--
-- The index is stored in an SQLite3 database. This is its schema.
+-- List of snapshots which have been created.
+create table snapshots (
+ snapshotid integer primary key,
+ name text not null,
+ scheme text,
+ timestamp real
+);
+
+-- List of segments which have been created.
+create table segments (
+ segmentid integer primary key,
+ segment text unique not null,
+ path text,
+ checksum text
+);
+
-- Index of all blocks which have been stored in a snapshot, 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,
- timestamp real
+ 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
+ snapshotid integer
);
+create unique index snapshot_contents_unique
+ on snapshot_contents(blockid, snapshotid);
+
+-- Summary statistics for each segment.
+create view segment_info as select * from
+ (select segmentid, max(timestamp) as mtime,
+ sum(size) as size, count(*) as objects
+ from block_index join segments using (segmentid) group by segmentid)
+natural join
+ (select segmentid, sum(size) as used, count(*) as objects_used
+ from block_index where blockid in
+ (select blockid from snapshot_contents) group by segmentid);
+
+-- Ranking of segments to be cleaned, using a benefit function of
+-- (fraction free space)*(age of youngest object).
+create view cleaning_order as select *, (1-u)*age/(u+0.1) as benefit from
+ (select segmentid,
+ cast(used as real) / size as u, julianday('now') - mtime as age
+ from segment_info)
+where benefit > 0;