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Brackup::InventoryDataUser(Contributed Perl DocumBrackup::InventoryDatabase(3)

NAME
       Brackup::InventoryDatabase - track what chunks are already on a target

DESCRIPTION
       The Brackup InventoryDatabase keeps track of which chunks (files) are
       already on a given target, speeding up future iterative backups,
       negating	the need to ask	the target for each chunk whether it exists or
       not (which may be a lot of network roundtrips, slow even	in the best of
       network conditions).

       Unlike the Digest Cache,	the inventory database is not a	cache... its
       contents	matter.	 Consider what happens when the	inventory database
       doesn't match reality:

       1) Exists in inventory database;	not on target
	   If a	chunk exists in	the inventory database,	but not	on the target,
	   brackup won't store it on the target, and you'll think a backup
	   succeeded, but it's not actually there.

       2a) Exists on target; not in inventory database (without	encryption)
	   You re-upload it to the target, so you waste	time & bandwidth, but
	   no extra disk space is wasted, and no chunks	are orphaned.
	   Actually, chunks are	un-orphaned, as	the inventory database is now
	   updated and contains	the chunk you just uploaded.

       2b) Exists on target; not in inventory database (with encryption)
	   When	using encryption, each time a chunk is encrypted with gpg, the
	   contents are	different.  So if the inventory	database says a	given
	   chunk isn't already stored on the server, it	will be	re-encrypted
	   and stored (uploaded) again.	 You may or may	not have an orphaned
	   chunk on the	server,	depending on whether or	not it's referenced by
	   any other *.brackup meta files.

       For those reasons, it's somewhat	important that your inventory database
       be kept around and not deleted.	If you're running brackup to the same
       target from different computers,	you might want to sync up your
       inventory databases with	each other, so you don't do unnecessary
       uploads to the target.

       Tools to	rebuild	your inventory database	from the target's enumeration
       of its chunks and the target's *.brackup	metafiles isn't	yet done, but
       would be	pretty easy.  (this is a TODO item)

       In any case, it's not tragic if you lose	your inventory database... it
       just means you'll need to upload	more stuff and maybe waste some	disk
       space until you next run	a 'brackup-target gc' garbage collection,
       which cleans up orphaned	chunks.	If you're feeling paranoid, it's safer
       to delete your inventory	database, tricking Brackup into	thinking your
       target is empty (even if	it's not), rather than Brackup thinking	your
       target has something when it actually doesn't.

DETAILS
   Storage type
       The inventory database makes use	of Dictionary modules
       (Brackup::Dict::*) to handle database storage. 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 [TARGET] declaration	in
       your brackup.conf file, using the 'inventorydb_type' property e.g.:

	 [TARGET:amazon]
	 type =	Amazon
	 aws_access_key_id  = ...
	 aws_secret_access_key =  ...
	 # specify the lighter/slower Brackup::Dict::SQLite2 instead of	the default
	 inventorydb_type = SQLite2

   File	location
       The inventory database file (for	file-based dictionaries) is stored in
       either the location specified in	the 'inventorydb_file' property	of a
       [TARGET]	declaration in ~/.brackup.conf e.g.:

	 [TARGET:amazon]
	 type =	Amazon
	 aws_access_key_id  = ...
	 aws_secret_access_key =  ...
	 inventorydb_file = /home/bradfitz/.amazon-already-has-these-chunks.db

       Or, more	commonly (and recommended), is to not specify it and accept
       the default location, which is ".brackup-target-TARGETNAME.invdb" in
       your home directory (where it might be shared by	multiple backup
       roots).

   SQLite Schema
       This is made automatically for you, but if you want to look around in
       it, the schema is:

	 CREATE	TABLE target_inv (
	      key TEXT PRIMARY KEY,
	      value TEXT
	 )

   Keys	& Values stored	in the database
       Keys

       The key is the digest of	the "raw" (pre-compression/encryption)
       file/chunk (with	GPG recipient, if using	encryption), and the value is
       the digest of the chunk stored on the target, which contains the	raw
       chunk.  The chunk stored	on the target may contain other	chunks,	may be
       compressed, encrypted, etc.

	<raw_digest>		   --> <stored_digest> <stored_length>
	<raw_digest>;to=<gpg_rcpt> --> <stored_digest> <stored_length>

       For example:

	 sha1:e23c4b5f685e046e7cc50e30e378ab11391e528e;to=6BAFF35F =>
	    sha1:d7257184899c9e6c4e26506f1c46f8b6562d9ee7 71223

       Means that the chunk with sha1 contents "e23c4...", intended to be
       en/de-crypted for 6BAFF35F, can be got by asking	the target for the
       chunk with digest "d72571848...", with length 71,223 bytes.

       When using the Brackup feature which combines small files into larger
       blobs, the inventory database instead stores values like:

	 <raw_digest>[;to=<gpg_rcpt>] -->
	    <stored_digest> <stored_length> <from_offset>-<to_offset>

       Which is	the same thing,	but after fetching the composite chunk using
       the stored digest provided, only	the range provided from	"from_offset"
       to "to_offset" should be	used.

SEE ALSO
       Brackup

       Brackup::Target

perl v5.32.1			  2010-03-27	 Brackup::InventoryDatabase(3)

NAME | DESCRIPTION | DETAILS | SEE ALSO

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