About having a large SGA for a DataWarehouse
- From: Hemant K Chitale <hkchital@xxxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Mon, 19 Jul 2004 20:32:23 +0800
At my site we'll be migrating a [currently very small 20GB] Corporate
DataWarehouse
from 32-bit 8.1.7 Solaris to 32-bit 9i Linux. It will grow rapidly with
Manufacturing Datamarts
to probably 500GB in a year.
Some of the DataMart teams are pushing for a very large SGA while I would
rather have a
large PGA_AGGREGATE_TARGET [not using 10g and Automatic Memory Management]
My rebuttal was :
We must consider how large we really need the SGA. A too large SGA
[assuming that it is not too large as to cause excessive Paging and begin
Swapping at the OS level]
can result in :
a. Performance impact in Checkpoints -- larger checkpoints, longer
write times for DBWR
b. Performance impact in Free Buffer scans -- longer buffer chains
c. Performance impact on Cache Buffer Chains latch -- more buffers per
latch means that the latch may be held more frequently
d. Delayed Block Cleanouts -- modified blocks remaining in memory
requiring cleanups and causing potential ORA-1555s
Comments / Recommendations / Corrections from this list, please ?
Hemant K Chitale
Oracle 9i Database Administrator Certified Professional
http://web.singnet.com.sg/~hkchital
"A man's reputation is what other people think of him; his character is
what he really is."
-- Miner, Jack
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