Re: Multi-Block read count

hello Norman,

it is platform dependent. The method I use in order to determine the maximum in a database is simple, using sqlplus:
* alter session set db_file_multiblock_read_count = 10000;

• show parameters db_file_multiblock_read_count

On my NT laptop, with RDBMS 9.0.1, db_file_multiblock_read_count can be set to 64, so with 8 Kb block size, at most 512 Kbyte can be read.

On our Linux server (still linux 2.2, RDBMS 8.1.6), also with 8 Kb blocks, db_file_multiblock_read_count can be set to 128.

The largest figure I have seen was 512 with a block size of 8Kbyte, on SGI, RDBMS 7.3. We double-checked that one with wait-events set on, and truss/trace/strace (can't remember which one), and it really read 4 Mbyte per I/O.

Note that with full table/index/partition scans, extent boundaries are never crossed. Strange enough, physically contiguous extents are not coalesced.

Kind Regards,

Herman de Boer
sr. consultant
IT Consultancy Group bv Received on Wed Jan 09 2002 - 08:29:19 CST