Emptying the buffers cache
\nIf you ever want to empty it you can use this chain of commands.<\/p>\n
$ free && sync && echo 3 > \/proc\/sys\/vm\/drop_caches && free<\/p>\n
total used free shared buffers cached
\nMem: 1018916 980832 38084 0 46924 355764
\n-\/+ buffers\/cache: 578144 440772
\nSwap: 2064376 128 2064248
\n total used free shared buffers cached
\nMem: 1018916 685008 333908 0 224 108252
\n-\/+ buffers\/cache: 576532 442384
\nSwap: 2064376 128 2064248
\nYou can signal the Linux Kernel to drop various aspects of cached items by changing the numeric argument to the above command.<\/p>\n
To free pagecache:
\n$ echo 1 > \/proc\/sys\/vm\/drop_caches
\nTo free dentries and inodes:
\n$ echo 2 > \/proc\/sys\/vm\/drop_caches
\nTo free pagecache, dentries and inodes:
\n$ echo 3 > \/proc\/sys\/vm\/drop_caches
\nThe above are meant to be run as root. If you\u2019re trying to do them using sudo then you\u2019ll need to change the syntax slightly to something like these:<\/p>\n
$ sudo sh -c ‘echo 1 >\/proc\/sys\/vm\/drop_caches’
\n$ sudo sh -c ‘echo 2 >\/proc\/sys\/vm\/drop_caches’
\n$ sudo sh -c ‘echo 3 >\/proc\/sys\/vm\/drop_caches’
\nNOTE: There\u2019s a more esoteric version of the above command if you\u2019re into that:<\/p>\n
$ echo “echo 1 > \/proc\/sys\/vm\/drop_caches” | sudo sh
\nWhy the change in syntax? The \/bin\/echo program is running as root, because of sudo, but the shell that\u2019s redirecting echo\u2019s output to the root-only file is still running as you. Your current shell does the redirection before sudo starts.<\/p>\n
Seeing what\u2019s in the buffers and cache
\nTake a look at linux-ftools if you\u2019d like to analyze the contents of the buffers & cache. Specifically if you\u2019d like to see what files are currently being cached.<\/p>\n
fincore
\nWith this tool you can see what files are being cached within a give directory.<\/p>\n
fincore [options] files…<\/p>\n
–pages=false Do not print pages
\n –summarize When comparing multiple files, print a summary report
\n –only-cached Only print stats for files that are actually in cache.
\nFor example, \/var\/lib\/mysql\/blogindex:<\/p>\n
root@xxxxxx:\/var\/lib\/mysql\/blogindex# fincore –pages=false –summarize –only-cached *
\nstats for CLUSTER_LOG_2010_05_21.MYI: file size=93840384 , total pages=22910 , cached pages=1 , cached size=4096, cached perc=0.004365
\nstats for CLUSTER_LOG_2010_05_22.MYI: file size=417792 , total pages=102 , cached pages=1 , cached size=4096, cached perc=0.980392
\nstats for CLUSTER_LOG_2010_05_23.MYI: file size=826368 , total pages=201 , cached pages=1 , cached size=4096, cached perc=0.497512
\nstats for CLUSTER_LOG_2010_05_24.MYI: file size=192512 , total pages=47 , cached pages=1 , cached size=4096, cached perc=2.127660
\nstats for CLUSTER_LOG_2010_06_03.MYI: file size=345088 , total pages=84 , cached pages=43 , cached size=176128, cached perc=51.190476
\nstats for CLUSTER_LOG_2010_06_04.MYD: file size=1478552 , total pages=360 , cached pages=97 , cached size=397312, cached perc=26.944444
\nstats for CLUSTER_LOG_2010_06_04.MYI: file size=205824 , total pages=50 , cached pages=29 , cached size=118784, cached perc=58.000000
\nstats for COMMENT_CONTENT_2010_06_03.MYI: file size=100051968 , total pages=24426 , cached pages=10253 , cached size=41996288, cached perc=41.975764
\nstats for COMMENT_CONTENT_2010_06_04.MYD: file size=716369644 , total pages=174894 , cached pages=79821 , cached size=326946816, cached perc=45.639645
\nstats for COMMENT_CONTENT_2010_06_04.MYI: file size=56832000 , total pages=13875 , cached pages=5365 , cached size=21975040, cached perc=38.666667
\nstats for FEED_CONTENT_2010_06_03.MYI: file size=1001518080 , total pages=244511 , cached pages=98975 , cached size=405401600, cached perc=40.478751
\nstats for FEED_CONTENT_2010_06_04.MYD: file size=9206385684 , total pages=2247652 , cached pages=1018661 , cached size=4172435456, cached perc=45.321117
\nstats for FEED_CONTENT_2010_06_04.MYI: file size=638005248 , total pages=155763 , cached pages=52912 , cached size=216727552, cached perc=33.969556
\nstats for FEED_CONTENT_2010_06_04.frm: file size=9840 , total pages=2 , cached pages=3 , cached size=12288, cached perc=150.000000
\nstats for PERMALINK_CONTENT_2010_06_03.MYI: file size=1035290624 , total pages=252756 , cached pages=108563 , cached size=444674048, cached perc=42.951700
\nstats for PERMALINK_CONTENT_2010_06_04.MYD: file size=55619712720 , total pages=13579031 , cached pages=6590322 , cached size=26993958912, cached perc=48.533080
\nstats for PERMALINK_CONTENT_2010_06_04.MYI: file size=659397632 , total pages=160985 , cached pages=54304 , cached size=222429184, cached perc=33.732335
\nstats for PERMALINK_CONTENT_2010_06_04.frm: file size=10156 , total pages=2 , cached pages=3 , cached size=12288, cached perc=150.000000
\n—
\ntotal cached size: 32847278080
\nWith the above output you can see that there are several *.MYD, *.MYI, and *.frm files that are currently being cached.<\/p>\n
Swap
\nIf you want to clear out your swap you can use the following commands.<\/p>\n
$ free
\n total used free shared buffers cached
\nMem: 7987492 7298164 689328 0 30416 457936
\n-\/+ buffers\/cache: 6809812 1177680
\nSwap: 5963772 609452 5354320
\nThen use this command to disable swap:<\/p>\n
$ swapoff -a
\nYou can confirm that it\u2019s now empty:<\/p>\n
$ free
\n total used free shared buffers cached
\nMem: 7987492 7777912 209580 0 39332 489864
\n-\/+ buffers\/cache: 7248716 738776
\nSwap: 0 0 0
\nAnd to re-enable it:<\/p>\n
$ swapon -a
\nAnd now reconfirm with free:<\/p>\n
$ free
\n total used free shared buffers cached
\nMem: 7987492 7785572 201920 0 41556 491508
\n-\/+ buffers\/cache: 7252508 734984
\nSwap: 5963772 0 5963772<\/p>\n","protected":false},"excerpt":{"rendered":"
Emptying the buffers cache If you ever want to empty it you can use this chain of commands.<\/p>\n
$ free && sync && echo 3 > \/proc\/sys\/vm\/drop_caches && free<\/p>\n
total used free shared buffers cached Mem: 1018916 980832 38084 0 46924 355764 -\/+ buffers\/cache: 578144 440772 Swap: 2064376 128 2064248 total used free shared […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"_links":{"self":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/5985"}],"collection":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5985"}],"version-history":[{"count":1,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/5985\/revisions"}],"predecessor-version":[{"id":5986,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/5985\/revisions\/5986"}],"wp:attachment":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5985"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5985"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5985"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}