At 8:01 -0800 1/11/03, James M. Luedke wrote:
>Hello:
> I have a few questions about how MySQL uses Ram. I have a machine
>that I am using as a database server. The machine has close to 1G
>of ram. It is running Slackware Linux 8.1 With a 2.4.18 kernel.
>The main use of this server is a backend for Radius Authentication.
>
> I have read all of the documentation I have been able to get my
>hands on, and believe I have a very good understanding of how MySQL
>works in general. However, this has me a little stumped.
>
> Please take a look at the output from top, my.cnf, and the processlist
>below.
>
>-------begin top output-----------------
>top - 15:21:46 up 56 days, 10:57, 11 users, load average: 0.03, 0.16, 0.15
>Tasks: 61 total, 1 running, 58 sleeping, 2 stopped, 0 zombie
>Cpu(s): 5.6% user, 2.0% system, 0.0% nice, 92.5% idle
>Mem: 900472k total, 896048k used, 4424k free, 22956k buffers
>Swap: 907664k total, 3676k used, 903988k free, 744248k cached
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ Command
> 2361 mysql 9 0 53416 52m 2068 S 0.3 5.9 2:48.61
>mysqld
> 2357 mysql 9 0 53416 52m 2068 S 0.0 5.9 0:00.18
>mysqld
> 2359 mysql 9 0 53416 52m 2068 S 0.0 5.9 0:00.28
>mysqld
> 2360 mysql 9 0 53416 52m 2068 S 0.0 5.9 0:11.29
>mysqld
> 2362 mysql 9 0 53416 52m 2068 S 0.0 5.9 17:28.20
>mysqld
> 2371 mysql 9 0 53416 52m 2068 S 0.0 5.9 0:02.82
>mysqld
> 2386 mysql 9 0 53416 52m 2068 S 0.0 5.9 0:00.12
>mysqld
> 2395 mysql 9 0 53416 52m 2068 S 0.0 5.9 0:01.01
>mysqld
> 2419 mysql 9 0 53416 52m 2068 S 0.0 5.9 0:00.21
>mysqld
> 2427 mysql 9 0 53416 52m 2068 S 0.0 5.9 17:00.51
>mysqld
> 2428 mysql 9 0 53416 52m 2068 S 0.0 5.9 0:03.32
>mysqld
> 2458 mysql 9 0 53416 52m 2068 S 0.0 5.9 0:01.15
>mysqld
>-------end top output-----------------
>
>Notice that when viewing top output for user mysql that there are
>12 seprate processes? I am assuming that this is done for connections
No. Linux displays threads as processes. They're all the same process.
>that the MySQL server may need to field. Does MySQL spawn a new
>process for every connection that comes in? And if so why do I have
Spawns a new thread.
>12 processes when the output from show processlist returns 7 rows.
Administrative threads.
>Is this how you would expect the MySQL server to behave? It appears
>that MySQL is sucking up a large amount of system recourses even
>when no-one is connected... There is little else running on this
>system besides MySQL. I have read similar messages to this email
>in the mysql list archive, and am familiar with the fact that MySQL
>will use key_buffer amount of ram for the mysqld process. According
>to the top output It would appear to me that MySQL is using
>52M*12 of ram which is 624M. Am I correct in my understanding?
There's only one key_buffer (now called key_buffer_size), shared by
all threads.
Now, read_buffer_size and sort_buffer_size, that's a different
matter. :-)
>I would assume that MySQL would share the cache between processes.
>Is there a reason why each process needs key_buffer ram?
>Am I doing something horribly wrong?
Nope. You're simply thinking that there are more processes than
there really are.
>
>
>---------show processlist output -----
>+-----+-------------+----------------+------------+-------------+-------+---------------------------------------------+------------------+
>| Id | User | Host | db | Command |
>Time | State | Info
>|
>+-----+-------------+----------------+------------+-------------+-------+---------------------------------------------+------------------+
>| 1 | radiusd | localhost | radiusd_db | Sleep | 0
>| | NULL |
>| 20 | root | localhost | customers | Sleep |
>23750 | | NULL
>|
>| 49 | radiusd | 216.250.251.22 | radiusd_db | Sleep |
>23076 | | NULL
>|
>| 80 | root | localhost | customers | Sleep |
>22168 | | NULL
>|
>| 403 | radiusd | 64.139.37.2 | radiusd_db | Sleep | 2
>| | NULL |
>| 524 | replication | 64.139.37.2 | NULL | Binlog Dump |
>9218 | Slave connection: waiting for binlog update | NULL
>|
>| 769 | root | localhost | radiusd_db | Query | 0
>| NULL | show processlist |
>+-----+-------------+----------------+------------+-------------+-------+---------------------------------------------+------------------+
>-----end show processlist output -----
[clipped]
>
>Just a side question. I noticed in the show variables output the variable
>have_raid? I do have the data directory stored on an external raid device,
>however the variable is set to NO. Will this cause me any problems...
have_raid relates to the RAID_XXX table creation options.
