-- We maintain a local index of data blocks that have been previously stored
-- for constructing incremental snapshots.
--
-- 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,
    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,
    segmentid integer not null,
    object text not null,
    checksum text,
    size integer,
    timestamp real,
    expired integer
);
create index block_content_index on block_index(checksum);
create unique index block_name_index on block_index(segmentid, object);

-- 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, 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);
