Re: VxFS Block Size

Hi Slava,

The memory page size is not necessarily invariant. For example, NT has a 4K memory page size on the Intel platform, but an 8K memory page size on Alpha. Did you check your page size with getconf?

Anyway, there is not normally any potential memory wastage on any platform if the database block is smaller than the memory page size. The one exception would be if you were to set the hidden _db_block_cache_protect parameter. If so, each buffer in db_block_buffers will be aligned to a memory protection unit boundary (normally one page) and so some memory may be left vacant. However, if you are silly enough to set that parameter, then the memory wastage would be a minor worry by comparison with the CPU overhead! So, no, the memory page size is not directly an issue when choosing a database block size.

@ Regards,
@ Steve Adams
@ http://www.ixora.com.au/
@ http://www.christianity.net.au/

-----Original Message-----
From: Viacheslav Leichinsky <v_leichinsky_at_ittoolbox.com>

Hello Steve,

I'll try to change my question. Is there sense to make db_block_size less than memory_page_size, e.g. db_block_size=2K and memory_page_size=4K under NT or db_block_size=8K and memory_page_size=16K under Relaint UNIX (as I know these memory page sizes are constant). Of course, such memory page size does not constrain the size of I/O operations but I concern about possible 50 % memory wastage because of db_block_size=1/2 of memory_page_size in these cases. Or Oracle works with memory itself without taking OS memory page size into consideration ?

Regards,
Slava. Received on Tue Oct 31 2000 - 05:25:38 CST