Re: why CPU is high while disks are idle in a table scan???

[Brent Baisley]

If all your queries are on columns that are indexed (query by key), 
then all your data for your query may actually fit into cache. If you 
are only pulling data from a "key" field, then MySQL doesn't need to 
actually access the whole table, just the index.
You usually see high disk usage when you are accessing a lot of data, 
which is not necessarily the same as accessing a lot of rows.

On Jun 21, 2004, at 12:57 PM, Leonardo Francalanci wrote:
I'm doing some tests on a 16.000.000 rows table.
Doing a simple "SELECT SUM(MYFIELD) FROM MYTABLE" I noticed
that disks are at 0.1%, while cpu arrives up to 80%.
How is that possible? My HDs are IDE. MySql has around
30Mb of ram, I thought it should read a lot from disk.
Even doing lots of queries by key I get only high cpu usage,
not disk reads.
Is that normal?
--
Brent Baisley
Systems Architect
Landover Associates, Inc.
Search & Advisory Services for Advanced Technology Environments
p: 212.759.6400/800.759.0577
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