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
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 >
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.bergen@stripped> 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 <dnelson@stripped> 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.
>>> > then they never seem to take that long after the first time (taking
>>> > than a second then). If I change the "keywords" searched for in
>>> > 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
>> 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
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> Eric Bergen
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