4.3 The on-disk cache

The on-disk cache consists in a filesystem subtree rooted at a location defined by the variable diskCacheRoot, by default "/var/cache/polipo/". This directory should normally be writeable, readable and seekable by the user running Polipo. While it is best to use a local filesystem for the on-disk cache, a NFSv3- or AFS-mounted filesystem should be safe in most implementations. Do not use NFSv2, as it will cause cache corruption ¹³.

If diskCacheRoot is an empty string, no disk cache is used.

The value maxDiskEntries (32 by default) is the absolute maximum of file descriptors held open for on-disk objects. When this limit is reached, Polipo will close descriptors on a least-recently-used basis. This value should be set to be slightly larger than the number of resources that you expect to be live at a single time; defining the right notion of liveness is left as an exercise for the interested reader.

The value diskCacheWriteoutOnClose (64kB by default) is the amount of data that Polipo will write out when closing a disk file. Writing out data when closing a file can avoid subsequently reopening it, but causes unnecessary work if the instance is later superseded.

The integers diskCacheDirectoryPermissions and diskCacheFilePermissions are the Unix filesystem permissions with which files and directories are created in the on-disk cache; they default to ‘0700’ and ‘0600’ respectively.

The variable maxDiskCacheEntrySize specifies the maximum size, in bytes, of an instance that is stored in the on-disk cache. If set to -1 (the default), all objects are stored in the on-disk cache,