Re: Inconsistent multi-block io

On Jul 7, 4:19 pm, mak..._at_gmail.com wrote:
> I'm on 10gR2 on AIX with ASM. have DB_FILE_MULTIBLOCK_READ_COUNT=16 in
> spfile. but still see different block size for "db file scattered
> read" ranging from 2 to 16. Can someone explain why its ranging from
> 2-16? Shouldn't DBRC always be followed if it's set in SPFILE?
>
> see below excerpts from 10046 trace file.
>
> WAIT #3: nam='db file scattered read' ela= 48396 file#=61 block#=416
> blocks=5 obj#=80135 tim=1526895870393
> WAIT #3: nam='db file scattered read' ela= 8210 file#=61 block#=33717
> blocks=4 obj#=80135 tim=1526895880210
> WAIT #3: nam='db file scattered read' ela= 7306 file#=61 block#=52614
> blocks=3 obj#=80135 tim=1526895897691
> WAIT #3: nam='db file scattered read' ela= 8508 file#=61 block#=53030
> blocks=16 obj#=80135 tim=1526896239141
> WAIT #3: nam='db file scattered read' ela= 15903 file#=61 block#=53046
> blocks=15 obj#=80135 tim=1526896258427
> WAIT #3: nam='db file scattered read' ela= 921 file#=61 block#=53379
> blocks=2 obj#=80135 tim=1526896507844
>
> Thanks

It is being followed, as it's the MAXIMUM number of blocks to be read in a single I/O operation, not the ONLY number of blocks to be read. So it should read what it needs to get the data, even if that's less than db_file_multiblock_read_count, but it will never read MORE than that number of blocks, and you have shown nothing which disproves that.

There's no problem here.

David Fitzjarrell Received on Tue Jul 08 2008 - 09:50:47 CDT