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OS read buffer size - I/O channel

Raj Patel_1
Occasional Advisor

OS read buffer size - I/O channel

How do I determine the OS read buffer size on an HPUX system? I have an 8k db_block_size and want to correctly determine the db_multi_block_read_count parameter.
Edward Sedgemore
Trusted Contributor

Re: OS read buffer size - I/O channel

If you have an 8k db block size in Oracle then you want to match this with the blocksize of the logical volume.
To find out what it is;

fstyp -v | grep bsize

The normal blocksize for JFS filesystems is 8k anyway.
Esteemed Contributor

Re: OS read buffer size - I/O channel

Hi Raj,

hfs block size is 8k and jfs is 1k , but may be this is not what you want :

following is topic about db_multi_block_read_count

It depends on what kind of application (DSS,OLTP) your database is running. Increasing DB_FILE_MULTIBLOCK_READ_COUNT doesnt always increase performance. Other factors like size of tables and whether parallel query is being utilized come into the picture. Unlike db_file_mult_read_cnt which is primarily for I/O performance, DB_BLOCK_SIZE affects other parameters like the maximum value of the 'freelists' storage param for tables and indexes. Increasing db_block_size also requires recreating your whole database with a larger block size. I dont think it's worthwhile to do that just for a small performance increase in I/O. So increasing one or the other is definitely not the same. I would increase the DB_file_mult... if I/O performace was an issue and test the results first.
this is from oracle metalink

why not start at 16 ?

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