cache is a component that stores data so future requests for that data can be served faster; the data stored in a cache might be the results of an earlier computation, or the duplicates of data stored elsewhere.

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How to enable a non-root user to empty the linux buffer cache

I'm required to empty the linux buffer cache in a python script, that runs on a Debian wheezy VM. As root I run sync; echo 3 | sudo tee /proc/sys/vm/drop_caches, but the script is run by a user, ...
7
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1answer
1k views

List all files that are present in the cache

This question answers to the question on how to find the what is part of cache. However, in the fincore executable you have to pass the filename to check if it is part of cache. Is there a tools or a ...
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3answers
194 views

Buffering (named) pipe in GNU OS

In the GNU OS a process can only write data to a pipe if another process reads the same data (from the same pipe) at the same time. Is there something like a pipe which lets the 1st process write and ...
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0answers
53 views

How shareable is /var/cache?

I know that some subdirectories of /var/cache are pretty much shareable, for example /var/cache/pacman (in case of ArchLinux), and possibly others (/var/cache/man?), but at least /var/cache/ldconfig ...
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2answers
68 views

Increasing performance of clear text file reads

In our bioinformatics application we have large files (up to 900MB, typically 100MB). These files contain a clear text representation of a genome, and are essentially a 1 line file with a sequence of ...
1
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1answer
342 views

Request header for Cache-Control not working

I have set Cache-Control in apache for 1 week for my JS Files but when i check in the browser Cache-Control shows no-cache. Where i am missing the configuration ? Below is my configuration in apache ...
4
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1answer
101 views

Avoid -dbg_version packages on apt-cacher-ng server

Intro: We have created a apt-cacher-ng server to provide cached packages to our users that have Ubuntu 14.04 installed. Combined with the cached packages, we are doing a weekly "mirror" of some Ubuntu ...
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2answers
145 views

Memcached on a webserver

We host a Magento webshop hosted by Amazon EC2, and we have speed issues. We're currently looking at moving to another provider. We found one hosting provider where we have a test account now. Speed ...
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0answers
38 views

Very strange issue, something is blocking specific links on local domain

I have a very strange issue and I ran out of ideas. The major problem is that the symptoms are not consistent. I have a short link website hosted on 2 virtual machines, one with nginx+php-fpm and one ...
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1answer
352 views

file access time after loading file into the cache

I read from here that I could load file into RAM for faster accessing using the below command. cat filename > /dev/null However, I wanted to test if the above statement is really true. So, I ...
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1answer
346 views

Difference between route cache and neighbor table

Our Ubuntu server runs as a router for thousands of devices. With the growing number of connecting clients we have noticed 3 overflow problems in the kernel log: 1. Route cache chain too long 2. ...
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0answers
434 views

Ubuntu: Restore not printed document from browser cache

I was at work today faced with a situation where I have to prove that I did not make a mistake. Without going into detail, yesterday I generated an important document which was to be printed. For ...
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1answer
152 views

What is being cached?

I have an embedded system with a low amount of memory. The system has allocation issues. Maybe due to fragmentation: Memory allocation issue on NOMMU? The platform is a NOMMU platform and so I suspect ...
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1answer
64 views

What dev folder allows you tell the OS to cache something?

Someone told me that there is a sub folder off of dev that basically allows you to tell the OS to keep the contents of that folder cached in RAM. So if I put some files & directories in ...
4
votes
1answer
577 views

Fix “Route hash chain too long” without restart

On our production server (ubuntu 12.04, 3.2.0-63 kernel) routing cache reached its capacity. Modifying rhash_entries is out of the question, since it is a kernel boot param, and we can not restart the ...
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2answers
456 views

How should I restore /var/cache?

I just restored my Raspberry Pi server from an rsync image. During the backup, I had excluded /var/cache/*, thinking that this would restore an empty directory. This worked, but when I rebooted, a ...
3
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1answer
453 views

Spawn multiple dirty page flusher threads per device

In earlier 2.6.X kernels, pdflush was used and it would spawn more pdflush threads if all current pdflush threads were busy for a second (read from The Linux Page Cache and pdflush). Since the ...
3
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1answer
132 views

Artificially prime buffer cache?

Is it beneficial to artificially prime the buffer cache when dealing with larger files? Here's a scenario: A large file needs to be processed, line by line. Conceptually, it is easy to parallelize ...
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0answers
18 views

how to find where buffers/cache are and how to clean them up? [duplicate]

I want to create 20gb ram disk for ANSYS to work in yet on free -g I see: And personally I have not created any ram drives yet. So I wonder how to maximize avaliable ram: how to locate what is using ...
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0answers
193 views

Reduce cache size of flash storage devices

For various benefits Linux uses a memory cache for writes to removable stogare devices like memory sticks. This cache seems to be quite large on my system, which leads to some annoying behavior. For ...
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0answers
74 views

In meminfo, sometimes Mapped more than Cached

In /proc/meminfo, AFAIK Cached >= Mapped But after /proc/sys/vm/drop_caches, it goes to Cached < Mapped Cached: 66132 kB Mapped: 67792 kB /proc/meminfo contents ...
4
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1answer
14k views

Is no caching mode page a serious error?

My server log displays the following error messages in RED: kernel: sda: sda1 sda2 kernel: sd 0:1:0:0: [sda] No Caching mode page found kernel: sd 0:1:0:0: [sda] Assuming drive cache: write through ...
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0answers
123 views

Figuring out physical cache layout in FreeBSD

I'm trying to figure out they physical cache layout of my CPU in FreeBSD 10. I see the following from sysctl kern.sched.topology_spec kern.sched.topology_spec: <groups> <group level="1" ...
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2answers
209 views

Random application crashes in Linux

Sometimes after booting my computer, some applications fail to start: they crash. They're usually the largest ones, such as firefox, thunderbird or virtualbox. Rebooting or cleaning the cache usually ...
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1answer
319 views

should I reduce /dev/shm size?

I have a server wity 8 GB RAM Mem: Total 8031464 Used 5146344 Free 2885120 If I execute # df it always returns this tmpfs 4015732 0 4015732 0% /dev/shm What does it ...
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1answer
1k views

Clear Memory Cache on Amazon EC2

In our project we have a few tests which run for about 3-4 hours continuously. In due course, the tests fail as they couldn't find enough memory. On googling, I found that running the following ...
7
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1answer
878 views

How to use an SSD for caching, so my hard disks can spin down?

I've got a file server with a bunch of disks running together in a BTRFS pool and want to add an SSD for caching. I'm not mainly after speeding up things, but want to catch the regular small accesses ...
3
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3answers
883 views

Speed up copying 1000000 small files

I have 1000000 4-20 kb files in a dir. I need to copy that dir. But it seems I have to do a seek for each files so this takes quite a while. Is there a way in which I can speed this up? I am ...
9
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2answers
4k views

what does it mean by cold cache and warm cache concept?

I read a paper and it used terms “cold cache” and “warm cache”. What does it mean by cold cache and warm cache concept? I visit this but I need something more.
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1answer
524 views

flashcache tuning

I installed flashcache version 3.1.1 and created a write-back cache. The performance is good as long as the percentage of dirty blocks is not too high. My application does heavy I/O at the ...
0
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1answer
74 views

Is there a way to prevent SWAP from collecting cached data?

Here is the following info: Do I need more swap? No, disk caching only borrows the ram that applications don't currently want. It will not use swap. If applications want more memory, they ...
1
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1answer
2k views

How to find the page size, associativity, and TLB size and number of entries?

Under an Ubuntu system, are there commands for looking up: the page size, n in n-way cache associativity, TLB cache's size and number of entries?
1
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1answer
360 views

When speaking about cache size of a CPU, we only need the size of the cache at the furthest level [closed]

When speaking about cache size of a CPU, do we only need to know the size of the cache at the furthest level (such as at level 3, when the cache hierachy is 3-level)? Instead of the sum of all the ...
2
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1answer
537 views

Web server seems to keep serving old images, issue with Apache & VirtualBox?

I'm asking this here because I'm pretty sure it's a Linux issue. I'm running Apache server locally on Ubuntu Server 12.10, which runs inside a virtual machine (VirtualBox) on Windows 7. The "www" ...
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1answer
69 views

How to print a Bind10 cache dump?

How can you print the current state of the bind10 cache? I searched the bind10 manual and tried to figure it out using bindctl.
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2answers
4k views

Clear file system cache on AIX

I'm using AIX 6.1 and for testing. I want to clear the file system cache. Something similar a this on linux : echo 2 > /proc/sys/vm/drop_caches Is this possible?
4
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2answers
1k views

SSD as a read cache for FREQUENTLY read data

I'm looking for ways to make use of an SSD to speed up my system. In “Linux equivalent to ReadyBoost?” (and the research that triggered for me) I've learned about bcache, dm-cache and EnhanceIO. All ...
2
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0answers
786 views

Route all HTTP traffic through polipo

I've set up polipo on my machine to listen to the default port 8123. To test it, I set the in-memory cache to a ridiculously high 2 GB and downloaded a 50 MB file using wget utilizing the proxy. ...
2
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0answers
73 views

Too large cache causes disks to grind, I/O to drop

This is a followup question to my earlier problem. In short I was experiencing massive I/O drops together with not-so-violent disk grinding, and with help I found out that the big caches were the ...
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2answers
2k views

DNSCrypt, Unbound and DNSSEC

I would like to have an encrypted DNS queries + a DNS Cache + Domain Name System Security Extensions (DNSSEC) . I used this bash script to install DNSCrypt and I choosed to use dnscrypt.eu servers : ...
3
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0answers
1k views

Tune write disk cache flushing algorithm

I would like to use the free memory for write cache. Linux does that automatically, but it has some weird flushing algorithm that I would like tuned for my use. I have recently used ddrescue to copy ...
1
vote
1answer
129 views

External Cache not socketed

When I check my CPU Cache with command dmidecode, I get Cache configuration to be Not Socketed. What does that mean? prayag@prayag:~/hacker_/draobkcalb$ sudo dmidecode -t cache # dmidecode 2.11 ...
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2answers
5k views

How to reduce buffers\cache

A monitoring system keeps alerting that my machine is reaching\breaking through it's RAM utilization threshold which is 15 GBs. I've done some reading and understood that the apparent RAM utilization ...
8
votes
1answer
776 views

Cleanup of temporary file ~/.cache/duplicity/temp failed

Often when I run Duplicity I see an error message like this at the end of the run: Cleanup of temporary file ...
1
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2answers
116 views

Configurable DNS cache for Linux

What I need is to configure a Linux machine, so that when user of that machine goes to www.somesite.com he/she is redirected to, say, 127.0.0.1. What is the best way to achieve it?
2
votes
1answer
95 views

Monitoring file reads for cache warming

After adding more memory to my Linux machine I was tempted to use the cache more agressively. The thing is: I boot up my machine, go to bathroom, come back and log in. It takes like half a minute to ...
115
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1answer
237k views

How do you empty the buffers and cache on a Linux system?

Prior to doing some benchmarking work how would one free up the memory (RAM) that the Linux Kernel is consuming for its buffers and cache?
4
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3answers
1k views

Are there any ways or tools to dump the memory cache and buffer?

As the title, I want to check out what files are loaded in buffer. Just so it's clear, the buffers & cache I'm referring to are what show up when you run the free -m command: $ free -m ...
3
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1answer
5k views

Is “sync” before drop_caches necessary?

I have read a lot of docs saying, it is good idea to do a sync before doing echo [1,2,3] > /proc/sys/vm/drop_caches. I am not able to understand why it is needed, since drop_cache is a ...
5
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2answers
1k views

Find/ls caching

It seems as though the first time I run find or ls on a directory, it takes a while to work. But, each time thereafter, it is fast, as though a list of the directory's contents has been cached or ...