On Mar 10, 2005, at 11:20 AM, Bob O'Neill wrote:
Hello. I am wondering why some of my queries are slow on the first run, but
speedy on subsequent runs. They are not being query cached, as I have
query_cache_type set to DEMAND. Is it something as simple as pulling the
data into RAM from disk, or is there something else going on? Here's a
simple example:
mysql> select count(*) from foo; +----------+ | count(*) | +----------+ | 1374817 | +----------+ 1 row in set (3.60 sec)
A table scan.
mysql> select count(*) from foo; +----------+ | count(*) | +----------+ | 1374817 | +----------+ 1 row in set (0.92 sec)
Another table scan, but now some or all of the table is cached in RAM (disk cache) by the OS (not by MySQL).
mysql> show variables like 'query_cache_type'; +------------------+--------+ | Variable_name | Value | +------------------+--------+ | query_cache_type | DEMAND | +------------------+--------+ 1 row in set (0.00 sec)
You could probably verify that the query cache wasn't used by monitoring the query cache stats <http://dev.mysql.com/doc/mysql/en/query-cache-status-and- maintenance.html>.
I am running MySQL 4.1.10 with InnoDB on RHEL 2.1 (kernel
2.4.9-e.49enterprise). Binaries are Linux x86 glibc static gcc RPMs from
mysql.com.
Thanks, -Bob
Michael
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