Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [performance]

Questions about server hardware and software performance, or network performance.

127
votes
4answers
171k views

FreeBSD performance tuning: Sysctl parameter, loader.conf, kernel

I wanted to share knowledge of tuning FreeBSD via sysctl.conf / loader.conf / KENCONF / etc. It was initially based on Igor Sysoev's (author of nginx) presentation about FreeBSD tuning up to 100,000-...
123
votes
13answers
49k views

Are networks now faster than disks?

This is a software design question I used to work on the following rule for speed cache memory > memory > disk > network With each step being 5-10 times the previous step (e.g. cache ...
101
votes
8answers
19k views

How can a single disk in a hardware SATA RAID-10 array bring the entire array to a screeching halt?

Prelude: I'm a code-monkey that's increasingly taken on SysAdmin duties for my small company. My code is our product, and increasingly we provide the same app as SaaS. About 18 months ago I moved ...
89
votes
8answers
181k views

What limits the maximum number of connections on a Linux server?

What kernel parameter or other settings control the maximum number of TCP sockets that can be open on a Linux server? What are the tradeoffs of allowing more connections? I noticed while load testing ...
88
votes
4answers
16k views

Why is TCP accept() performance so bad under Xen?

The rate at which my server can accept() new incoming TCP connections is really bad under Xen. The same test on bare metal hardware shows 3-5x speed ups. How come this is so bad under Xen? Can you ...
86
votes
25answers
145k views

How to copy a large number of files quickly between two servers

I need to transfer a huge amount of mp3s between two serves (Ubuntu). By huge I mean about a million files which are on average 300K. I tried with scp but it would have taken about a week. (about 500 ...
77
votes
6answers
175k views

High load average, low CPU usage - why?

We're seeing huge performance problems on a web application and we're trying to find the bottleneck. I am not a sysadmin so there is some stuff I don't quite get. Some basic investigation shows the ...
71
votes
6answers
92k views

Software vs hardware RAID performance and cache usage

I've been reading a lot on RAID controllers/setups and one thing that comes up a lot is how hardware controllers without cache offer the same performance as software RAID. Is this really the case? I ...
61
votes
10answers
15k views

How to [politely?] tell software vendor they don't know what they're talking about

Not a technical question, but a valid one nonetheless. Scenario: HP ProLiant DL380 Gen 8 with 2 x 8-core Xeon E5-2667 CPUs and 256GB RAM running ESXi 5.5. Eight VMs for a given vendor's system. ...
50
votes
8answers
25k views

How much of a performance hit for https vs http for apache?

Roughly how much of a performance hit will https take compared to http for the same page? Suppose I can handle 1000 requests/s for abc.php, how much will it decrease by when accessed through https? I ...
49
votes
12answers
63k views

Is virtual machine slower than the underlying physical machine?

This question is quite general, but most specifically I'm interested in knowing if virtual machine running Ubuntu Enterprise Cloud will be any slower than the same physical machine without any ...
44
votes
5answers
114k views

Howto check disk I/O utilisation per process

Im having a problem with a stalling Linux system and I have found sysstat/sar to report huge peaks in disk I/O utilization, average service time as well as average wait time at the time of the system ...
44
votes
6answers
37k views

Which PHP (opcode) cache one should use and why?

I keep hearing about some PHP (opcode) caches like - APC, XCache, Memcache, eAccelerator, etc. But I couldn't ever figure out how to go about choosing one. Apart from performance benefit, which a ...
43
votes
11answers
76k views

What can cause slow ssh session? [closed]

I ssh on remote host but terminal performance is poor. Symbols I am typing are not shown immediately, but with some delay. Sometimes two symbols are shown at one time after delay.
41
votes
7answers
68k views

How can you know what is w3wp.exe doing? (or how to diagnose a performance problem)

I'm having a performance problem in a site we've made, and I'm not exactly sure how to start diagnosing it. The short description is: We have a very small site (http://hearablog.com) with very little ...
40
votes
4answers
87k views

Why is my rsync so slow?

My Laptop and my workstation are both connected to a Gigabit Switch. Both are running Linux. But when I copy files with rsync, it performs badly. I get about 22 MB/s. Shouldn't I theoretically get ...
39
votes
5answers
8k 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?
38
votes
6answers
40k views

Process runs slower as a scheduled task than it does interactively

I have a scheduled task which is very CPU- and IO-intensive, and takes about four hours to run (building source code, if you're curious). The task is a Powershell script which spawns various sub-...
37
votes
1answer
47k views

Is there still a use for irqbalance on modern hardware?

This question has been asked before, but I believe that the world has changed enough for it to be asked again. Does irqbalance have any use on today’s systems where we have NUMA-capable CPUs with ...
35
votes
17answers
66k views

What network file sharing protocol has the best performance and reliability? [closed]

We have a setup with a few web servers being load-balanced. We want to have some sort of network shared storage that all of the web servers can access. It will be used as a place to store files ...
35
votes
7answers
62k views

Xen vs. KVM in performance

What is faster on the same hardware, Xen or KVM? I'm trying to pick-up a virtualization technology to work, which gives the best performance. There are some benchmarks here that I found on the ...
35
votes
5answers
2k views

Pay no attention to that SAN behind the curtain

Once upon a time, I built my own SQL servers, and had control over drive configuration, RAID levels, etc. The traditional advice of separation of data, logs, tempdb, backups, (depending on budget!) ...
34
votes
5answers
42k views

How can I find out what is causing interrupts on Windows?

Occasionally I come across servers (Windows 2003 and 2008) with high processor % interrupt time. Is there a way to see what program or device is causing the interrupts?
34
votes
5answers
75k views

How many Context Switches is “normal” (as a function of CPU cores (or other))?

Hi Linux/UNIX Overlords, Do any of you have a rule of thumb as to how many context switches (per processor core) is Normal on a Linux server? My college here brought it up, and he's seeing 16K on a ...
33
votes
2answers
4k views

Why is my bare-metal 16x 2.93GHz cores computer performing poorer than a VPS with 4x 2.5GHz cores?

I have a written a piece of multi-threaded software that does a bunch of simulations a day. This is a very CPU-intensive task, and I have been running this program on cloud services, usually on ...
33
votes
2answers
30k views

Can rsync display current average speed?

When I'm transferring large quantities of data using rsync, it would be helpful if I could have the average speed up until now at a glance, rather than a bunch of different speeds for each file.
32
votes
11answers
27k views

How to make `rm` faster on ext3/linux?

I have ext3 filesystem mounted with default options. On it I have some ~ 100GB files. Removal of any of such files takes long time (8 minutes) and causes a lot of io traffic, which increases load on ...
31
votes
8answers
9k views

Why do IOPS matter?

I understand what IOPS and throughput are. Throughput measures data flow as MB/s and IOPS says how many I/O operations are happening per second. What I don't understand is why many storage services ...
31
votes
9answers
14k 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&...
31
votes
4answers
38k views

OpenVPN performance: how many concurrent clients are possible?

I am evaluating a system for a client where many OpenVPN clients connect to a OpenVPN server. "Many" means 50000 - 1000000. Why do I do that? The clients are distributed embedded systems, each ...
30
votes
5answers
5k views

Why does it take tens of seconds to get a shell prompt?

It's a sort of regular occurrence that, after SSHing to a server (or even opening a terminal on my Mac), the login banner prints immediately but it takes ~10 seconds to a minute for the shell prompt ...
30
votes
11answers
50k views

How to monitor and log the memory/cpu usage of processes over time? [closed]

I am looking for a way to diagnose issues, such as swap death, where a balooning memory process fills up swap and kills the whole machine (such as apache). I'm already using cacti and I can set up ...
30
votes
3answers
12k views

PHP: What are the advantages of FastCGI over mod_php?

It was recently suggested to me that I use FastCGI with PHP. Now I went to the FastCGI page and read it but I don't really understand what the advantages are.
29
votes
5answers
7k views

bzip2 too slow. Multiple cores are avaible

I am running this command: pg_dumpall | bzip2 > cluster-$(date --iso).sql.bz2 It takes too long. I look at the processes with top. The bzip2 process takes about 95% and postgres 5% of one core. ...
29
votes
8answers
9k views

Delete 10M+ files from ZFS, effectively

I have written a buggy program that has accidentally created about 30M files under /tmp. (The bug was introduced some weeks ago, and it was creating a couple of subdirectories per second.) I could ...
29
votes
3answers
70k views

Optimal values for ServerLimit, MaxClients, MaxRequestsPerChild directives

I'm running a traffic intense site plenty of dynamic content, mostly user-generated. The server is a dedicated one and has a total of 4 Intel(R) Xeon(R) CPU X3210 @ 2.13GHz proccesors. I need to know ...
29
votes
7answers
20k views

What are the performance differences between Raid 0,1,5,6,10

I have heard/read different performance stories on the various raid flavors. I am curious what the agreed upon best answer is.
28
votes
4answers
45k views

How do I run my PowerShell scripts in parallel without using Jobs?

If I have a script that I need to run against multiple computers, or with multiple different arguments, how can I execute it in parallel, without having to incur the overhead of spawning a new PSJob ...
28
votes
7answers
16k views

Is it OK to run perfmon on production servers? And why?

Or should perfmon be limited to a Dev/QA server with load tests that simulate production activity? I'd like to run perfmon for two days (like Sql Server master Brent Ozar suggests) to get an overall ...
28
votes
8answers
8k views

Write speed requirement : 1.1GB/s possibilities?

We will have a machine at work, that on peak performance, should be able to push 50 ("write heads") x 75GB of data per hour. That's peak performance of ~1100MB/s write speed. To get that from the ...
28
votes
5answers
5k views

What are the performance implications for millions of files in a modern file system?

Let's say we're using ext4 (with dir_index enabled) to host around 3M files (with an average of 750KB size) and we need to decide what folder scheme we're going to use. In the first solution, we ...
27
votes
4answers
34k views

Why VM snapshots are affecting performance?

I read in one of the VMware KB articles that snapshots will directly affect VM performance. But my team keeps asking me how snapshots can affect performance. I would like to give them solid reason ...
26
votes
5answers
54k views

How to identify I/O bottlenecks on a Linux server?

How do you determine that the performance of your Linux server is I/O bound and, perhaps more importantly, what process or processes are casuing the problem?
26
votes
4answers
25k views

Limit Linux background flush (dirty pages)

Background flushing on Linux happens when either too much written data is pending (adjustable via /proc/sys/vm/dirty_background_ratio) or a timeout for pending writes is reached (/proc/sys/vm/...
26
votes
1answer
1k views

Unexpected and unexplained slow (and unusual) memory performance with Xeon Skylake SMP

We've been testing a server using 2x Xeon Gold 6154 CPUs with a Supermicro X11DPH-I motherboard, and 96GB RAM, and found some very strange performance issues surrounding memory when compared to ...
25
votes
5answers
30k views

Can a pool of memcache daemons be used to share sessions more efficiently?

We are moving from a 1 webserver setup to a two webserver setup and I need to start sharing PHP sessions between the two load balanced machines. We already have memcached installed (and started) and ...
25
votes
11answers
18k views

Are there any good reasons for disabling hardware-assisted virtualization?

We've had a number of servers from Dell recently, all of which have had hardware-assisted virtualization disabled in the BIOS. As far as I know hardware-assisted virtualization is a good thing - so ...
25
votes
6answers
54k views

Incredibly low KVM disk performance (qcow2 disk files + virtio)

I'm having some serious disk performance problems while setting up a KVM guest. Using a simple dd test, the partition on the host that the qcow2 images reside on (a mirrored RAID array) writes at ...
24
votes
4answers
31k views

How to pick between RabbitMQ and ZeroMQ or something else?

I'm looking for a queuing system which is fast and reliable and potentially can be spread across machines. Platform is Linux. Open source is preferable. Both RabbitMQ and ZeroMQ look good but I ...
24
votes
3answers
22k views

How much overhead does x86/x64 virtualization have?

How much overhead does x86/x64 virtualization (I'll probably be using VirtualBox, possbly VMWare, definitely not paravirtualization) have for each of the following operations a Win64 host and Linux64 ...