB or larger to allow for
the growth.

Note