X-Git-Url: http://git.vrable.net/?p=cumulus.git;a=blobdiff_plain;f=schema.sql;h=fdd888494dd253e9c6e1b7b8679c0e40ee849aef;hp=5017d9bf530461c01a040fe56973674ba3835605;hb=HEAD;hpb=cbcd65669e0040a2a172a1e36d074dc98f118537

diff --git a/schema.sql b/schema.sql
index 5017d9b..fdd8884 100644
--- a/schema.sql
+++ b/schema.sql
@@ -3,54 +3,95 @@
 --
 -- The index is stored in an SQLite3 database.  This is its schema.
 
--- List of snapshots which have been created.
+-- A note on date formats: values which represent timestamps are generally
+-- stored in SQLite's julianday format (Julian day stored as a 64-bit float).
+-- However, application code should allow any value accepted by SQLite's
+-- date/time functions: Julian day or ISO8601 text string.  Code reading from
+-- the database should select julianday(timestamp) or datetime(timestamp),
+-- depending on the desired format for parsing.
+--
+-- Because the julianday format uses floating point, code should not rely on
+-- exact equality tests between timestamps, or precise round-tripping of
+-- timestamp values.
+--
+-- Timestamps are always in UTC.
+
+-- Versioning information, describing the revision for which the table schema
+-- was set up.
+create table schema_version(
+    version text,               -- Program version, dotted decimal string
+    major integer,              -- Major version number
+    minor integer               -- Minor version number
+);
+insert into schema_version values ('0.11', 0, 11);
+
+-- List of snapshots which have been created and which we are still tracking.
+-- There may be more snapshots than this actually stored at the remote server,
+-- but the reverse should not ever be true: Cumulus may depend on data stored
+-- in these snapshots when writing a new snapshot.
 create table snapshots (
     snapshotid integer primary key,
     name text not null,
-    timestamp real
+    scheme text not null,
+    timestamp datetime          -- should match the timestamp of the snapshot
 );
 
 -- List of segments which have been created.
 create table segments (
     segmentid integer primary key,
-    segment text unique not null
+    segment text unique not null,
+    timestamp datetime,         -- when was the segment written?
+    path text,
+    checksum text,
+    data_size integer,          -- sum of bytes in all objects in the segment
+    disk_size integer,          -- size of segment on disk, after compression
+    type text
 );
+create unique index segment_name_index on segments(segment);
 
--- Index of all blocks which have been stored in a snapshot, by checksum.
+-- Index of all data blocks in stored segments.  This is indexed by content
+-- hash to allow for coarse block-level data deduplication.
 create table block_index (
     blockid integer primary key,
     segmentid integer not null,
     object text not null,
     checksum text,
     size integer,
-    timestamp real,
+    timestamp datetime,         -- when a block with this data was first stored
     expired integer
 );
 create index block_content_index on block_index(checksum);
 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,
-    snapshotid integer
+-- 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 [28 bytes if SHA-224]) 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/sha224', which specifies
+-- a target 4 kB block size with parameters set to match LBFS, and SHA-224 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 snapshot.
+create table segment_utilization (
+    snapshotid integer not null,
+    segmentid integer not null,
+
+    -- Estimate for the number of live bytes in data objects: this is capped at
+    -- segments.data_size if all data in the segment is referenced.
+    bytes_referenced integer not null
 );
-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 natural join segments 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 as benefit from
-    (select segmentid,
-            cast(used as real) / size as u, julianday('now') - mtime as age
-        from segment_info)
-where benefit > 0;
+create unique index segment_utilization_index
+    on segment_utilization(snapshotid, segmentid);