Re: [gentoo-user] mysqld invoked oom-killer

[Albert Hopkins]

On Thursday, July 21 at 16:53 (-0700), Grant said:


> So swap isn't treated exactly like RAM.  It actually has special
> handling in Linux which makes it beneficial to have on almost any
> Linux system?  According to Alan, things get very bad when a Linux
> system hits swap.  How can behavior like this be beneficial:
>
> "When a linux machine hits swap, it does so very aggressively, there
> is nothing nice about it at all. The entire machine slows to a
> painstaking crawl for easily a minute at a time while the kernel
> writes pages out to disk, and disk is thousands of times slower than
> RAM.
>
This is not entirely true.  There's regular swapping and there is
"thrashing".  Thrashing is indicative of a memory-starved system, i.e.
when many processes are trying to access memory, but there just isn't
enough and the system is frantically swapping in/out.  I'm talking about
your normal day-to-day swapping that you probably don't even notice.

> It gets so bad that you can't even run a shell properly to try and see
> what's going on and kill the actual memory hog."

Again, that is thrashing.  I'm talking about "normal" swappage.  Dont
throw the baby out with the bath water.

> Also, aren't you likely to wear out your hard disk sooner using swap?

Is this coming from someone who uses Gentoo linux, which is constantly
downloading/compiling/linking object files?   Syslog and other loggers
writing everything under the sun to a log file.  Backups, journal
writes, database transactions, etc.  Compare how many disk transactions
take place during your normal Gentoo usage versus a few megabytes
here/there being swapped in/out.  Again, I'm talking about regular
swapping, not "oh my god I has no RAM and my hard drive won't stop"
Even so, we're talking about modern drives here.  This isn't the 1960s.