..
Copyright (c) 2012-2016 Varnish Software AS
SPDX-License-Identifier: BSD-2-Clause
See LICENSE file for full text of license
Platform specific notes
------------------------
On some platforms it is necessary to adjust the operating system before running
Varnish on it. The systems and steps known to us are described in this section.
On Linux, use tmpfs for the workdir
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Varnish uses mapped files for shared memory, for which performance depends on
writes not blocking. On Linux, however, write throttling implemented by some
file systems (which is generally useful in other scenarios) can interact badly
with the way Varnish works and cause lockups or performance impacts. To avoid
such problems, it is recommended to use a ``tmpfs`` "virtual memory file system"
as the *workdir*.
To ensure ``tmpfs`` is used, check the following:
Determine the *workdir*. If you use a specific ``-n`` option to ``varnishd`` or
set the ``VARNISH_DEFAULT_N`` variable, it is that value. Otherwise run
``varnishd -x options``, which outputs the *workdir* default.
Run ``df *workdir*``. If it reports ``tmpfs`` as the file system in the first
column, no additional action is necessary.
Otherwise, consider creating a ``tmpfs`` mountpoint at *workdir*, or configure
*workdir* on an existing ``tmpfs``.
The ``tmpfs`` for *workdir* should be mounted with Transparent Hugepage
disabled. Consider mounting the working directory with the ``huge=never`` mount
option if that is not the default.
Note: Very valid reasons exist for *not* following this recommendation, if you
know what you are doing.
workdir can not be mounted ``noexec``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Varnish compiles VCL to a shared object and needs to load it at runtime. So the
*workdir* can not reside on a file system mounted with ``noexec``.
Lift locked memory limits
~~~~~~~~~~~~~~~~~~~~~~~~~
For the same reason as explained above, varnish tries to lock shared memory in
RAM. Therefore, the locked memory limit should ideally be set to unlimited or
sufficiently high to accommodate all mapped files. The specific minimum required
value is dynamic, depending among other factors on the number of VCLs loaded and
backends configured. As a rule of thumb, it should be a generous multiple of the
size of *workdir* when varnish is running.
See :ref:`ref-vsm` for details.
.. _platform-thp:
Transparent Hugepage on Linux
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On certain Linux distributions Transparent Hugepage (THP) kernel support is
enabled by default. This is known to cause instabilities of Varnish.
By default, Varnish tries to disable the THP feature, but does not fail if it
can't. The ``linux`` :ref:`ref-varnishd-opt_j` offers to optionally enable,
disable or ignore THP.
Alternatively, THP can be disabled system-wide. If Varnish is the only
significant service running on this system, this can be done during runtime
with::
echo never > /sys/kernel/mm/transparent_hugepage/enabled
The setting can be also be persisted in the bootloader configuration by adding
``transparent_hugepage=never`` to the kernel command line.
OpenVZ
~~~~~~
It is possible, but not recommended for high performance, to run
Varnish on virtualised hardware. Reduced disk and network -performance
will reduce the performance a bit so make sure your system has good IO
performance.
If you are running on 64bit OpenVZ (or Parallels VPS), you must reduce
the maximum stack size before starting Varnish.
The default allocates too much memory per thread, which will make Varnish fail
as soon as the number of threads (traffic) increases.
Reduce the maximum stack size by adding ``ulimit -s 256`` before starting
Varnish in the init script.
TCP keep-alive configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On some Solaris, FreeBSD and OS X systems, Varnish is not able to set the TCP
keep-alive values per socket, and therefore the *tcp_keepalive_* Varnish runtime
parameters are not available. On these platforms it can be beneficial to tune
the system wide values for these in order to more reliably detect remote close
for sessions spending long time on waitinglists. This will help free up
resources faster.
Systems that does not support TCP keep-alive values per socket include:
- Solaris releases prior to version 11
- FreeBSD releases prior to version 9.1
- OS X releases prior to Mountain Lion
On platforms with the necessary socket options the defaults are set
to:
- `tcp_keepalive_time` = 600 seconds
- `tcp_keepalive_probes` = 5
- `tcp_keepalive_intvl` = 5 seconds
Note that Varnish will only apply these run-time parameters so long as
they are less than the system default value.
.. XXX:Maybe a sample-command of using/setting/changing these values? benc
Henceforth, whatever our philosopher says about Matter will apply to extension and to extension alone. It cannot be apprehended by sight, nor by hearing, nor by smell, nor by taste, for it is neither colour, nor sound, nor odour, nor juice. Neither can it be touched, for it is not a body, but it becomes corporeal on being blended with sensible qualities. And, in a later essay, he describes it as receiving all things and letting them depart again without retaining the slightest trace of their presence.483 Why then, it may be asked, if Plotinus meant extension, could he not say so at once, and save us all this trouble in hunting out his meaning? There were very good reasons why he should not. In the first place, he wished to express himself, so far as possible, in Aristotelian phraseology, and this was incompatible with the reduction of Matter to extension. In the next place, the idea of an infinite void had been already appropriated by the Epicureans, to whose system he was bitterly opposed. And, finally, the extension of ordinary327 experience had not the absolute generality which was needed in order to bring Matter into relation with that ultimate abstraction whence, like everything else, it has now to be derived. That the millionaire was genuine, ¡°in person and not a caricature,¡± as Dick put it, was evident. Both the nurse, his relative, and his wife, were chatting with him as Jeff delivered the heavy packed ball made up of the gum. 233 "I guess not," said Landor, tolerantly, as he turned[Pg 106] his horse over to his orderly; "but, anyway," he added to Ellton, "we had a picnic¡ªof a sort." Si, unable to think of anything better, went with him. The train had stopped on a switch, and seemed likely to rust fast to the rails, from the way other trains were going by in both directions. The bridge gang, under charge of a burly, red-faced young Englishman, was in the rear car, with their tools, equipments, bedding and cooking utensils. THE DEACON HAS SOME EXPERIENCES WITH THE QUADRUPED. "You are not within a mile of the truth. I know it. Look here: I believe that is Gen. Rosecrans's own cow. She's gone, and I got an order to look around for her. I've never seen her, but from the description given me I believe that's she. Who brought her here?" "Deacon, these brothers and sisters who have come here with me to-night are, like myself, deeply interested in the moral condition of the army, where we all have sons or kinsmen. Now, can't you sit right there and tell us of your observations and experiences, as a Christian man and father, from day to day, of every day that you were down there? Tell us everything, just as it happened each day, that we may be able to judge for ourselves." HAS AN ENCOUNTER WITH THE PROVOST-MARSHAL. "Wonder which one o' them is the 200th Injianny's?" said Si to Shorty. "And your mother, and Harry?" The daughter must be the girl who was talking to him now. She sat on a little stool by the fire, and had brought out some sewing. "Over at Grandturzel¡ªcan't see wot's burning from here. Git buckets and come!" These things, however, gave little concern to the worthy who commanded the Kentish division. Tyler, though an excellent blacksmith, possessed few of the qualities requisite for forming a good general. Provided there was no very sensible diminution in the number of his followers, he cared not a straw for the score or two who, after quarrelling, or perhaps fighting, withdrew in such disgust that they vowed rather to pay the full tax for ever than submit to the insolence of the rebels. One man could fight as well as another, reasoned he; and, provided he was obeyed, what mattered it by whom. Dick went and Tom came¡ªit was sure to be all one in the end. But this burst of indignation soon passed away, and upon the suggestion of the prudent Sir Robert Hailes, he sent an evasive answer, with a command that the Commons should attend him at Windsor on the Sunday following. That it was a stratagem to gain entrance to the Tower, was the opinion of several, but, after much discussion, it was decided that the man should be admitted, and that the monk should be exhibited merely to intimidate the rebels, until the result of this promised communication should be known. HoMEŮͬÐÔÁµcbcb
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