The map::at method does not always exist, so instead use map::find.

[cumulus.git] / schema.sql

diff --git a/schema.sql b/schema.sql
index 096069b..35b2c9d 100644 (file)
--- a/schema.sql
+++ b/schema.sql
@@ -3,20 +3,74 @@
 --
 -- 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,
-    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
+-- 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);