Re: Setting for db_block_buffer v.s. db_block_size

ou're going way off the deep end with this one. db_block_buffers is the NUMBER of buffers, each sized as per db_block_size, that you want held in the Instance (ie, in memory).

In other words, with a 4K block size, if you set _buffers to 1000, you'll be cacheing 4MB of data in memory. If you set _block_buffers to 20000, you'll be cacheing 80MB in memory.

Generally, the more data you can cache, the less visits to (slow) hard disk you have to perform to retrieve data, therefore performance improves. Don't overdo it, though: cacheing data that no-one really wants is a waste of memory. And if you make your cache too big, you'll induce the operating system itself to start swapping out to its paging file... meaning visits to disk, therefore slow performance.

Getting precisely the right size for db_block_buffers can be tricky, and is what database tuning is all about. But with a 4K block size, I'd set block_buffers to about 20000 to start with: 80MB is not huge, but it's usefully large. After that, it's time to start tuning.

Regards
HJR "robert" <newsreply@#removethis#cookiesoftware.nl> wrote in message news:apmpcn$19r$1_at_reader15.wxs.nl...
> Hello,
>
> I have a question about db_block_size and db_block_buffer
>
> I have set the db_block_size the same as the disks (4096)
> I am not sure what the settings for db_block_buffer should be ?
>
> That probably because i don't exactly know what block_buffer does.
> Is the the amount of bits kept in RAM ? In that case i can imagine that i
> should
> keep the block_buffer the same or at least bigger than block_size. To read
> 1/2 a block into RAM the OS
> still has to read 1 entire block. Reading a total block into RAM halves my
> reading (not exactly...)
>
>
> Cheers,
>
> Robert
>
>
>
>
>
Received on Tue Oct 29 2002 - 14:18:30 CST