Użytkownik Matthias Hoys napisał:
> Hi,
>
> What would be the recommended value for db_file_multiblock_read_count for an
> OLTP database (10g) on AIX 5.2 with JFS2 (and disk devices on SAN) ?
>
> I did some benchmarks with Oracle 8.1.7 (dfmrc set to 8,16,32 and 64) but
> couldn't find any significant performance differences when executing full
> table or index scans (and yes I bounced the db before each test).
>
> Is tuning this parameter still useful for Oracle 10g ?
>
>
> Matthias
>
>
Hello !
Tuning this parameter is always good idea, but it is connected with full
scans only ( blocks belonging to indexes are read only in 1-block reads )
Whats more - correct value of this parameter is dependend on
db_block_size value - more precisely :
if You want to get maximum performance benefits from this parameter set
it to value for which the following formula will be correct :
db_block_size * db_file_multiblock_read_count = maximum_1_read_size,
where maximum_1_read_size is the maximum of bytes which 1 call to system
function read can read from file system. For most sensible ;-) OS it is
equal to 64KB, but please check its value for Your platform in
documentation. Small benefits of setting this parameter in Your
benchmarks could be caused by large block size. But always better idea
is to set large block size - especially for indexes - it makes indexes
b-trees shorter and thus faster to read. Of course for an OLTP system
You should consider using large blocks for large amount of saimultaneous
transactions - so answer for question "how large blocks" is not simple.
Sorry for long answer, but i hope it helped You :-)
regards
Witek Swierzy
wswier_at_sgh.waw.pl
Received on Sun Jul 03 2005 - 16:36:54 CDT
