Re: why CPU is high while disks are idle in a table scan???
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 -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/[EMAIL PROTECTED]
Re: why CPU is high while disks are idle in a table scan???
On Mon, Jun 21, 2004 at 06:57:51PM +0200, 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? Hard to say, but in a table scan the CPU does have a lot of work to do. It needs to do about 16,000,000 comparisons (based on your info). Jeremy -- Jeremy D. Zawodny | Perl, Web, MySQL, Linux Magazine, Yahoo! <[EMAIL PROTECTED]> | http://jeremy.zawodny.com/ [book] High Performance MySQL -- http://highperformancemysql.com/ -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/[EMAIL PROTECTED]
