I had heard of that trick but never looked it up. 'man proc' tells me
/proc/sys/vm/drop_caches (since Linux 2.6.16)
Writing to this file causes the kernel to drop clean caches,
dentries and inodes from memory, causing that memory to become
free.
To free pagecache, use echo 1 > /proc/sys/vm/drop_caches; to
free dentries and inodes, use echo 2 > /proc/sys/vm/drop_caches;
to free pagecache, dentries and inodes, use echo 3 >
/proc/sys/vm/drop_caches.
Because this is a non-destructive operation and dirty objects
are not freeable, the user should run sync(8) first.
I should read the whole man page...
On Fri, May 29, 2009 at 5:59 PM, Eric Bergen <eric.ber...@gmail.com> wrote:
> You can also flush the cache with echo 1 > /proc/sys/vm/drop_caches if
> you have a new enough kernel.
>
> On Fri, May 29, 2009 at 2:16 PM, Dan Nelson <dnel...@allantgroup.com> wrote:
>> In the last episode (May 29), Gerald L. Clark said:
>>> Little, Timothy wrote:
>>> > Also titled, I want this to run slow ALL the time...
>>> >
>>> > I have a group of dreadful queries that I have to optimize.
>>> >
>>> > Some take 20-30 seconds each -- the first time that I run them. But
>>> > then they never seem to take that long after the first time (taking less
>>> > than a second then). If I change the "keywords" searched for in the
>>> > where clauses, then they take a long time again... so it's the
>>> > query-cache or something just like it.
>>> >
>>> > BUT, I am doing this each time :
>>> > flush tables;
>>> > reset query cache;
>>> > set global query_cache_size=0;
>>> > SELECT SQL_NO_CACHE DISTINCT ca.conceptid AS headingid,
>>> >
>>> > And still it's not avoiding the cache.
>>> >
>>> > Is there a cache I'm missing?
>>> >
>>> > Tim...
>>> >
>>> >
>>> Disk cache, but I don't know how to clear it.
>>
>> Create a file 2x the size of your RAM (for a 2gb system, dd if=/dev/zero
>> of=bigfile bs=1024k count=4096), then dd it to /dev/null (dd if=bigfile
>> of=/dev/null bs=1024k). That should flush your OS cache. The guaranteed
>> way would be to dismount then remount your filesystem, but that could be
>> difficult depending on how many other processes are using it..
>>
>> --
>> Dan Nelson
>> dnel...@allantgroup.com
>>
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>>
>
>
>
> --
> Eric Bergen
> eric.ber...@gmail.com
> http://www.ebergen.net
>
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