Keep the database schema at version 1 (closes #61)

sfdupes is pre-1.0, with no installed base and no databases anywhere,
so the schema is changed in place and its version stays 1.
schemaVersion goes back to 1; the six-column files table, content
included, is the version 1 schema. The check that stops on a database
with any other version stays. README.md and TODO.md no longer describe
a version 2 or rejecting and rescanning version 1 databases. The
main.go package comment still described 1024-byte end windows and said
full file contents are never read; it now describes the hashes the
code computes.

Model: opus-5-5

README.md

@@ -154,11 +154,8 @@ All three subcommands operate on a single SQLite database file:
     that dies partway leaves a valid database holding everything
     hashed so far; the next scan skips those records and converges
     toward the filesystem.
--   Schema (`PRAGMA user_version` is the schema version, currently 2; a
+-   Schema (`PRAGMA user_version` is the schema version, currently 1; a
-    database with any other version is a fatal error). Version 2 added
+    database with any other version is a fatal error):
-    the `content` column and the 64 KiB head/tail signature (replacing
-    the version 1 1 KiB end windows), so a version 1 database cannot be
-    reused: it is rejected and the tree must be rescanned from scratch.
 
     ```sql
     CREATE TABLE files (

TODO.md

@@ -36,12 +36,11 @@
   `head`, `tail`, and `content` all hold the whole-file hash. A file at
   10 MiB or above is gated on the 64 KiB `head` and `tail`, then
   compared on a `content` hash — the whole file below 50 MiB,
-  gigabyte-spaced 1 MiB samples at or above. Schema bumps to version 2
+  gigabyte-spaced 1 MiB samples at or above. The `content` column is
-  (new `content` column); a version 1 database is rejected and must be
+  part of the version 1 schema. `report` and `trees` group by the
-  rescanned, which is required anyway since every stored hash changed.
+  extended signature, so the ladder is applied across the whole
-  `report` and `trees` group by the extended signature, so the ladder is
+  database. README "Duplicate detection" documents every rung including
-  applied across the whole database. README "Duplicate detection"
+  the probabilistic large-file path.
-  documents every rung including the probabilistic large-file path.
 
 - remove the dead `files.dat` references from `Makefile`, `.gitignore`
   and `.dockerignore` (2026-09-21, branch `next`, closes

db.go

@@ -25,11 +25,8 @@ const defaultDatabasePath = "/var/lib/sfdupes/db.sqlite"
 const databaseEnv = "SFDUPES_DATABASE"
 
 // schemaVersion is the database schema version this build reads and
-// writes, stored in PRAGMA user_version. Version 2 adds the content
+// writes, stored in PRAGMA user_version.
-// column and the head/tail/content signature (replacing the version 1
+const schemaVersion = 1
-// 1 KiB end windows), so a version 1 database is rejected and must be
-// rescanned.
-const schemaVersion = 2
 
 // dbDirPerm is the mode for a database parent directory created by
 // scan.

main.go

@@ -1,10 +1,13 @@
 // Command sfdupes quickly identifies candidate duplicate files across
-// very large filesystems without reading full file contents. Files are
+// very large filesystems without reading every byte of every file.
-// considered duplicates when they have identical size, identical SHA-256
+// Files are considered duplicates when their sizes are equal and they
-// of their first 1024 bytes, and identical SHA-256 of their last 1024
+// agree on a short ladder of SHA-256 hashes. A file under 10 MiB is
-// bytes. scan maintains a persistent SQLite database of file signatures
+// hashed in full. A larger file is compared on the hashes of its first
-// (SFDUPES_DATABASE, default /var/lib/sfdupes/db.sqlite) that the
+// and last 64 KiB and on a content hash: of the whole file when it is
-// reporting subcommands read.
+// under 50 MiB, or of gigabyte-spaced 1 MiB samples when it is 50 MiB
+// or larger. scan maintains a persistent SQLite database of file
+// signatures (SFDUPES_DATABASE, default /var/lib/sfdupes/db.sqlite)
+// that the reporting subcommands read.
 //
 // Usage:
 //