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Man Pages


Manual Reference Pages  -  BRACKUP::DIGESTCACHE (3)

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NAME

Brackup::DigestCache - cache digests of file and chunk contents

CONTENTS

DESCRIPTION

The brackup DigestCache caches the digests (currently SHA1) of files and file chunks, to prevent untouched files from needing to be re-read on subsequent, iterative backups.

The digest cache is purely a cache. It has no critical data in it, so if you lose it, subsequent backups will just take longer while the digest cache is re-built.

Note that you don’t need the digest cache to do a restore.

DETAILS

    Storage type

The digest cache makes use of Dictionary modules (Brackup::Dict::*) to handle the storage of the cache. The default dictionary used is Brackup::Dict::SQLite, which stores the cache as an SQLite database in a single file. The schema is created automatically as needed... no database maintenance is required.

The dictionary type can be specified in the [SOURCE] declaration in your brackup.conf file, using the ’digestdb_type’ property e.g.:



  [SOURCE:home]
  path = /home/bradfitz/
  # specify the lighter/slower Brackup::Dict::SQLite2 instead of the default
  digestdb_type = SQLite2



    File location

The cache database file is stored in either the location specified in a Brackup::Root’s [SOURCE] declaration in ~/.brackup.conf, as:



  [SOURCE:home]
  path = /home/bradfitz/
  # be explicit if you want:
  digestdb_file = /var/cache/brackup-brad/digest-cache-bradhome.db



Or, more commonly (and recommended), is to not specify it and accept the default location, which is .brackup-digest.db in the root’s root directory.



  [SOURCE:home]
  path = /home/bradfitz/
  # this is the default:
  # digestdb_file = /home/bradfitz/.brackup-digest.db



    Keys & Values stored in the cache

<B>Files digests keysB> (see Brackup::File)



  [rootname]path/to/file.txt:<ctime>,<mtime>,<size>,<inodenum>



<B>Chunk digests keysB> (see Brackup::PositionedChunk)



  [rootname]path/to/file.txt:<ctime>,<mtime>,<size>,<inodenum>;o=<offset>;l=<length>



<B>ValuesB>

In both cases, the values are the digest of the chunk/file, in form:



   sha1:e23c4b5f685e046e7cc50e30e378ab11391e528e



SEE ALSO

brackup

Brackup

Brackup::Dict::SQLite

Brackup::Dict::SQLite2

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perl v5.20.3 BRACKUP::DIGESTCACHE (3) 2010-03-27

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