storage

doc/sphinx/users-guide/storage-backends.rst

 
-
 Storage backends
 ----------------
 
+
 Intro
 ~~~~~
 
-Varnish has pluggable storage backends. It can store data in various
-backends which have different performance characteristics.
+When you configure Varnish you need to give it some place to store
+data. Varnish has pluggable storage backends. It can store data in
+various backends which have different characteristics with regards to
+semantics and performance.
+
+malloc
+~~~~~~
+
+syntax: malloc[,size]
+
+Malloc is a memory based backend. Each object will be allocated from
+memory. If your system runs low on memory swap will be used. Be aware
+that the size limitation only limits the actual storage and that
+approximately 1k of memory per object will be used for various
+internal structures.
+
+The size parameter specifies the maximum amount of memory varnishd
+will allocate.  The size is assumed to be in bytes, unless followed by
+one of the following suffixes:
+
+      K, k    The size is expressed in kibibytes.
+
+      M, m    The size is expressed in mebibytes.
+
+      G, g    The size is expressed in gibibytes.
+
+      T, t    The size is expressed in tebibytes.
+
+The default size is unlimited. 
+
+Mallocs performance is bound by memory speed so it is very fast. If
+the dataset is bigger than what can fit in memory performance will
+depend on the operating system and how well it doesn paging. 
+
+file
+~~~~
+
+syntax: file[,path[,size[,granularity]]]
+
+The file backend stores objects in memory backed by a file on disk
+with mmap. This is the default storage backend and unless you specify
+another storage this one will used along with Transient storage.
+
+The path parameter specifies either the path to the backing file or
+the path to a directory in which varnishd will create the backing
+file.  The default is /tmp.
+
+The size parameter specifies the size of the backing file.  The size
+is assumed to be in bytes, unless followed by one of the following
+suffixes:
+
+      K, k    The size is expressed in kibibytes.
+
+      M, m    The size is expressed in mebibytes.
+
+      G, g    The size is expressed in gibibytes.
+
+      T, t    The size is expressed in tebibytes.
+
+      %       The size is expressed as a percentage of the free space on the
+              file system where it resides.
+
+The default size is 50%.
+
+If the backing file already exists, it will be truncated or expanded
+to the specified size.
+
+Note that if varnishd has to create or expand the file, it will not
+pre-allocate the added space, leading to fragmentation, which may
+adversely impact performance on rotating hard drives.  Pre-creating
+the storage file using dd(1) will reduce fragmentation to a minimum.
+
+The granularity parameter specifies the granularity of
+allocation.  All allocations are rounded up to this size.  The
+is assumed to be in bytes, unless followed by one of the
+suffixes described for size except for %.
+
+The default size is the VM page size.  The size should be reduced if
+you have many small objects.
+
+File performance is typically limited by the write speed of the
+device, and depending on use, the seek time.
+
+persistent (experimental)
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+syntax: persistent,path,size {experimental}
+
+Persistent storage. Varnish will store objects in a file in a manner
+that will secure the survival of *most* of the objects in the event of
+a planned or unplanned shutdown of Varnish.
+
+The path parameter specifies the path to the backing file. If
+the file doesn't exist Varnish will create it.
+
+The size parameter specifies the size of the backing file.  The
+size is assumed to be in bytes, unless followed by one of the
+following suffixes:
+
+      K, k    The size is expressed in kibibytes.
+
+      M, m    The size is expressed in mebibytes.
+
+      G, g    The size is expressed in gibibytes.
+
+      T, t    The size is expressed in tebibytes.
+
+Varnish will split the file into logical *silos* and write to the
+silos in the manner of a circular buffer. Only one silo will be kept
+open at any given point in time. Full silos are *sealed*. When Varnish
+starts after a shutdown it will discard the content of any silo that
+isn't sealed.
 
-.. include:: ../include/storage_backends.rst
+Transient Storage
+-----------------
+      
+If you name any of your storage backend "Transient" it will be
+used for transient (short lived) objects. By default Varnish
+would use an unlimited malloc backend for this.