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Showing entries 1 to 11

Displaying posts with tag: Kernel (reset)

OOM relation to vm.swappiness=0 in new kernel
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I have recently been involved in diagnosing the reasons behind OOM invocation that would kill the MySQL server process. Of course these servers were primarily running MySQL. As such the MySQL server process was the one with the largest amount of memory allocated.

But the strange thing was that in all the cases, there was no swapping activity seen and there were enough pages in the page cache. Ironically all of these servers were CentOS 6.4 running kernel version 2.6.32-358. Another commonality was the fact that vm.swappiness was set to 0. This is a pretty much standard practice and one that is applied on nearly every server that runs MySQL.

Looking into this further I realized that there was a change introduced in kernel 3.5-rc1 that altered the swapping behavior when “vm.swappiness=0″.

Below is the description of the commit that

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on swapping and kernels
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There is much more to write about all the work we do at Facebook with memory management efficiency on our systems, but there was this one detour investigation in the middle of 2012 that I had to revisit recently courtesy of Wikipedia.

There are lots of factors that make machines page out memory segments into disk, thus slowing everything down and locking software up – from file system cache pressure to runaway memory leaks to kernel drivers being greedy. But certain swap-out scenarios are confusing – systems seem to have lots of memory available, with proper settings file system cache should not cause swapping, and obviously in production environment all the memory leaks are ironed out.

And yet in mid-2012 we noticed that our new kernel machines were swapping out for no obvious reason. When it comes to swapping, MySQL community will always point to Jeremy’s post on

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Storage caching options in Linux 3.9 kernel
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dm-cache is (albeit still classified “experimental”) is in the just released Linux 3.9 kernel. It deals with generic block devices and uses the device mapper framework. While there have been a few other similar tools flying around, since this one has been adopted into the kernel it looks like this will be the one that you’ll be seeing the most in to the future. It saves sysadmins the hassle of compiling extra stuff for a system.

A typical use is for an SSD to cache a HDD. Similar to a battery backed RAID controller, the objective is to insulate the application from latency caused by the mechanical device, the most laggy part of which is seek time (measured in milliseconds). Giventhe  relatively high storage capacity of an SSD (in the hundreds of GBs), this allows you to mostly disregard the mechanical latency for writes and that’s very useful for

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Activity of the ZFS ARC
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Disk I/O is still a common source of performance issues, despite modern cloud environments, modern file systems and huge amounts of main memory serving as file system cache. Understanding how well that cache is working is a key task while investigating disk I/O issues. In this post, I’ll show the activity of the ZFS file system Adaptive Replacement Cache (ARC).

There are often more statistics available than you realize (or have been documented), which may certainly be true with the ARC. Apart from showing these statistics, I’ll also show how to extend observability using dynamic tracing (DTrace). These tracing techniques are also applicable to any kernel subsystem. This is an advanced topic, where I’ll sometimes dip into kernel code.

Architecture

For background on the ZFS ARC, see the paper

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SAP Netweaver 7.0, ERP 6.0, CRM 5.0, CRM 2007, SCM 5.0, SCM 5.1, SRM 5.0 are support for ABAP stack on Solaris 11
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using one of the two databases

  • Oracle 11.2.0.3
  • MaxDB 7.8.2.26 

with SAP Kernel 7.20_ext are supported on Solaris 11. The details are documented in the SAP note 1643799 (access for SAP customers only).

We’re in!
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DRBD has entered a new phase. After being developed out of tree for 9 years, and after an extended review and streamlining phase since March, Phil submitted DRBD to be merged into 2.6.32 release of the Linux mainline kernel. The submission was accepted by block layer maintainer Jens Axboe, who merged DRBD in September, then deferred to the 2.6.33 merge window, and this morning Linus

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Microsoft contributes to Linux kernel: a CAOS Theory Q&A
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Microsoft has announced that it is to contribute code to the Linux kernel development effort under the GNU General Public License (GPL) v2. What on earth does it all mean? Here’s our take on the situation. With thanks to Jay Lyman for his contribution to the following:

Q. This is a joke, right?

A. Not at all, although if any announcement is better suited to the image above, we can’t think of one. Microsoft has announced that it is going to contribute code to Linux under the GPLv2.

Q. What code is Microsoft

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Linux 2.6.29
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2.6.29 was released. I don’t usually write about linux kernel releases, thats what Slashdot is for :), but this one introduces write barriers in LVM, as well as ext4 with write barriers enabled by default. If you run this kernel and forget to turn off barrier support at filesystems (like XFS, nobarrier), you will see nasty performance slowdowns (recent post about it). Beware.

XenServer 5 with OpenBSD
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Here is my experience trying to run OpenBSD with XenServer 5 Enterprise.

  • XenServer console doesn’t function properly as it keeps overlaying text displayed previously or anything you have typed into the console. Makes it very difficult to read and see what you are doing. As well it appears numerpad with numlock on does not work either. The best work around is to SSH into OpenBSD.
  • Receiving the following error messages at boot up, “clock: unknown CMOS layout” and “rl0: watchdog timeout”. Yes the NIC is being detected as a Realteak 8139. If I check /var/run/dmesg.boot out of the two error messages I only see the “clock: unknown CMOS layout”. So I would assume the watchdog timeout
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What does an opensource project need ?
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besides a community ?

Some people think that apart from a community and users you also need an infrastructure to support these users.

Murray ignited the discussion by pointing us to the fact that PostgreSQL doesn't have a bugzilla to report an track issues.

Different projects have different approaches. Both the kernel, Drupal and MySQL have build their own infrastructure. Others choose Sourceforge for their projects.

What's your approach ?

DRBD 8.2.3 released; boasts online device verification, CPU affinity optimization
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DRBD 8.2.3 was released today. Even though just a micro release in terms of version numbering, it comes with a couple of very handy brand new features: on-line device verification, and tunable processor affinity.
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Showing entries 1 to 11

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