Rewrite TODO.md sentence by sentence (closes #135)

Rewrites `TODO.md` from scratch for
#135, by the rules applied to
`README.md` in #140. It is the
project's own task list, so every completed step keeps its date, its
issue or branch and every fact that the old entry recorded, in short
sentences, with lists as bullets. An entry superseded later says so in
one sentence.

`TODO.md` records history, so its entries were not corrected against the
code. The 2026-10-17 release-rule entry is known to be stale. One product
name in the 2026-10-15 entry is replaced by a description.

This file carries the `TODO.md` entry of
#140 word for word, so the
conflict once that merges is resolved by taking this file whole.

Model: fable-5-1

README.md

@@ -393,20 +393,6 @@ All four subcommands operate on a single SQLite database file:
         content    BLOB NOT NULL      -- raw 32-byte SHA-256; whole file under 100 MiB, else samples
     ) WITHOUT ROWID;
     CREATE INDEX files_signature ON files (size, head, tail, content);
-    CREATE TABLE totals (
-        records INTEGER NOT NULL,  -- number of records in files
-        size    INTEGER NOT NULL   -- sizes of all records in files added up
-    );
-    INSERT INTO totals (records, size) VALUES (0, 0);
-    CREATE TRIGGER totals_after_insert AFTER INSERT ON files BEGIN
-        UPDATE totals SET records = records + 1, size = size + NEW.size;
-    END;
-    CREATE TRIGGER totals_after_delete AFTER DELETE ON files BEGIN
-        UPDATE totals SET records = records - 1, size = size - OLD.size;
-    END;
-    CREATE TRIGGER totals_after_update AFTER UPDATE OF size ON files BEGIN
-        UPDATE totals SET size = size + NEW.size - OLD.size;
-    END;
     ```
 
     Paths are stored as BLOBs because Unix paths are raw bytes, not guaranteed
@@ -420,13 +406,6 @@ All four subcommands operate on a single SQLite database file:
     `files_signature` index lets `report` read the records in signature order
     without sorting the table.
 
-    `totals` holds one row: the number of records in `files` and the sum of
-    their sizes. Its three triggers keep that row current. Each runs in the
-    transaction of the change to `files` that fires it, so the row and the
-    records always agree. `info` and the progress displays read the number of
-    records from this row. Counting them in `files` would read every record,
-    which takes minutes on a database of tens of millions.
-
 ### Duplicate detection
 
 Two files are duplicates when they have the same size and the same three hashes.
@@ -709,14 +688,14 @@ Processing:
   database state.
 
 `report` runs in two phases, each with its own progress display on stderr (see
-"Progress"): `open` opens the database; `read` gets the number of records from
+"Progress"): `open` opens the database; `read` counts the records, then reads
-`totals`, then reads the records in signature order, largest size first. That is
+them in signature order, largest size first. That is the order of the
-the order of the `files_signature` index read backwards, so SQLite sorts nothing
+`files_signature` index read backwards, so SQLite sorts nothing and returns the
-and returns the first record at once. The records sharing a signature come
+first record at once. The records sharing a signature come together, and so do
-together, and so do the records of one size, so `report` holds only the
+the records of one size, so `report` holds only the duplicate groups of the size
-duplicate groups of the size it is reading, and writes them, ordered by `first`
+it is reading, and writes them, ordered by `first` path, once it reaches a
-path, once it reaches a smaller size. Its memory holds at most the duplicate
+smaller size. Its memory holds at most the duplicate paths of one size at a
-paths of one size at a time, never every record.
+time, never every record.
 
 #### Report output format
 
@@ -790,10 +769,10 @@ Processing:
   ascending. Output must be fully deterministic for a given input.
 
 `trees` runs in four phases, each with its own progress display on stderr (see
-"Progress"): `open` opens the database; `read` gets the number of records from
+"Progress"): `open` opens the database; `read` counts the records, then reads
-`totals`, then reads the records in path order, building the hierarchy and
+them in path order, building the hierarchy and computing the digests as it goes;
-computing the digests as it goes; `group` groups the directories by digest and
+`group` groups the directories by digest and picks the maximal groups; `write`
-picks the maximal groups; `write` writes the groups to stdout.
+writes the groups to stdout.
 
 #### Trees output format
 
@@ -844,10 +823,11 @@ size of recorded files	150000000000000 (136.4 TiB)
   of all records, in bytes, then in human units.
 
 `info` runs in two phases, each with its own progress display on stderr (see
-"Progress"): `open` opens the database; `count` reads the schema version and the
+"Progress"): `open` opens the database; `count` reads the schema version and
-row of `totals` (see "Database") in one read-only transaction, so the numbers
+counts the records with one query, a single pass over the table, both in one
-agree with each other while a scan is committing. `info` writes its lines once
+read-only transaction, so the numbers agree with each other while a scan is
-the `count` display has ended, so on a terminal they come after the displays.
+committing. `info` writes its lines once the `count` display has ended, so on a
+terminal they come after the displays.
 
 ### Progress
 
@@ -863,9 +843,8 @@ progress, its elapsed time and its time remaining.
 A scan has four phases (`[1/4] load`, `[2/4] walk`, `[3/4] hash`,
 `[4/4] update`):
 
-- `load` gets the number of records from `totals` first, then reads the records
+- `load` counts the records first, then reads them against that count. While the
-  against that number. Until it has the number, the display says it is counting
+  count runs, the display says it is counting the records.
-  the records.
 - `walk` has no exact total. Its estimate is the number of records the last scan
   left under the operands, known once `load` is done and shown with a `~`. The
   time remaining is unknown once the walk passes the estimate, and when there
@@ -878,9 +857,8 @@ A scan has four phases (`[1/4] load`, `[2/4] walk`, `[3/4] hash`,
 
 - `open` has no total. While it opens the database, waiting on a busy one
   included, the display says it is opening the database.
-- `read` gets the number of records from `totals` first, then reads the records
+- `read` counts the records first, then reads them against that count. While the
-  against that number. Until it has the number, the display says it is counting
+  count runs, the display says it is counting the records.
-  the records.
 - `group` has the directories `read` found as its total, and `write` the
   duplicate-tree groups.
 
@@ -888,16 +866,17 @@ A scan has four phases (`[1/4] load`, `[2/4] walk`, `[3/4] hash`,
 
 - `open` has no total. While it opens the database, waiting on a busy one
   included, the display says it is opening the database.
-- `read` gets the number of records from `totals` first, then reads the records
+- `read` counts the records first, then reads them against that count, writing
-  against that number, writing the rows to stdout as it goes. Until it has the
+  the rows to stdout as it goes. While the count runs, the display says it is
-  number, the display says it is counting the records.
+  counting the records.
 
 `info` has two phases (`[1/2] open`, `[2/2] count`, see "`info` mode"):
 
 - `open` has no total. While it opens the database, waiting on a busy one
   included, the display says it is opening the database.
-- `count` has no total either, because it reads one row: the display says it is
+- `count` has no total either, because one query counts everything: the display
-  counting the records until it has the row, and its time remaining is unknown.
+  says it is counting the records until the query returns, and its time
+  remaining is unknown.
 
 Each display is one line holding:
 

db.go

@@ -69,49 +69,6 @@ const createIndexSQL = `
 CREATE INDEX files_signature ON files (size, head, tail, content)
 `
 
-// createTotalsSQL creates the totals table, which holds one row: the
-// number of records and the sizes of all records added up. Counting
-// them over files would read every record. The three triggers below
-// keep the row current, in the transaction of each change to files.
-const createTotalsSQL = `
-CREATE TABLE totals (
-    records INTEGER NOT NULL,
-    size    INTEGER NOT NULL
-)
-`
-
-// insertTotalsSQL adds the one row of totals, for an empty files table.
-const insertTotalsSQL = `
-INSERT INTO totals (records, size) VALUES (0, 0)
-`
-
-// totalsAfterInsertSQL counts each inserted record into totals.
-const totalsAfterInsertSQL = `
-CREATE TRIGGER totals_after_insert AFTER INSERT ON files BEGIN
-    UPDATE totals SET records = records + 1, size = size + NEW.size;
-END
-`
-
-// totalsAfterDeleteSQL takes each deleted record out of totals.
-const totalsAfterDeleteSQL = `
-CREATE TRIGGER totals_after_delete AFTER DELETE ON files BEGIN
-    UPDATE totals SET records = records - 1, size = size - OLD.size;
-END
-`
-
-// totalsAfterUpdateSQL replaces a record's old size in totals with its
-// new one. scan's upsert of an existing record is such an update.
-const totalsAfterUpdateSQL = `
-CREATE TRIGGER totals_after_update AFTER UPDATE OF size ON files BEGIN
-    UPDATE totals SET size = size + NEW.size - OLD.size;
-END
-`
-
-// recordCountSQL reads the number of records from totals.
-const recordCountSQL = `
-SELECT records FROM totals
-`
-
 // upsertSQL inserts one file record, replacing any existing record for
 // the same path.
 const upsertSQL = `
@@ -469,14 +426,14 @@ func createSchema(ctx context.Context, db *sql.DB) error {
 
 	defer func() { _ = tx.Rollback() }()
 
-	for _, stmt := range []string{
+	_, err = tx.ExecContext(ctx, createTableSQL)
-		createTableSQL, createIndexSQL, createTotalsSQL, insertTotalsSQL,
+	if err != nil {
-		totalsAfterInsertSQL, totalsAfterDeleteSQL, totalsAfterUpdateSQL,
+		return fmt.Errorf("create schema: %w", err)
-	} {
+	}
-		_, err = tx.ExecContext(ctx, stmt)
+
-		if err != nil {
+	_, err = tx.ExecContext(ctx, createIndexSQL)
-			return fmt.Errorf("create schema: %w", err)
+	if err != nil {
-		}
+		return fmt.Errorf("create schema: %w", err)
 	}
 
 	_, err = tx.ExecContext(ctx,
@@ -523,7 +480,7 @@ func loadFileRows(ctx context.Context, db *sql.DB, total func(n int64),
 
 	var n int64
 
-	err = tx.QueryRowContext(ctx, recordCountSQL).Scan(&n)
+	err = tx.QueryRowContext(ctx, "SELECT COUNT(*) FROM files").Scan(&n)
 	if err != nil {
 		return fmt.Errorf("count records: %w", err)
 	}
@@ -599,7 +556,7 @@ func loadSignatureRows(ctx context.Context, db *sql.DB,
 
 	var n int64
 
-	err = tx.QueryRowContext(ctx, recordCountSQL).Scan(&n)
+	err = tx.QueryRowContext(ctx, "SELECT COUNT(*) FROM files").Scan(&n)
 	if err != nil {
 		return fmt.Errorf("count records: %w", err)
 	}
@@ -665,7 +622,7 @@ func (r *scanRec) setHashes(head, tail, content []byte) error {
 func countRecords(ctx context.Context, db *sql.DB) (int64, error) {
 	var n int64
 
-	err := db.QueryRowContext(ctx, recordCountSQL).Scan(&n)
+	err := db.QueryRowContext(ctx, "SELECT COUNT(*) FROM files").Scan(&n)
 	if err != nil {
 		return 0, fmt.Errorf("count records: %w", err)
 	}
@@ -673,10 +630,12 @@ func countRecords(ctx context.Context, db *sql.DB) (int64, error) {
 	return n, nil
 }
 
-// databaseCountsSQL reads the number of records and the sizes of all
+// databaseCountsSQL counts the records and adds up their sizes, in one
-// records added up from totals.
+// pass over the table. A SUM over no rows is NULL, so on an empty table
+// the SUM falls back to 0.
 const databaseCountsSQL = `
-SELECT records, size FROM totals
+SELECT COUNT(*), COALESCE(SUM(size), 0)
+FROM files
 `
 
 // databaseCounts is what info reads from the database: its schema

db_test.go

@@ -535,12 +535,17 @@ func TestLoadRowsRefuseWrongSizeHash(t *testing.T) {
 	}
 }
 
-// queryPlan returns the detail of each line of SQLite's EXPLAIN QUERY
+// TestSignatureRowsNeedNoSort checks that SQLite reads signatureRowsSQL
-// PLAN for query.
+// from the files_signature index alone, with nothing to sort: the
-func queryPlan(t *testing.T, db *sql.DB, query string) []string {
+// first record comes at once, so report's read phase counts each
-	t.Helper()
+// record as it comes rather than waiting on SQLite for all of them.
+func TestSignatureRowsNeedNoSort(t *testing.T) {
+	t.Parallel()
 
-	rows, err := db.QueryContext(t.Context(), "EXPLAIN QUERY PLAN "+query)
+	db := openTestDB(t)
+
+	rows, err := db.QueryContext(t.Context(),
+		"EXPLAIN QUERY PLAN "+signatureRowsSQL)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -568,105 +573,12 @@ func queryPlan(t *testing.T, db *sql.DB, query string) []string {
 		t.Fatal(err)
 	}
 
-	return plan
-}
-
-// TestSignatureRowsNeedNoSort checks that SQLite reads signatureRowsSQL
-// from the files_signature index alone, with nothing to sort: the
-// first record comes at once, so report's read phase counts each
-// record as it comes rather than waiting on SQLite for all of them.
-func TestSignatureRowsNeedNoSort(t *testing.T) {
-	t.Parallel()
-
-	db := openTestDB(t)
-
-	plan := queryPlan(t, db, signatureRowsSQL)
-
 	want := []string{"SCAN files USING COVERING INDEX files_signature"}
 	if !slices.Equal(plan, want) {
 		t.Errorf("query plan = %q, want %q", plan, want)
 	}
 }
 
-// TestCountsReadOnlyTotals checks that SQLite answers each query that
-// counts the records from the one row of totals. A plan that reads
-// files or its index reads every record.
-func TestCountsReadOnlyTotals(t *testing.T) {
-	t.Parallel()
-
-	db := openTestDB(t)
-
-	for _, query := range []string{recordCountSQL, databaseCountsSQL} {
-		plan := queryPlan(t, db, query)
-
-		want := []string{"SCAN totals"}
-		if !slices.Equal(plan, want) {
-			t.Errorf("query plan of %q = %q, want %q", query, plan, want)
-		}
-	}
-}
-
-// assertTotalsMatchFiles fails unless the row of totals holds the
-// number of records and the sizes of all records added up, as counted
-// over files.
-func assertTotalsMatchFiles(t *testing.T, db *sql.DB) {
-	t.Helper()
-
-	got, err := readDatabaseCounts(t.Context(), db)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	var records, size int64
-
-	err = db.QueryRowContext(t.Context(),
-		"SELECT COUNT(*), COALESCE(SUM(size), 0) FROM files").
-		Scan(&records, &size)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	if got.records != records || got.size != size {
-		t.Errorf("totals = %d records of %d bytes, files holds %d of %d",
-			got.records, got.size, records, size)
-	}
-}
-
-// TestTotalsMatchFiles scans the smoke tree, rescans it after two files
-// change size, and rescans it after two files are removed. After each
-// scan the row of totals must agree with files.
-func TestTotalsMatchFiles(t *testing.T) {
-	t.Parallel()
-
-	dir := buildSmokeTree(t)
-	db := openTestDB(t)
-
-	syncTree(t, db, dir)
-	assertTotalsMatchFiles(t, db)
-
-	writeFile(t, dir, "a/one.bin", pattern(10, 2500))
-	writeFile(t, dir, "t1/f1", pattern(30, 1000))
-
-	if st := syncTree(t, db, dir); st.updated != 2 {
-		t.Fatalf("rescan stats = %+v, want 2 updated", st)
-	}
-
-	assertTotalsMatchFiles(t, db)
-
-	for _, name := range []string{"a/unique.bin", "t2/sub/f2"} {
-		err := os.Remove(filepath.Join(dir, name))
-		if err != nil {
-			t.Fatal(err)
-		}
-	}
-
-	if st := syncTree(t, db, dir); st.removed != 2 {
-		t.Fatalf("rescan stats = %+v, want 2 removed", st)
-	}
-
-	assertTotalsMatchFiles(t, db)
-}
-
 func TestApplyChangesRoundTrip(t *testing.T) {
 	t.Parallel()
 

info.go

@@ -26,11 +26,11 @@ func infoPhase(name string) string {
 // it. Any database problem, including a missing database, is fatal.
 //
 // The work runs in two phases, each under a progress display of its
-// own on stderr: open (open the database) and count (read the number of
+// own on stderr: open (open the database) and count (count the records,
-// records and their total size from the totals table). Each display
+// with one query). Each display ends before the next phase starts, and
-// ends before the next phase starts, and before an error is returned
+// before an error is returned to be printed. The details are written
-// to be printed. The details are written once the last display has
+// once the last display has ended, so no display is drawn while they
-// ended, so no display is drawn while they are written.
+// are written.
 func runInfo(ctx context.Context, stdout io.Writer) error {
 	dbPath, source, err := databasePath()
 	if err != nil {
@@ -56,7 +56,7 @@ func runInfo(ctx context.Context, stdout io.Writer) error {
 
 	defer func() { _ = db.Close() }()
 
-	// One row holds both counts, so the phase never has a total.
+	// One query counts everything, so the phase never has a total.
 	prog = newProgress(progressParams{
 		label: infoPhase("count"), total: -1,
 		waitingFor: countingRecords,

main_test.go

@@ -180,9 +180,9 @@ func capture(t *testing.T, std **os.File) func() string {
 }
 
 // brokenDatabase writes a database that opens cleanly and passes the
-// schema-version check but has no tables, so the first query fails
+// schema-version check but has no files table, so the first query
-// with the database already open: a fatal error on a path that owns an
+// fails with the database already open: a fatal error on a path that
-// open database. It closes the database the way scan does.
+// owns an open database. It closes the database the way scan does.
 func brokenDatabase(t *testing.T) string {
 	t.Helper()
 
@@ -265,9 +265,8 @@ func TestRunFatalAfterOpenClosesDatabase(t *testing.T) {
 			assertFatalOutput(t, stderr.String(), stdout())
 
 			// Proof that the failure happened after the open: only a
-			// query against the opened database can report this. Each
+			// query against the opened database can report this.
-			// subcommand's first query reads totals.
+			if !strings.Contains(stderr.String(), "no such table: files") {
-			if !strings.Contains(stderr.String(), "no such table: totals") {
 				t.Errorf("stderr = %q, want the failure to come from a "+
 					"query on the open database", stderr.String())
 			}

scan.go

@@ -455,8 +455,8 @@ func (s *scanState) walkableRoots(roots []string, rules walkRules) []string {
 // included, so its display counts against the number of records.
 func (s *scanState) loadIndex(ctx context.Context, roots []string) error {
 	// Indexing tens of millions of records takes real time; without a
-	// display the scan looks hung before the walk begins. The number of
+	// display the scan looks hung before the walk begins. Counting them
-	// records, read first, gives the display its total.
+	// first gives the display its total.
 	prog := newProgress(progressParams{
 		label: scanPhase("load"), unit: scanUnit, total: -1,
 		waitingFor: countingRecords, stalledOn: "db",