Emptying the buffers cache

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Emptying the buffers cache

If you ever want to empty it can use this chain of commands.

# free && sync && echo 3 > /proc/sys/vm/drop_caches && free             total       used       free     shared    buffers     cachedMem:       1018916     980832      38084          0      46924     355764-/+ buffers/cache:     578144     440772Swap:      2064376        128    2064248             total       used       free     shared    buffers     cachedMem:       1018916     685008     333908          0        224     108252-/+ buffers/cache:     576532     442384Swap:      2064376        128    2064248

You can signal the Linux Kernel to drop various aspects of cached items by changing the numeric argument to the above comm and.

• To free Pagecache:

  # echo 1 > /proc/sys/vm/drop_caches

• To free dentries and inodes:

  # echo 2 > /proc/sys/vm/drop_caches

• To free Pagecache, dentries and Inodes:

  # echo 3 > /proc/sys/vm/drop_caches

The above is meant to be run as root. If you ' re trying to do them using and you'll need to change the sudo syntax slightly to something like these:

$ sudo sh -c ‘echo 1 >/proc/sys/vm/drop_caches‘$ sudo sh -c ‘echo 2 >/proc/sys/vm/drop_caches‘$ sudo sh -c ‘echo 3 >/proc/sys/vm/drop_caches‘

Note: There's a more esoteric version of the above command if you ' re to that:

$ echo "echo 1 > /proc/sys/vm/drop_caches" | sudo sh

Why the syntax? The program /bin/echo is running as root, because sudo of, and the shell that ' s redirecting Echo's output to the Root-only file is still running as you. Your current Shell Does the redirection before sudo starts.

Seeing ' s in the buffers and cache

Take a look at if your ' d like to analyze the contents of the linux-ftools buffers & cache. Specifically if you ' d like to see what files is currently being cached.

Fincore

With this tool you can see what files is being cached within a give directory.

fincore [options] files...  --pages=false      Do not print pages  --summarize        When comparing multiple files, print a summary report  --only-cached      Only print stats for files that are actually in cache.

For example, /var/lib/mysql/blogindex :

[email protected]:/var/lib/mysql/blogindex# fincore--pages=false--summarize--only-cached * stats for CLUSTER_  LOG_2010_05_21.MYI:file size=93840384, Total pages=22910, cached Pages=1, cached size=4096, cached perc=0.004365 stats For CLUSTER_LOG_2010_05_22.MYI:file size=417792, total pages=102, cached Pages=1, cached size=4096, cached perc=0.980 392 stats for CLUSTER_LOG_2010_05_23.MYI:file size=826368, total pages=201, cached Pages=1, cached size=4096, cached p erc=0.497512 stats for CLUSTER_LOG_2010_05_24.MYI:file size=192512, total pages=47, cached Pages=1, cached size=4096, Cached perc=2.127660 stats for CLUSTER_LOG_2010_06_03.MYI:file size=345088, total pages=84, cached pages=43, cached Si ze=176128, cached perc=51.190476 stats for CLUSTER_LOG_2010_06_04.MYD:file size=1478552, total pages=360, cached pages= Cached size=397312, cached perc=26.944444 stats for CLUSTER_LOG_2010_06_04.MYI:file size=205824, Total pages=50, C ached pages=29, Cached size=118784, cached perc=58.000000 stats for COMMENT_CONTENT_2010_06_03.MYI:file size=100051968, Total pages=24426, cached p ages=10253, cached size=41996288, cached perc=41.975764 stats for COMMENT_CONTENT_2010_06_04.MYD:file size=716369644, t Otal pages=174894, Cached pages=79821, cached size=326946816, cached perc=45.639645 stats for comment_content_2010_06_04 . Myi:file size=56832000, Total pages=13875, cached pages=5365, cached size=21975040, cached perc=38.666667 stats for FE ED_CONTENT_2010_06_03.MYI:file size=1001518080, Total pages=244511, cached pages=98975, cached size=405401600, Cached perc=40.478751 stats for FEED_CONTENT_2010_06_04.MYD:file size=9206385684, total pages=2247652, cached pages=1018661, Cached size=4172435456, cached perc=45.321117 stats for FEED_CONTENT_2010_06_04.MYI:file size=638005248, Total pages=15 5763, cached pages=52912, cached size=216727552, cached perc=33.969556 stats for FEED_CONTENT_2010_06_04.frm:file size= 9840, Total pages=2, Cached pages=3, Cached size=12288, cached perc=150.000000 stats for PERMALINK_CONTENT_2010_06_03.MYI:file size=103529062 4, total pages=252756, cached pages=108563, cached size=444674048, cached perc=42.951700 stats for permalink_content_20 10_06_04.myd:file size=55619712720, Total pages=13579031, cached pages=6590322, cached size=26993958912, cached perc=4 8.533080 stats for PERMALINK_CONTENT_2010_06_04.MYI:file size=659397632, total pages=160985, cached pages=54304, cache D size=222429184, cached perc=33.732335 stats for PERMALINK_CONTENT_2010_06_04.frm:file size=10156, Total pages=2, Cach Ed pages=3, Cached size=12288, cached perc=150.000000---total cached size:32847278080

With the above output you can see that there is several *. MYD, *. MYI, and *.frm files that is currently being cached.

Swap

If you want to clear out your swap you can use the following commands.

$ free             total       used       free     shared    buffers     cachedMem:       7987492    7298164     689328          0      30416     457936-/+ buffers/cache:    6809812    1177680Swap:      5963772     609452    5354320

Then use the This command to disable swap:

$ swapoff -a

Can confirm that it's now empty:

$ free             total       used       free     shared    buffers     cachedMem:       7987492    7777912     209580          0      39332     489864-/+ buffers/cache:    7248716     738776Swap:            0          0          0

and to re-enable it:

$ swapon -a

And now reconfirm with free :

$ free             total       used       free     shared    buffers     cachedMem:       7987492    7785572     201920          0      41556     491508-/+ buffers/cache:    7252508     734984Swap:      5963772          0    5963772

Emptying the buffers cache