--
-- The index is stored in an SQLite3 database. This is its schema.
--- Index of all blocks which have been stored in a snapshot, by checksum.
+-- List of snapshots which have been created.
+create table snapshots (
+ snapshotid integer primary key,
+ name text not null,
+ scheme text not null,
+ timestamp real,
+ intent real
+);
+
+-- List of segments which have been created.
+create table segments (
+ segmentid integer primary key,
+ segment text unique not null,
+ path text,
+ checksum text,
+ mtime real,
+ size integer,
+ expire_time integer -- snapshotid of latest snapshot when expired
+);
+
+-- Index of all blocks which have been stored, by checksum.
create table block_index (
blockid integer primary key,
- segment text,
- object text,
+ segmentid integer not null,
+ object text not null,
checksum text,
- size integer
+ size integer,
+ timestamp real,
+ expired integer
);
create index block_content_index on block_index(checksum);
-create index block_name_index on block_index(segment, object);
+create unique index block_name_index on block_index(segmentid, object);
--- Index tracking which blocks are used by which snapshots.
-create table snapshot_contents (
- blockid integer,
- snapshot text
+-- Checksums for the decomposition of blocks into even smaller chunks
+-- (variable-sized, but generally ~4 kB, and maximum 64 kB). Chunk boundaries
+-- are determined based on the contents using Rabin fingerprints. These
+-- checksums can be used for computing sub-file incrementals.
+--
+-- Each block stored in block_index may have an entry in the
+-- subblock_signatures table. The signatures field is a binary blob consisting
+-- of a packed sequence of (chunk length [16-bit unsigned, big-endian],
+-- checksum [20 bytes if SHA-1]) tuples that should cover the entire block.
+--
+-- algorithm specifies the method used for computing break points as well as
+-- the hash function used, so that signatures can be discarded if the algorithm
+-- changes. The current algorithm used is 'lbfs-4096/sha1', which specifies a
+-- target 4 kB block size with parameters set to match LBFS, and SHA-1 as the
+-- hash algorithm.
+create table subblock_signatures (
+ blockid integer primary key,
+ algorithm text not null,
+ signatures blob not null
);
+
+-- Summary of segment utilization for each snapshots.
+create table segments_used (
+ snapshotid integer not null,
+ segmentid integer not null,
+ utilization real
+);
+create unique index segments_used_index
+ on segments_used(snapshotid, segmentid);
+
+-- Overall estimate of segment utilization, for all snapshots combined.
+create view segment_info as
+select segmentid, mtime, size, expire_time,
+ cast(size * utilization as integer) as used, utilization
+from segments join
+ (select segmentid, max(utilization) as utilization
+ from segments_used group by segmentid)
+using (segmentid);