Journal Block Size
The alterdb command specifies the journal block size in the format:
alterdb dbname -jnl_block_size=n
Only one database name is required. Valid journal block sizes are 4096, 8192, 16384, 32768, and 65536 bytes.
Archiver (dmfacp) performance is affected by the journal file block size. You normally change the block size (Size edit control) in conjunction with the number of target journal blocks (-target_jnl_blocks). Doing so allows you to target the creation of journal files of a given size. Changing the block size without also changing the number of blocks in a journal file changes the target size of the file.
You typically change the journal block size immediately after the database is created, before the initial checkpoint is taken with the journaling option. Thereafter, changing the journal block size is generally required only for installations with a relatively high volume of journaled data. You can only change the journal block size when journaling is not currently enabled.
To change the journal block size on a database that is currently journaled
1. Take a checkpoint and disable journaling:
ckpdb -j dbname
2. Set the journal block size:
alterdb dbname -jnl_block_size=n
3. Take a checkpoint and enable journaling:
ckpdb +j dbname
When this operation completes successfully, a message is written to the errlog.log. The updated journal file block size can be observed as the infodb “Journal block size” parameter.