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Questions tagged [memory]

Synonym for: RAM - Acronym for: Random Access Memory, a type of computer data storage.

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222 votes
13 answers
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Any benefit or detriment from removing a pagefile on an 8 GB RAM machine?

I'm running Windows 7 on a dual core, x64 AMD with 8 GB RAM. Do I even need a page file? Will removing it help or hurt performance? Would it make a difference if this is a server or a desktop? ...
Jason's user avatar
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207 votes
4 answers
285k views

Meaning of the buffers/cache line in the output of free

Why does my server show total used free shared buffers cached Mem: 12286456 11715372 571084 0 81912 6545228 -/+ buffers/cache: 5088232 7198224 Swap:...
Muahmmad Zeeshan's user avatar
178 votes
7 answers
362k views

What does Virtual memory size in top mean?

I am running top to monitor my server performance and 2 of my java processes show virtual memory of up to 800MB-1GB. Is that a bad thing? What does virtual memory mean? And oh btw, I have swap of ...
kapso's user avatar
  • 2,123
100 votes
18 answers
93k views

Caching/preloading files on Linux into RAM

I have a rather old server that has 4GB of RAM and it is pretty much serving the same files all day, but it is doing so from the hard drive while 3GBs of RAM are "free". Anyone who has ever tried ...
Andrioid's user avatar
  • 2,730
93 votes
16 answers
73k views

Why drop caches in Linux?

In our servers we have a habit of dropping caches at midnight. sync; echo 3 > /proc/sys/vm/drop_caches When I run the code it seems to free up lots of RAM, but do I really need to do that. Isn't ...
ivcode's user avatar
  • 1,072
84 votes
3 answers
169k views

How does vm.overcommit_memory work?

When I use the default settings: vm.overcommit_memory = 0 vm.overcommit_ratio = 50 I can read these values from /proc/meminfo file: CommitLimit: 2609604 kB Committed_AS: 1579976 kB But when ...
Mikhail Morfikov's user avatar
83 votes
9 answers
233k views

Dump a linux process's memory to file

Is it possible to dump the current memory allocated for a process (by PID) to a file? Or read it somehow?
Fragsworth's user avatar
  • 1,201
79 votes
5 answers
78k views

In Linux, what is the difference between "buffers" and "cache" reported by the free command?

This is an old question that I've seen from time to time. My understanding of it is rather limited (having read about the differences a long time ago, but the factoid(s) involved never really stuck). ...
Avery Payne's user avatar
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72 votes
10 answers
33k views

Linux: how to explicitly unswap everything possible?

I've launched something that took lots of memory and now everything lags a lot. I guess all applications' memory has gone to swap in order to free some space for the memory-intensive process, and now ...
kolypto's user avatar
  • 11.3k
69 votes
3 answers
126k views

How to read memory usage in htop?

Here is my htop output: For example, I'm confused by this ruby script: How much physical memory is it using? 3+1+8+51+51? 51? 51+51?
Lai Yu-Hsuan's user avatar
65 votes
2 answers
6k views

Does memtest86+ test memory which is used to run itself?

One of the common server failure scenarios is bad DRAM, sometimes even when ECC memory is used. memtest86+ is one of the most useful tools to diagnose DRAM problems. As it loads itself at the start ...
Robin's user avatar
  • 778
60 votes
5 answers
44k views

How to understand the memory usage and load average in linux server

I am using a linux server which has 128GB of memory and 24 cores. I use top to see how much it is used. Its output is pasted at the end of the post. Here are two questions: (1) I see that each of the ...
Tim's user avatar
  • 1,527
57 votes
4 answers
225k views

DIMMs: Single vs. Double vs. Quad Rank

What difference does the 'Rank' of DIMMs make to server memory? For example, when looking at server configurations I see the following being offered for the same server: 2GB (1x2GB) Single Rank PC3-...
MikeyB's user avatar
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57 votes
2 answers
10k views

vSphere education - What are the downsides of configuring VMs with *too* much RAM?

VMware memory management seems to be a tricky balancing act. With cluster RAM, Resource Pools, VMware's management techniques (TPS, ballooning, host swapping), in-guest RAM utilization, swapping, ...
45 votes
7 answers
114k views

How to find memory usage of individual Windows services?

Task Manager shows the overall memory usage of svchost.exe. Is there a way to view the memory usage of individual services? Note this is similar to Finegrained performance reporting on svchost.exe
Aidan Ryan's user avatar
  • 1,283
45 votes
8 answers
277k views

Get a history of CPU/memory usage

Is there someway to record Task Managers info about CPU and memory usage to examine later? Or an equivalent tool?
foobarfuzzbizz's user avatar
40 votes
5 answers
11k views

Should I be concerned that swap is being used on a host with nearly 40GB of free memory?

I have a production host, below: The system is using 1GB of swap, while maintaining nearly 40GB of free, unused memory space. Should I be concerned about this, or is it mostly normal?
MrDuk's user avatar
  • 895
40 votes
3 answers
32k views

Virtual Machine memory usage not appearing in TaskManager

There's something about Windows memory management and it's relationship to TaskManager that I don't understand and I'm hoping someone can enlighten me. If I'm running a virtual machine (doesn't ...
Scott Bussinger's user avatar
40 votes
5 answers
50k views

How do I get notified of ECC errors in Linux?

How do I get notified, when a Linux machine equipped with ECC memory recognizes a memory failure? I'm interested in both correctable and uncorrectable errors. if a message is written to dmesg/the ...
Jens Erat's user avatar
  • 1,613
39 votes
4 answers
166k views

Difference between 2Rx4 vs 2Rx8 RAM

My IT provider is convincing me there is no difference between a 2Rx4 and a 2Rx8 RAM. A little digging around informed me that x4 means 4 bits on a chip vs x8 means 8 bits. Which is good, but what ...
Shivku's user avatar
  • 391
38 votes
4 answers
32k views

Turn off the Linux OOM killer by default?

The OOM killer on Linux wreaks havoc with various applications every so often, and it appears that not much is really done on the kernel development side to improve this. Would it not be better, as a ...
Peter Eisentraut's user avatar
36 votes
5 answers
34k views

Unusually high dentry cache usage

Problem A CentOS machine with kernel 2.6.32 and 128 GB physical RAM ran into trouble a few days ago. The responsible system administrator tells me that the PHP-FPM application was not responding to ...
Wolfgang Stengel's user avatar
36 votes
8 answers
46k views

How to reduce memory usage on a Unix webserver

I'm currently using a Joyent Accelerator to host my webapps, and it's working fine, however I need to reduce costs so I'm downgrading my current plan and that imposes some new memory limits (256M rss, ...
User920951's user avatar
34 votes
8 answers
7k views

Is it necessary to burn-in RAM for server-class hardware?

Considering the fact that many server-class systems are equipped with ECC RAM, is it necessary or useful to burn-in the memory DIMMs prior to their deployment? I've encountered an environment where ...
ewwhite's user avatar
  • 199k
33 votes
7 answers
4k views

Database server: Small quick RAM or large slow RAM?

We are currently designing our new database servers, and have come up with a trade off I'm not entirely sure of how to answer. These are our options: 48GB 1333MHz, or 96GB 1066MHz. My thinking is ...
Josh Smeaton's user avatar
  • 1,360
33 votes
7 answers
54k views

Windows Server 2008 R2 Metafile RAM Usage

I have a server which runs Windows Server 2008 R2 x64 with 4GB of RAM which hosts around 2-3 million files, the majority of which are image files. Over a course of a week, I have noticed that ...
al2k4's user avatar
  • 433
32 votes
11 answers
21k views

To improve SQL performance, why not just put lots of RAM rather than having faster hard disks?

People keep telling me that in order to improve an SQL server's performance, buy the fastest hard disks possible with RAID 5, etc. So I was thinking, instead of spending all the money for RAID&...
user1034912's user avatar
  • 1,374
32 votes
3 answers
76k views

How to increase the amount of memory memcache uses?

I am currently on a Xeon 7550 server running Redhat x86_64 es5 with 32gb RAM. I have memcache installed and the only step remaining in the configuration is to set how much memory it uses. I had done ...
Peter Johansson's user avatar
31 votes
4 answers
29k views

What is ECC ram and why is it better?

I've seen a dicussion about ECC ram use on servers. Why is it better?
Toby Allen's user avatar
31 votes
2 answers
77k views

How to interpret output from Linux 'top' command?

Following a discussion made HERE about how PHP-FPM consuming memory, I just found a problem in reading the memory in top command. Here is a screenshot of my top just after restarting PHP-FPM. ...
Googlebot's user avatar
  • 1,077
29 votes
13 answers
61k views

Memory usage per user in Linux?

Let's say i have 20 users logged on my linux box. How can I know how much memory each of them is using?
Jakub Troszok's user avatar
29 votes
4 answers
60k views

What are the best possible ways to benchmark RAM (no-ECC) under linux / arm?

I want to test integrity and global performances of no-ECC memory chips on a custom board Are there some tools that run under linux so I can monitor system and global temperature in the same time ? ...
moul's user avatar
  • 565
28 votes
1 answer
48k views

Memory Usage Numbers In top/htop

Can someone please explain this top output. Each PHP process is using 30% of the total memory or of the used memory? Furthermore how can it be that the combined used memory across all the PHP ...
Mem's user avatar
  • 301
28 votes
3 answers
79k views

Page allocation failure - Am I running out of memory?

Lately, I've noticed entries like this one in the kern.log of one of my servers: Feb 16 00:24:05 aramis kernel: swapper: page allocation failure. order:0, mode:0x20 I'd like to know: What exactly ...
mfriedman's user avatar
  • 2,009
27 votes
10 answers
42k views

Would you use ECC RAM in a workstation?

Is ECC RAM recommended for use in workstations, or is it something that only gets used in servers? If non-ECC RAM works in PCs, why would we need ECC RAM at all?
Jon Tackabury's user avatar
26 votes
11 answers
64k views

Should you disable the page file with SSD?

I've been reading this question, and it has a lot of great information. But assuming you have more than enough RAM, I think the page file should be disabled on SSD to extend the life time. I know you ...
Pyrolistical's user avatar
26 votes
3 answers
41k views

Linux not freeing large disk cache when memory demand goes up

Running Ubuntu on a 2.6.31-302 x86-64 kernel. The overall problem is that I have memory in the 'cached' category that keeps on going up and will not be freed or used even when our application needs it....
xxx's user avatar
  • 501
25 votes
6 answers
63k views

How can I tell how much RAM is installed on a FreeBSD server?

As per the title: How can I tell how much RAM is installed on a FreeBSD server? Thanks!
Ben's user avatar
  • 405
24 votes
3 answers
30k views

Cent OS: How do I turn off or reduce memory overcommitment, and is it safe to do it?

From time to time "my" server stalls because it runs out of both memory and swap space. (it keeps responding to ping but nothing more than that, not even ssh). I'm told linux does memory ...
matteo's user avatar
  • 727
24 votes
6 answers
14k views

Would upgrading RAM in a HP LaserJet printer improve its performance?

Would RAM upgrade for an HP 4050N LaserJet printer matter? We have this real workhorse of a Laser Printer. It's an HP 4050N and it's been in use for many years. In the past few years, I've noticed ...
Edward_178118's user avatar
23 votes
3 answers
185k views

What is the difference between RDIMM vs UDIMM

I don't quite understand the differences between the two besides the obvious price differences. What does each offer over the other?
Tablemaker's user avatar
  • 1,159
22 votes
4 answers
25k views

How much contention is too much in VMware?

For a while now I've been trying to figure out why quite a few of our business-critical systems are getting reports of "slowness" ranging from mild to extreme. I've recently turned my eye to the ...
Chuck Herrington's user avatar
22 votes
2 answers
69k views

Best MySQL cache settings for 8gb RAM dedicated MySQL server using only InnoDB (5gb database)

I'm a pretty big noob when it comes to setting up MySQL for performance. And honestly I'm not worried about the fine tuning to squeeze every last bit of performance out of MySQL, but I do know that ...
billmalarky's user avatar
22 votes
6 answers
34k views

What consumes memory in java process?

we are trying to investigate memory usage of java process under moderate load. PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 12663 test 20 0 8378m 6.0g 4492 S 43 8.4 ...
Konstantin S.'s user avatar
22 votes
4 answers
6k views

Can MySQL effectively take advantage of 64 GB RAM?

We have been running into a problem where querying a table that has approximately 50 million rows, and has an index size of 4 GB (table size of about 6 GB) results in the database server swapping ...
Galen's user avatar
  • 323
21 votes
6 answers
64k views

How to have linux top command show memory summary in megabytes not kilobytes

Redhat EL5 I had my top configured the just the way I like showing the memory summary and swap summary in MB. I had to close my shell and then when I re-opened it, it is back showing in (default ?) ...
Michael Irey's user avatar
21 votes
2 answers
23k views

How is memory usage reported in Linux?

Using ps, I can see the size, the vsize (same as top's VIRT?), and the rss (same as top's RES?). (One more I see in top is SHR.) Could someone summarize for me what these different fields mean?
Jim Hunziker's user avatar
  • 1,862
21 votes
3 answers
15k views

Non-ECC memory with ZFS: a stupid idea?

I have a new server and am planning to upgrade the paltry 2 GB of memory to the maximum of 16 GB. (Theoretically 8 GB is the limit, but empirically 16 GB has been shown to work.) Some guides advise ...
iconoclast's user avatar
  • 1,850
21 votes
5 answers
46k views

How to check if RAM is running in ECC mode?

I updated this post since I replaced the processor, but the core of my question (and unfortunately the results as well) are the same. I built my first FreeNAS box and wanted to use ECC RAM since I ...
comfreak's user avatar
  • 1,541
21 votes
3 answers
2k views

What is the Rowhammer DRAM bug and how should I treat it?

DRAM chips are very tightly packed. Research has shown that neighboring bits can be flipped at random. What is the probability of the bug triggering at random in a server-grade DRAM chip with ECC (...
Deer Hunter's user avatar
  • 1,090

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