README.md

@@ -142,7 +142,16 @@ and origin AS can have two kept routes, one or none.
 - `/prefix/{prefix}/{length}`: a prefix, such as `/prefix/192.0.2.0/24`, with
   its origin ASes and every peer that carries it. Only the kept routes show an
   AS path, a next hop and a time. The next hop is the router the peer sends the
-  prefix's traffic to. RouteWatch records the peer itself as the next hop.
+  prefix's traffic to. RouteWatch records the peer itself as the next hop. The
+  page also lists the prefix's origin changes, newest first. An origin change is
+  an AS starting to announce the prefix, when its first peer carries it, or
+  stopping, when its last peer no longer does. The page shows at most the newest
+  5,000. Each row shows:
+    - the time
+    - announced or withdrawn
+    - the origin AS
+    - the peer count: how many peers carry the prefix just after the change,
+      with any origin AS
 - `/prefixlength/{length}`: up to 500 IPv4 prefixes with that mask length,
   picked at random. Each shows its origin AS and the age of its newest kept
   route. When peers give a prefix different origin ASes, the page shows the one
@@ -516,7 +525,8 @@ The ceilings add up to 3.7 GiB:
   pairs, so it takes about 1 GB. The rest of the heap takes up to about 0.5 GiB,
   most of it the handlers' batches and queues (see below). The remaining 1 GiB
   is room for the garbage collector, which frees memory the program no longer
-  uses. With much less, it would run almost all the time.
+  uses. With much less, it would run almost all the time. The routing table also
+  keeps at most 100,000 origin changes waiting to be written, about 8 MB.
 - SQLite: 1 GiB, set in the code. The connection that does every write has a 512
   MiB page cache: the database pages it keeps in memory from one write to the
   next. The `routes` table of a full routing table takes about 450 MB, so its
@@ -567,6 +577,9 @@ What happens at each limit:
   and after the held-back messages of every peer whose session went down before
   it. It holds at most 150,000 such messages, about 150 MiB. At that number it
   takes nothing more off its queue until it has applied one of them.
+- Waiting origin changes: the routing table keeps at most 100,000 origin changes
+  waiting to be written. Past that, it drops the oldest, and the prefix handler
+  logs how many. The prefix page never shows a dropped origin change.
 
 To replace the image's Go soft limit, set `GOMEMLIMIT` in the environment, for
 example `-e GOMEMLIMIT=3GiB`. A limit close to the routing table's size makes
@@ -620,8 +633,9 @@ The parts:
   messages. It gives each message to the handlers that want it, through one
   queue per handler.
 - The prefix handler keeps the routing table in memory current. Every second it
-  writes the table's changes to the `routes` table of the database. It also
-  stores each new prefix with the time it was first seen.
+  writes the table's changes to the `routes` table and the table's origin
+  changes to the `origin_changes` table of the database. It also stores each new
+  prefix with the time it was first seen.
 - The AS handler records every AS seen in an AS path in the `asns` table, with
   the times it was first and last seen.
 - The peer handler records every peer in the `bgp_peers` table.
@@ -638,11 +652,14 @@ The parts:
 - The database maintainer checkpoints the database every 5 seconds: it folds the
   write-ahead log, where SQLite first writes changes, into the database file. It
   reclaims free space every 10 minutes. Every hour it refreshes the statistics
-  SQLite uses to plan its queries.
+  SQLite uses to plan its queries, and prunes the `origin_changes` table. A
+  prune keeps each prefix's rows from the last 72 hours, or its newest 500,
+  whichever keeps more.
 - The HTTP server serves the pages and the API. Every route it shows comes from
-  the routing table in memory. WHOIS details and first-seen times come from the
-  database. AS names come from the database or from the AS list built into
-  RouteWatch. The AS name search reads the AS list built into RouteWatch.
+  the routing table in memory. WHOIS details, first-seen times and origin
+  changes come from the database. AS names come from the database or from the AS
+  list built into RouteWatch. The AS name search reads the AS list built into
+  RouteWatch.
 
 ### The routing table
 
@@ -753,6 +770,8 @@ What a stop can lose:
   changed pairs. A full-table peer is a peer that carries the whole routing
   table. Its session going down changes about a million pairs, which take about
   a minute to write. A stop in that minute leaves the rest unwritten.
+- The prefix handler's last write of origin changes takes at most 20,000. The
+  rest are lost.
 - A withdrawal, or a session going down, that is lost this way leaves its routes
   in the `routes` table. The next start reads them back. They stay until the
   peer sends another update for the prefix, or its session goes down again.
@@ -809,6 +828,10 @@ routes(prefix, origin_asn, peers,
 -- The peers of the routes table, each with its number in the peer sets
 route_peers(number PRIMARY KEY, address UNIQUE)
 
+-- The origin changes of the routing table: each time a prefix and origin AS
+-- gained its first peer or lost its last
+origin_changes(id PRIMARY KEY, prefix, origin_asn, announced, peer_count, time)
+
 peerings(id PRIMARY KEY, as_a, as_b, first_seen, last_seen,
          UNIQUE(as_a, as_b))
 bgp_peers(id PRIMARY KEY, peer_ip UNIQUE, peer_asn, first_seen, last_seen,

TODO.md

@@ -41,9 +41,8 @@ https://git.eeqj.de/sneak/routewatch/issues/225, also on `next`, takes the peers
 whose sessions go down together out of the table in one walk. A 24-hour run of
 `9bd0e91` on the live feed is checking whether any handler still drops updates.
 
-Two questions wait for sneak: which history the prefix page keeps
-(https://git.eeqj.de/sneak/routewatch/issues/161), and which fields the IP
-lookup answer gains (https://git.eeqj.de/sneak/routewatch/issues/203).
+One question waits for sneak: which fields the IP lookup answer gains
+(https://git.eeqj.de/sneak/routewatch/issues/203).
 
 The order of the project's remaining work is kept on
 https://git.eeqj.de/sneak/routewatch/issues/86.
@@ -57,6 +56,19 @@ problem the run finds.
 
 # Completed Steps
 
+- 2026-11-05: the prefix page lists the prefix's origin changes, newest first.
+  The routing table records each change, and the prefix handler writes them to a
+  new `origin_changes` table. The database maintainer prunes each prefix to its
+  newest 500 rows or its rows from the last 72 hours, whichever keeps more. The
+  page shows at most the newest 5,000. Each row shows:
+    - the time
+    - announced or withdrawn
+    - the origin AS
+    - the peer count
+
+    A row's peer count is how many peers carry the prefix just after the change,
+    with any origin AS (closes #161).
+
 - 2026-11-03: the streamer drops an update for a handler only when that
   handler's queue is full. It used to drop a random share of the updates once
   the queue was half full. The prefix handler's queue now holds 100,000

internal/database/interface.go

@@ -1,6 +1,7 @@
 // Package database provides SQLite storage for BGP routing data: ASNs,
-// prefixes, announcements, peerings and BGP peers. Its routes table holds a
-// copy of the whole routing table that internal/routetable keeps in memory.
+// prefixes, announcements, peerings, BGP peers and origin changes. Its routes
+// table holds a copy of the whole routing table that internal/routetable
+// keeps in memory.
 package database
 
 import (
@@ -55,6 +56,14 @@ type Store interface {
 	WriteRouteChanges(changes []routetable.Change, newPeers map[string]uint) error
 	ReadRouteTable(ctx context.Context) (*routetable.Table, error)
 
+	// Origin change operations: the prefix and origin AS pairs' first and
+	// last peers, as the routing table records them.
+	WriteOriginChanges(changes []routetable.OriginChange) error
+	GetOriginChanges(
+		ctx context.Context, prefix netip.Prefix, limit int,
+	) ([]routetable.OriginChange, error)
+	PruneOriginChanges(ctx context.Context) error
+
 	// ASN WHOIS operations
 	GetNextStaleASN(ctx context.Context, staleThreshold time.Duration) (int, error)
 	UpdateASNWHOIS(ctx context.Context, update *ASNWHOISUpdate) error

internal/database/originchanges.go

@@ -0,0 +1,172 @@
+package database
+
+import (
+	"context"
+	"fmt"
+	"net/netip"
+	"time"
+
+	"git.eeqj.de/sneak/routewatch/internal/routetable"
+)
+
+// minOriginChangesPerPrefix is how many of a prefix's newest origin changes
+// the prune always keeps, whatever their age.
+const minOriginChangesPerPrefix = 500
+
+// originChangesRetention is how long the prune keeps an origin change: rows
+// older than this are deleted, unless they are among the prefix's newest
+// minOriginChangesPerPrefix.
+const originChangesRetention = 72 * time.Hour
+
+// The statements of the origin_changes table (schema.sql).
+const (
+	insertOriginChangeSQL = `INSERT INTO origin_changes
+		(prefix, origin_asn, announced, peer_count, time)
+		VALUES (?, ?, ?, ?, ?)`
+	originChangesSQL = `SELECT prefix, origin_asn, announced, peer_count, time
+		FROM origin_changes WHERE prefix = ? ORDER BY id DESC LIMIT ?`
+	prunePrefixesSQL = `SELECT prefix FROM origin_changes
+		GROUP BY prefix HAVING COUNT(*) > ?`
+	pruneOriginChangesSQL = `DELETE FROM origin_changes
+		WHERE prefix = ? AND time < ? AND id < (
+			SELECT id FROM origin_changes WHERE prefix = ?
+			ORDER BY id DESC LIMIT 1 OFFSET ?)`
+)
+
+// WriteOriginChanges writes, in one transaction, the origin changes the
+// routing table handed over. When it fails, it writes nothing; the caller then
+// writes them again.
+func (d *Database) WriteOriginChanges(changes []routetable.OriginChange) error {
+	if len(changes) == 0 {
+		return nil
+	}
+
+	d.lock("WriteOriginChanges")
+	defer d.unlock()
+
+	tx, err := d.beginTx()
+	if err != nil {
+		return fmt.Errorf("failed to begin transaction: %w", err)
+	}
+	defer d.rollback(tx)
+
+	ctx := context.Background()
+
+	stmt, err := tx.PrepareContext(ctx, insertOriginChangeSQL)
+	if err != nil {
+		return fmt.Errorf("failed to prepare origin change insert: %w", err)
+	}
+	defer func() { _ = stmt.Close() }()
+
+	for _, change := range changes {
+		_, err := stmt.ExecContext(ctx, change.Prefix.String(),
+			change.OriginASN, change.Announced, change.PeerCount,
+			change.Time.Unix())
+		if err != nil {
+			return fmt.Errorf("failed to write origin change %s: %w",
+				change.Prefix, err)
+		}
+	}
+
+	err = tx.Commit()
+	if err != nil {
+		return fmt.Errorf("failed to commit transaction: %w", err)
+	}
+
+	return nil
+}
+
+// GetOriginChanges returns at most limit of prefix's origin changes, newest
+// first.
+func (d *Database) GetOriginChanges(
+	ctx context.Context, prefix netip.Prefix, limit int,
+) ([]routetable.OriginChange, error) {
+	rows, err := d.db.QueryContext(ctx, originChangesSQL,
+		prefix.Masked().String(), limit)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read origin changes: %w", err)
+	}
+	defer func() { _ = rows.Close() }()
+
+	var changes []routetable.OriginChange
+
+	for rows.Next() {
+		var (
+			change     routetable.OriginChange
+			prefixText string
+			timeSec    int64
+		)
+
+		err := rows.Scan(&prefixText, &change.OriginASN, &change.Announced,
+			&change.PeerCount, &timeSec)
+		if err != nil {
+			return nil, fmt.Errorf("failed to read an origin change: %w", err)
+		}
+
+		change.Prefix, err = netip.ParsePrefix(prefixText)
+		if err != nil {
+			return nil, fmt.Errorf("failed to read origin change %s: %w",
+				prefixText, err)
+		}
+
+		change.Time = time.Unix(timeSec, 0).UTC()
+		changes = append(changes, change)
+	}
+
+	err = rows.Err()
+	if err != nil {
+		return nil, fmt.Errorf("failed to read origin changes: %w", err)
+	}
+
+	return changes, nil
+}
+
+// PruneOriginChanges deletes, for each prefix with more than
+// minOriginChangesPerPrefix rows, the rows older than originChangesRetention
+// that are not among its newest minOriginChangesPerPrefix. It finds those
+// prefixes on a reading connection and deletes one prefix per write, so no
+// write holds the lock for long.
+func (d *Database) PruneOriginChanges(ctx context.Context) error {
+	rows, err := d.db.QueryContext(ctx, prunePrefixesSQL,
+		minOriginChangesPerPrefix)
+	if err != nil {
+		return fmt.Errorf("failed to find prefixes to prune: %w", err)
+	}
+	defer func() { _ = rows.Close() }()
+
+	var prefixes []string
+
+	for rows.Next() {
+		var prefix string
+
+		err := rows.Scan(&prefix)
+		if err != nil {
+			return fmt.Errorf("failed to read a prefix to prune: %w", err)
+		}
+
+		prefixes = append(prefixes, prefix)
+	}
+
+	err = rows.Err()
+	if err != nil {
+		return fmt.Errorf("failed to find prefixes to prune: %w", err)
+	}
+
+	cutoff := time.Now().Add(-originChangesRetention).Unix()
+
+	for _, prefix := range prefixes {
+		d.lock("PruneOriginChanges")
+
+		_, err := d.writer.ExecContext(ctx, pruneOriginChangesSQL,
+			prefix, cutoff, prefix, minOriginChangesPerPrefix-1)
+
+		d.unlock()
+
+		if err != nil {
+			return fmt.Errorf("failed to prune origin changes of %s: %w",
+				prefix, err)
+		}
+	}
+
+	return nil
+}

internal/database/originchanges_internal_test.go

@@ -0,0 +1,217 @@
+package database
+
+import (
+	"net/netip"
+	"reflect"
+	"testing"
+	"time"
+
+	"git.eeqj.de/sneak/routewatch/internal/routetable"
+)
+
+// TestOriginChangesWriteThenRead writes three origin changes and reads them
+// back newest first, honouring the limit.
+func TestOriginChangesWriteThenRead(t *testing.T) {
+	t.Parallel()
+
+	db := newRoutesTestDatabase(t)
+	prefix := netip.MustParsePrefix(tablePrefixV4)
+
+	changes := []routetable.OriginChange{
+		{Prefix: prefix, OriginASN: asA, Announced: true, PeerCount: 1,
+			Time: tableTime(10)},
+		{Prefix: prefix, OriginASN: asA, Announced: false, PeerCount: 0,
+			Time: tableTime(20)},
+		{Prefix: prefix, OriginASN: asB, Announced: true, PeerCount: 1,
+			Time: tableTime(30)},
+	}
+
+	err := db.WriteOriginChanges(changes)
+	if err != nil {
+		t.Fatalf("WriteOriginChanges: %v", err)
+	}
+
+	got, err := db.GetOriginChanges(t.Context(), prefix, 2)
+	if err != nil {
+		t.Fatalf("GetOriginChanges: %v", err)
+	}
+
+	want := []routetable.OriginChange{
+		{Prefix: prefix, OriginASN: asB, Announced: true, PeerCount: 1,
+			Time: tableTime(30)},
+		{Prefix: prefix, OriginASN: asA, Announced: false, PeerCount: 0,
+			Time: tableTime(20)},
+	}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("GetOriginChanges = %+v, want %+v", got, want)
+	}
+}
+
+// TestOriginChangesPrune checks that the prune keeps, for a prefix with more
+// than 500 rows, its newest 500 rows and every row newer than 72 hours, and
+// deletes the rest. It checks which rows survive by their times, not only how
+// many.
+func TestOriginChangesPrune(t *testing.T) {
+	t.Parallel()
+
+	db := newRoutesTestDatabase(t)
+	oldPrefix := netip.MustParsePrefix(tablePrefixV4)
+	straddling := netip.MustParsePrefix(tablePrefixShortV4)
+	busy := netip.MustParsePrefix(tablePrefixBusyV4)
+	other := netip.MustParsePrefix("10.20.0.0/16")
+
+	// Whole seconds, so the stored times round-trip exactly.
+	now := time.Now().Truncate(time.Second)
+
+	// 600 rows for oldPrefix, all older than 72 hours, oldest first. The
+	// prune keeps the newest 500 and deletes the oldest 100.
+	changes := rows(oldPrefix, now.Add(-100*time.Hour), 600)
+	// 600 rows for straddling: 400 older than 72 hours, then 200 newer. The
+	// prune keeps all 200 newer and the newest 300 of the 400 older.
+	changes = append(changes, rows(straddling, now.Add(-100*time.Hour), 400)...)
+	changes = append(changes, rows(straddling, now.Add(-71*time.Hour), 200)...)
+	// 100 rows older than 72 hours and minOriginChangesPerPrefix+100 newer
+	// rows for busy. The prune keeps all the newer rows and none of the older,
+	// because the newer rows alone are more than minOriginChangesPerPrefix.
+	changes = append(changes, rows(busy, now.Add(-100*time.Hour), 100)...)
+	changes = append(changes, rows(busy, now.Add(-71*time.Hour),
+		minOriginChangesPerPrefix+100)...)
+	// One row for other, which the prune leaves alone.
+	changes = append(changes, rows(other, now.Add(-100*time.Hour), 1)...)
+
+	err := db.WriteOriginChanges(changes)
+	if err != nil {
+		t.Fatalf("WriteOriginChanges: %v", err)
+	}
+
+	err = db.PruneOriginChanges(t.Context())
+	if err != nil {
+		t.Fatalf("PruneOriginChanges: %v", err)
+	}
+
+	// The newest row survives, and the oldest survivor is the 100th oldest,
+	// so a prune that kept the oldest 500 instead would fail.
+	checkSurvivors(t, db, oldPrefix, 500,
+		now.Add(-100*time.Hour).Add(599*time.Minute),
+		now.Add(-100*time.Hour).Add(100*time.Minute))
+
+	// The newest of the newer-than-72-hours rows survives, and the oldest
+	// survivor is the 100th oldest of the older-than-72-hours rows.
+	checkSurvivors(t, db, straddling, 500,
+		now.Add(-71*time.Hour).Add(199*time.Minute),
+		now.Add(-100*time.Hour).Add(100*time.Minute))
+
+	// Every newer-than-72-hours row survives, so the oldest survivor is the
+	// first of them and the newest is minOriginChangesPerPrefix+99 minutes
+	// after it.
+	checkSurvivors(t, db, busy, minOriginChangesPerPrefix+100,
+		now.Add(-71*time.Hour).
+			Add(time.Duration(minOriginChangesPerPrefix+99)*time.Minute),
+		now.Add(-71*time.Hour))
+
+	gotOther, err := db.GetOriginChanges(t.Context(), other, 10)
+	if err != nil {
+		t.Fatalf("GetOriginChanges: %v", err)
+	}
+
+	if len(gotOther) != 1 {
+		t.Errorf("GetOriginChanges(other) = %d rows, want 1", len(gotOther))
+	}
+}
+
+// rows returns n origin changes for prefix, at times from plus one minute per
+// step, oldest first.
+func rows(prefix netip.Prefix, from time.Time, n int) []routetable.OriginChange {
+	changes := make([]routetable.OriginChange, 0, n)
+
+	for i := range n {
+		changes = append(changes, routetable.OriginChange{
+			Prefix: prefix, OriginASN: asA, Announced: true, PeerCount: 1,
+			Time: from.Add(time.Duration(i) * time.Minute),
+		})
+	}
+
+	return changes
+}
+
+// survivorTimes returns the times of prefix's rows after the prune, newest
+// first.
+func survivorTimes(
+	t *testing.T, db *Database, prefix netip.Prefix, limit int,
+) []time.Time {
+	t.Helper()
+
+	rows, err := db.GetOriginChanges(t.Context(), prefix, limit)
+	if err != nil {
+		t.Fatalf("GetOriginChanges: %v", err)
+	}
+
+	times := make([]time.Time, len(rows))
+	for i, row := range rows {
+		times[i] = row.Time
+	}
+
+	return times
+}
+
+// checkSurvivors checks that prefix kept exactly wantCount rows, with the
+// newest survivor at wantNewest and the oldest at wantOldest.
+func checkSurvivors(
+	t *testing.T, db *Database, prefix netip.Prefix,
+	wantCount int, wantNewest, wantOldest time.Time,
+) {
+	t.Helper()
+
+	times := survivorTimes(t, db, prefix, wantCount+1)
+	if len(times) != wantCount {
+		t.Errorf("GetOriginChanges(%s) = %d rows, want %d",
+			prefix, len(times), wantCount)
+
+		return
+	}
+
+	if !times[0].Equal(wantNewest) {
+		t.Errorf("the newest surviving row's time = %v, want %v",
+			times[0], wantNewest)
+	}
+
+	if !times[wantCount-1].Equal(wantOldest) {
+		t.Errorf("the oldest surviving row's time = %v, want %v",
+			times[wantCount-1], wantOldest)
+	}
+}
+
+// TestOriginChangesSurviveRouteDeletion checks that deleting a routes row
+// leaves the prefix's origin_changes rows.
+func TestOriginChangesSurviveRouteDeletion(t *testing.T) {
+	t.Parallel()
+
+	db := newRoutesTestDatabase(t)
+	prefix := netip.MustParsePrefix(tablePrefixV4)
+
+	err := db.WriteOriginChanges([]routetable.OriginChange{{
+		Prefix: prefix, OriginASN: asA, Announced: true, PeerCount: 1,
+		Time: tableTime(10),
+	}})
+	if err != nil {
+		t.Fatalf("WriteOriginChanges: %v", err)
+	}
+
+	// Write a route, then delete it.
+	table := routetable.New(routetable.Params{})
+	announceTo(table, tablePrefixV4, asA, peerA, 10)
+	writeTableChanges(t, db, table)
+
+	table.Withdraw(prefix, peerA)
+	writeTableChanges(t, db, table)
+
+	got, err := db.GetOriginChanges(t.Context(), prefix, 10)
+	if err != nil {
+		t.Fatalf("GetOriginChanges: %v", err)
+	}
+
+	if len(got) != 1 {
+		t.Errorf("GetOriginChanges = %d rows, want 1", len(got))
+	}
+}

internal/database/routes_internal_test.go

@@ -34,6 +34,7 @@ const (
 
 	tablePrefixV4      = "10.1.2.0/24"
 	tablePrefixShortV4 = "10.9.0.0/16"
+	tablePrefixBusyV4  = "10.10.0.0/16"
 	tablePrefixV6      = "2001:db8:1::/48"
 )
 

internal/database/schema.sql

@@ -119,4 +119,20 @@ CREATE TABLE IF NOT EXISTS routes (
 CREATE TABLE IF NOT EXISTS route_peers (
 	number INTEGER PRIMARY KEY,
 	address TEXT NOT NULL UNIQUE
-);
+);
+
+-- The origin changes of the routing table: each time a prefix and origin AS
+-- gained its first peer or lost its last. The prefix handler writes them, and
+-- the database maintainer prunes each prefix to its newest 500 rows or its
+-- rows from the last 72 hours, whichever keeps more. time is whole seconds
+-- since 1970, UTC.
+CREATE TABLE IF NOT EXISTS origin_changes (
+	id INTEGER PRIMARY KEY,
+	prefix TEXT NOT NULL,
+	origin_asn INTEGER NOT NULL,
+	announced BOOLEAN NOT NULL,
+	peer_count INTEGER NOT NULL,
+	time INTEGER NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS idx_origin_changes_prefix ON origin_changes(prefix);

internal/routetable/originchanges.go

@@ -0,0 +1,103 @@
+package routetable
+
+import (
+	"net/netip"
+	"slices"
+	"time"
+)
+
+// MaxWaitingOriginChanges is the most origin changes the table keeps waiting
+// for the prefix handler to write. The oldest change past it is dropped and
+// counted.
+const MaxWaitingOriginChanges = 100000
+
+// OriginChange is one change of a prefix and origin AS pair: the origin AS
+// gained its first peer, or lost its last.
+type OriginChange struct {
+	Prefix    netip.Prefix
+	OriginASN int
+	// Announced says the origin AS gained its first peer. When false, it
+	// lost its last peer.
+	Announced bool
+	// PeerCount is how many peers carry the prefix just after the change,
+	// counting every origin AS.
+	PeerCount int
+	// Time is when RouteWatch applied the change.
+	Time time.Time
+}
+
+// recordOriginChange records that the pair of prefix and asn gained its first
+// peer, when announced, or lost its last, when not. The caller holds the lock.
+// peerCount is how many peers carry the prefix just after the change.
+func (t *Table) recordOriginChange(
+	prefix netip.Prefix, asn int, announced bool, peerCount int,
+) {
+	change := OriginChange{
+		Prefix:    prefix,
+		OriginASN: asn,
+		Announced: announced,
+		PeerCount: peerCount,
+		Time:      t.now(),
+	}
+
+	t.originChanges = append(t.originChanges, change)
+	t.trimOriginChanges()
+}
+
+// TakeOriginChanges returns at most limit of the origin changes that wait to
+// be written, oldest first, and how many were dropped since the last call. It
+// then forgets what it returned.
+func (t *Table) TakeOriginChanges(limit int) ([]OriginChange, int) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	n := min(limit, len(t.originChanges))
+	changes := slices.Clone(t.originChanges[:n])
+	t.originChanges = t.originChanges[n:]
+
+	dropped := t.originChangesDropped
+	t.originChangesDropped = 0
+
+	return changes, dropped
+}
+
+// PutBackOriginChanges records again what one TakeOriginChanges call returned,
+// for a caller that could not write it. The next TakeOriginChanges returns
+// those changes first, before the ones that arrived since. The oldest changes
+// past the cap are dropped and counted.
+func (t *Table) PutBackOriginChanges(changes []OriginChange) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	t.originChanges = append(changes, t.originChanges...)
+	t.trimOriginChanges()
+}
+
+// trimOriginChanges drops the oldest origin changes past the cap and counts
+// them. The caller holds the lock.
+func (t *Table) trimOriginChanges() {
+	if extra := len(t.originChanges) - MaxWaitingOriginChanges; extra > 0 {
+		t.originChangesDropped += extra
+		t.originChanges = t.originChanges[extra:]
+	}
+}
+
+// OriginChangeCount returns how many origin changes wait for TakeOriginChanges.
+func (t *Table) OriginChangeCount() int {
+	t.mu.RLock()
+	defer t.mu.RUnlock()
+
+	return len(t.originChanges)
+}
+
+// prefixPeerCount returns how many peers carry prefix, counting every origin
+// AS. The caller holds the lock.
+func (t *Table) prefixPeerCount(prefix netip.Prefix) int {
+	count := 0
+
+	for _, o := range t.origins(prefix) {
+		count += int(o.peers.Count())
+	}
+
+	return count
+}

internal/routetable/originchanges_test.go

@@ -0,0 +1,302 @@
+package routetable_test
+
+import (
+	"math"
+	"net/netip"
+	"reflect"
+	"testing"
+	"time"
+
+	"github.com/bits-and-blooms/bitset"
+
+	"git.eeqj.de/sneak/routewatch/internal/routetable"
+)
+
+// originChange returns the origin change the table records for prefix and asn
+// at the clock's time, announced or withdrawn, with peerCount peers.
+func originChange(
+	prefix netip.Prefix, asn int, announced bool, peerCount int, at time.Time,
+) routetable.OriginChange {
+	return routetable.OriginChange{
+		Prefix:    prefix,
+		OriginASN: asn,
+		Announced: announced,
+		PeerCount: peerCount,
+		Time:      at,
+	}
+}
+
+// TestOriginChangesRecordAnnouncedAndWithdrawn checks that a prefix and origin
+// AS pair records an announced row when it gains its first peer, nothing for a
+// second peer, and a withdrawn row when it loses its last peer.
+func TestOriginChangesRecordAnnouncedAndWithdrawn(t *testing.T) {
+	t.Parallel()
+
+	now := at(0)
+	table := routetable.New(routetable.Params{
+		Now: func() time.Time { return now },
+	})
+	prefix := netip.MustParsePrefix(prefixV4)
+
+	table.Announce(prefix, asA, routeOf(peerA, asA, 10))
+	table.Announce(prefix, asA, routeOf(peerB, asA, 20))
+
+	checkOriginChanges(t, table, []routetable.OriginChange{
+		originChange(prefix, asA, true, 1, now),
+	})
+
+	table.Withdraw(prefix, peerA)
+	table.Withdraw(prefix, peerB)
+
+	checkOriginChanges(t, table, []routetable.OriginChange{
+		originChange(prefix, asA, false, 0, now),
+	})
+}
+
+// TestOriginChangesRecordAPeerMovingOrigin checks that a peer moving from one
+// origin AS to another records a withdrawn row for the old one and an
+// announced row for the new one.
+func TestOriginChangesRecordAPeerMovingOrigin(t *testing.T) {
+	t.Parallel()
+
+	now := at(0)
+	table := routetable.New(routetable.Params{
+		Now: func() time.Time { return now },
+	})
+	prefix := netip.MustParsePrefix(prefixV4)
+
+	table.Announce(prefix, asA, routeOf(peerA, asA, 10))
+	table.Announce(prefix, asB, routeOf(peerA, asB, 20))
+
+	checkOriginChanges(t, table, []routetable.OriginChange{
+		originChange(prefix, asA, true, 1, now),
+		originChange(prefix, asA, false, 0, now),
+		originChange(prefix, asB, true, 1, now),
+	})
+}
+
+// TestOriginChangesRecordPeersDown checks that PeersDown records a withdrawn
+// row for each prefix and origin AS pair it empties.
+func TestOriginChangesRecordPeersDown(t *testing.T) {
+	t.Parallel()
+
+	now := at(0)
+	table := routetable.New(routetable.Params{
+		Now: func() time.Time { return now },
+	})
+	v4 := netip.MustParsePrefix(prefixV4)
+	v6 := netip.MustParsePrefix(prefixV6)
+
+	table.Announce(v4, asA, routeOf(peerA, asA, 10))
+	table.Announce(v6, asA, routeOf(peerA, asA, 10))
+	table.Announce(v4, asB, routeOf(peerB, asB, 20))
+
+	table.PeersDown([]string{peerA})
+
+	// peerA carried v4 and v6 with asA; both pairs are emptied. peerB still
+	// carries v4 with asB, so that pair is not.
+	checkOriginChanges(t, table, []routetable.OriginChange{
+		originChange(v4, asA, true, 1, now),
+		originChange(v6, asA, true, 1, now),
+		originChange(v4, asB, true, 2, now),
+		originChange(v4, asA, false, 1, now),
+		originChange(v6, asA, false, 0, now),
+	})
+}
+
+// TestOriginChangesLoadRecordsNothing checks that Load records no origin
+// change.
+func TestOriginChangesLoadRecordsNothing(t *testing.T) {
+	t.Parallel()
+
+	table := routetable.New(routetable.Params{
+		PeerNumbers: map[string]uint{peerA: 0},
+	})
+	prefix := netip.MustParsePrefix(prefixV4)
+
+	peers := new(bitset.BitSet)
+	peers.Set(0)
+
+	table.Load(routetable.Change{
+		Prefix:    prefix,
+		OriginASN: asA,
+		Peers:     peers,
+		Routes:    []routetable.Route{routeOf(peerA, asA, 10)},
+	})
+
+	changes, dropped := table.TakeOriginChanges(math.MaxInt)
+	if dropped != 0 || len(changes) != 0 {
+		t.Errorf("TakeOriginChanges = %+v, %d; want none", changes, dropped)
+	}
+}
+
+// TestOriginChangesTakeReturnsOldestFirst checks that TakeOriginChanges
+// returns the changes oldest first and at most max.
+func TestOriginChangesTakeReturnsOldestFirst(t *testing.T) {
+	t.Parallel()
+
+	table := routetable.New(routetable.Params{})
+	prefix := netip.MustParsePrefix(prefixV4)
+
+	table.Announce(prefix, asA, routeOf(peerA, asA, 10))
+	table.Announce(prefix, asB, routeOf(peerB, asB, 20))
+	table.Announce(prefix, asC, routeOf(peerC, asC, 30))
+
+	first, dropped := table.TakeOriginChanges(2)
+	if dropped != 0 {
+		t.Errorf("dropped = %d, want 0", dropped)
+	}
+
+	if len(first) != 2 || first[0].OriginASN != asA || first[1].OriginASN != asB {
+		t.Errorf("first TakeOriginChanges = %+v, want the first two", first)
+	}
+
+	second, _ := table.TakeOriginChanges(math.MaxInt)
+	if len(second) != 1 || second[0].OriginASN != asC {
+		t.Errorf("second TakeOriginChanges = %+v, want the third", second)
+	}
+}
+
+// TestOriginChangesPutBackPutsRowsInFront checks that PutBackOriginChanges
+// puts rows back in front, so the next TakeOriginChanges returns them first.
+func TestOriginChangesPutBackPutsRowsInFront(t *testing.T) {
+	t.Parallel()
+
+	table := routetable.New(routetable.Params{})
+	prefix := netip.MustParsePrefix(prefixV4)
+
+	table.Announce(prefix, asA, routeOf(peerA, asA, 10))
+	table.Announce(prefix, asB, routeOf(peerB, asB, 20))
+
+	taken, _ := table.TakeOriginChanges(math.MaxInt)
+	table.Announce(prefix, asC, routeOf(peerC, asC, 30))
+	table.PutBackOriginChanges(taken)
+
+	changes, _ := table.TakeOriginChanges(math.MaxInt)
+	if len(changes) != 3 || changes[0].OriginASN != asA ||
+		changes[1].OriginASN != asB || changes[2].OriginASN != asC {
+		t.Errorf("TakeOriginChanges = %+v, want the put-back rows first", changes)
+	}
+}
+
+// TestOriginChangesDropPastTheLimit checks that a change past 100,000 waiting
+// rows is dropped and counted.
+func TestOriginChangesDropPastTheLimit(t *testing.T) {
+	t.Parallel()
+
+	table := routetable.New(routetable.Params{})
+	addr := netip.MustParseAddr("10.0.0.0")
+
+	for range routetable.MaxWaitingOriginChanges + 1 {
+		prefix := netip.PrefixFrom(addr, 32)
+		table.Announce(prefix, asA, routeOf(peerA, asA, 10))
+
+		addr = addr.Next()
+	}
+
+	changes, dropped := table.TakeOriginChanges(routetable.MaxWaitingOriginChanges)
+	if dropped != 1 {
+		t.Errorf("dropped = %d, want 1", dropped)
+	}
+
+	if len(changes) != routetable.MaxWaitingOriginChanges {
+		t.Errorf("len(changes) = %d, want %d", len(changes),
+			routetable.MaxWaitingOriginChanges)
+	}
+}
+
+// TestOriginChangesTakeResetsTheDroppedCount checks that a TakeOriginChanges
+// that reports dropped rows leaves the next one reporting none, so each drop
+// is logged once, not on every later write.
+func TestOriginChangesTakeResetsTheDroppedCount(t *testing.T) {
+	t.Parallel()
+
+	table := routetable.New(routetable.Params{})
+	addr := netip.MustParseAddr("10.0.0.0")
+
+	for range routetable.MaxWaitingOriginChanges + 1 {
+		table.Announce(netip.PrefixFrom(addr, 32), asA, routeOf(peerA, asA, 10))
+		addr = addr.Next()
+	}
+
+	_, dropped := table.TakeOriginChanges(routetable.MaxWaitingOriginChanges)
+	if dropped != 1 {
+		t.Fatalf("dropped = %d, want 1", dropped)
+	}
+
+	_, dropped = table.TakeOriginChanges(0)
+	if dropped != 0 {
+		t.Errorf("the next take's dropped = %d, want 0", dropped)
+	}
+}
+
+// TestOriginChangesPutBackTrimsToTheLimit checks that putting back what a
+// failed write took, after new changes filled the table again, drops the
+// oldest changes past the cap and counts them, so the cap still holds. The
+// clock advances one second per change, so a change's time says its age.
+func TestOriginChangesPutBackTrimsToTheLimit(t *testing.T) {
+	t.Parallel()
+
+	const (
+		taken = 20000
+		added = 20000
+	)
+
+	now := time.Unix(0, 0)
+	table := routetable.New(routetable.Params{
+		Now: func() time.Time {
+			now = now.Add(time.Second)
+
+			return now
+		},
+	})
+	addr := netip.MustParseAddr("10.0.0.0")
+
+	announce := func(n int) {
+		for range n {
+			table.Announce(netip.PrefixFrom(addr, 32), asA, routeOf(peerA, asA, 10))
+			addr = addr.Next()
+		}
+	}
+
+	announce(routetable.MaxWaitingOriginChanges)
+
+	takenChanges, _ := table.TakeOriginChanges(taken)
+
+	announce(added)
+
+	table.PutBackOriginChanges(takenChanges)
+
+	changes, dropped := table.TakeOriginChanges(math.MaxInt)
+	if dropped != added {
+		t.Errorf("dropped = %d, want %d", dropped, added)
+	}
+
+	if len(changes) != routetable.MaxWaitingOriginChanges {
+		t.Errorf("len(changes) = %d, want %d", len(changes),
+			routetable.MaxWaitingOriginChanges)
+	}
+
+	// The put-back rows are the oldest, so they are the ones dropped. The
+	// first remaining change is the one that followed them.
+	if want := time.Unix(int64(added+1), 0); !changes[0].Time.Equal(want) {
+		t.Errorf("first change's time = %v, want %v", changes[0].Time, want)
+	}
+}
+
+// checkOriginChanges checks that TakeOriginChanges, taking every change,
+// returns want.
+func checkOriginChanges(
+	t *testing.T, table *routetable.Table, want []routetable.OriginChange,
+) {
+	t.Helper()
+
+	changes, dropped := table.TakeOriginChanges(math.MaxInt)
+	if dropped != 0 {
+		t.Errorf("dropped = %d, want 0", dropped)
+	}
+
+	if !reflect.DeepEqual(changes, want) {
+		t.Errorf("TakeOriginChanges = %+v, want %+v", changes, want)
+	}
+}

internal/routetable/routetable.go

@@ -2,7 +2,9 @@
 // and origin AS, it keeps the peers whose current route to the prefix has that
 // origin AS. It also keeps the two newest of those routes in full. It applies
 // announcements, withdrawals and peers' sessions going down. It answers the
-// route reads that the pages and the API need.
+// route reads that the pages and the API need. It also records each prefix and
+// origin AS pair's origin changes: when it gains its first peer and when it
+// loses its last.
 package routetable
 
 import (
@@ -91,6 +93,9 @@ type Params struct {
 	// peer not in it gets the next number above all of them the first time it
 	// announces a route.
 	PeerNumbers map[string]uint
+	// Now returns the time RouteWatch applies a change at. It is time.Now
+	// unless a test gives one.
+	Now func() time.Time
 }
 
 // Table is the routing table. Its methods are safe for concurrent use.
@@ -126,11 +131,24 @@ type Table struct {
 	// originsWithoutKeptRoute counts the origins that peers carry but that
 	// keep no route.
 	originsWithoutKeptRoute int
+
+	// now returns the time RouteWatch applies a change at.
+	now func() time.Time
+	// originChanges holds the origin changes that wait to be written, oldest
+	// first. originChangesDropped counts those dropped since the last
+	// TakeOriginChanges.
+	originChanges        []OriginChange
+	originChangesDropped int
 }
 
 // New returns an empty table that numbers new peers on from
 // params.PeerNumbers.
 func New(params Params) *Table {
+	now := params.Now
+	if now == nil {
+		now = time.Now
+	}
+
 	t := &Table{
 		ipv4:          newFamily(ipv4Bits, minLookupMaskLengthV4),
 		ipv6:          newFamily(ipv6Bits, minLookupMaskLengthV6),
@@ -139,6 +157,7 @@ func New(params Params) *Table {
 		peerAddresses: make(map[uint]string, len(params.PeerNumbers)),
 		newPeers:      make(map[string]uint),
 		changed:       make(map[pair]struct{}),
+		now:           now,
 		keptTimes: btree.NewG(keptTimesDegree, func(a, b keptTime) bool {
 			return a.time.Before(b.time)
 		}),
@@ -268,8 +287,9 @@ func (t *Table) PeersDown(peers []string) {
 // Load puts one prefix and origin AS pair that the database holds into the
 // table, as startup does with each row it reads. The change's peers join the
 // pair's peer set, and its routes are kept as an announcement's would be.
-// Unlike an update, Load records no change, so TakeChanges does not hand the
-// pair back to be written again. Loading a pair twice changes nothing.
+// Unlike an update, Load records no change and no origin change, so
+// TakeChanges does not hand the pair back to be written again. Loading a pair
+// twice changes nothing.
 //
 // The caller makes sure that every peer change names, in its peer set or in
 // its routes, has a number in Params.PeerNumbers.
@@ -460,6 +480,7 @@ func (t *Table) removeOrigin(prefix netip.Prefix, o *origin) {
 // r in full when it is one of the two newest routes of o. The peer's earlier
 // route, if o keeps one, is replaced: it is no longer the peer's current route.
 // The pair is recorded as changed only when its peer set or kept routes change.
+// When r is the origin's first peer, an announced origin change is recorded.
 func (t *Table) join(prefix netip.Prefix, o *origin, r route) {
 	if slices.ContainsFunc(o.routes, r.equal) {
 		// The peer announced its kept route again.
@@ -469,6 +490,8 @@ func (t *Table) join(prefix netip.Prefix, o *origin, r route) {
 	wasWithoutKeptRoute := o.withoutKeptRoute()
 
 	joined := !o.peers.Test(r.peer)
+
+	firstPeer := joined && o.peers.None()
 	if joined {
 		o.peers.Set(r.peer)
 
@@ -482,6 +505,10 @@ func (t *Table) join(prefix netip.Prefix, o *origin, r route) {
 	if joined || dropped || kept {
 		t.recordChange(prefix, o, wasWithoutKeptRoute)
 	}
+
+	if firstPeer {
+		t.recordOriginChange(prefix, o.asn, true, t.prefixPeerCount(prefix))
+	}
 }
 
 // leave takes peer out of the peer set of o, an origin of prefix, and drops
@@ -540,7 +567,8 @@ func (t *Table) dropKeptRoute(o *origin, peer uint) bool {
 // recordChange records that the pair of prefix and the AS of o changed, and
 // brings the count of origins without a kept route up to date.
 // wasWithoutKeptRoute says whether o was such an origin before the change. An
-// origin that no peer carries any more is removed.
+// origin that no peer carries any more is removed, and a withdrawn origin
+// change is recorded.
 func (t *Table) recordChange(
 	prefix netip.Prefix, o *origin, wasWithoutKeptRoute bool,
 ) {
@@ -549,6 +577,7 @@ func (t *Table) recordChange(
 	t.countOriginWithoutKeptRoute(o, wasWithoutKeptRoute)
 
 	if o.peers.None() {
+		t.recordOriginChange(prefix, o.asn, false, t.prefixPeerCount(prefix))
 		t.removeOrigin(prefix, o)
 	}
 }

internal/routewatch/app_integration_internal_test.go

@@ -330,6 +330,23 @@ func (m *mockStore) ReadRouteTable(_ context.Context) (*routetable.Table, error)
 	return routetable.New(routetable.Params{}), nil
 }
 
+// WriteOriginChanges records nothing: the mock keeps no origin changes.
+func (m *mockStore) WriteOriginChanges(_ []routetable.OriginChange) error {
+	return nil
+}
+
+// GetOriginChanges returns no origin changes.
+func (m *mockStore) GetOriginChanges(
+	_ context.Context, _ netip.Prefix, _ int,
+) ([]routetable.OriginChange, error) {
+	return nil, nil
+}
+
+// PruneOriginChanges does nothing.
+func (m *mockStore) PruneOriginChanges(_ context.Context) error {
+	return nil
+}
+
 // GetOrCreateASNBatch mock implementation
 func (m *mockStore) GetOrCreateASNBatch(asns map[int]database.SeenTimes) error {
 	m.mu.Lock()

internal/routewatch/batchwrite_internal_test.go

@@ -175,12 +175,13 @@ func (s *blockingStore) releaseWrites() {
 //
 //nolint:tagliatelle // field names are the keys the handlers log
 type stopLog struct {
-	Msg          string `json:"msg"`
-	Updates      int    `json:"updates"`
-	TableChanges int    `json:"table_changes"`
-	HeldMessages int    `json:"held_messages"`
-	Paths        int    `json:"paths"`
-	BatchEntries int    `json:"batch_entries"`
+	Msg           string `json:"msg"`
+	Updates       int    `json:"updates"`
+	TableChanges  int    `json:"table_changes"`
+	HeldMessages  int    `json:"held_messages"`
+	OriginChanges int    `json:"origin_changes"`
+	Paths         int    `json:"paths"`
+	BatchEntries  int    `json:"batch_entries"`
 }
 
 // newErrorLogger returns a logger that writes only errors, as JSON lines, to
@@ -472,6 +473,42 @@ func (s tableWriteBlockingStore) WriteRouteChanges(
 	return s.mockStore.WriteRouteChanges(changes, newPeers)
 }
 
+// stopPrefixHandlerWithBlockedWrite stops the prefix handler, whose store
+// holds the write that fill starts, after handing it the message extra, and
+// returns what Stop logged. blocking is the store the write waits on; store is
+// a blockingStore wrapped for the routing table's changes or the origin
+// changes.
+func stopPrefixHandlerWithBlockedWrite(
+	t *testing.T,
+	blocking *blockingStore,
+	store database.Store,
+	logs *bytes.Buffer,
+	fill, extra *ristypes.RISMessage,
+) stopLog {
+	t.Helper()
+
+	h := NewPrefixHandler(store, newErrorLogger(logs),
+		routetable.New(routetable.Params{}))
+	stopWhileAWriteIsBlocked(t, blocking, h, h.done,
+		[]*ristypes.RISMessage{fill}, extra)
+
+	return lastLogged(t, logs)
+}
+
+// originChangesBlockingStore is a blockingStore whose writes of the origin
+// changes also wait until the test calls releaseWrites.
+type originChangesBlockingStore struct {
+	*blockingStore
+}
+
+func (s originChangesBlockingStore) WriteOriginChanges(
+	changes []routetable.OriginChange,
+) error {
+	s.waitForRelease()
+
+	return s.mockStore.WriteOriginChanges(changes)
+}
+
 // TestPrefixHandlerStopCountsTheTableChangesOfAWriteInProgress holds the write
 // of the routing table's changes that a full batch starts, then hands the
 // prefix handler one more prefix and stops it with a deadline that passes
@@ -485,19 +522,67 @@ func TestPrefixHandlerStopCountsTheTableChangesOfAWriteInProgress(t *testing.T)
 	var logs bytes.Buffer
 
 	blocking := newBlockingStore()
-	h := NewPrefixHandler(tableWriteBlockingStore{blockingStore: blocking},
-		newErrorLogger(&logs), routetable.New(routetable.Params{}))
 	fill := slices.Repeat([]string{testV4Prefix}, prefixBatchSize)
-	stopWhileAWriteIsBlocked(t, blocking, h, h.done,
-		[]*ristypes.RISMessage{prefixAnnouncement(fill)},
-		prefixAnnouncement([]string{extraPrefix}))
+	logged := stopPrefixHandlerWithBlockedWrite(t, blocking,
+		tableWriteBlockingStore{blockingStore: blocking}, &logs,
+		prefixAnnouncement(fill), prefixAnnouncement([]string{extraPrefix}))
 
-	if logged := lastLogged(t, &logs); logged.TableChanges != 2 {
+	if logged.TableChanges != 2 {
 		t.Errorf("Stop logged %d table changes not written, want 2",
 			logged.TableChanges)
 	}
 }
 
+// TestPrefixHandlerStopCountsTheOriginChangesOfAWriteInProgress holds the
+// write of the origin changes that a full batch starts, then hands the prefix
+// handler one more prefix and stops it with a deadline that passes meanwhile.
+// Stop must log as not written both the change the held write took and the one
+// since.
+func TestPrefixHandlerStopCountsTheOriginChangesOfAWriteInProgress(t *testing.T) {
+	t.Parallel()
+
+	const extraPrefix = "198.51.100.0/24"
+
+	var logs bytes.Buffer
+
+	blocking := newBlockingStore()
+	fill := slices.Repeat([]string{testV4Prefix}, prefixBatchSize)
+	logged := stopPrefixHandlerWithBlockedWrite(t, blocking,
+		originChangesBlockingStore{blockingStore: blocking}, &logs,
+		prefixAnnouncement(fill), prefixAnnouncement([]string{extraPrefix}))
+
+	if logged.OriginChanges != 2 {
+		t.Errorf("Stop logged %d origin changes not written, want 2",
+			logged.OriginChanges)
+	}
+}
+
+// TestPrefixHandlerStopCountsTheWaitingOriginChanges stops the prefix handler
+// with a deadline that has already passed, so the flush goroutine skips its
+// last write. The origin changes still waiting in the routing table are then
+// not written, and Stop must log them.
+func TestPrefixHandlerStopCountsTheWaitingOriginChanges(t *testing.T) {
+	t.Parallel()
+
+	var logs bytes.Buffer
+
+	store := newMockStore()
+	h := newPrefixHandler(store, newErrorLogger(&logs),
+		routetable.New(routetable.Params{}), longerThanAnyTest,
+		maxTableChangesPerWrite)
+
+	h.HandleMessage(peerAnnouncement(testPeerIP, testV4Prefix, testV6Prefix))
+
+	ctx, cancel := context.WithCancel(t.Context())
+	cancel()
+	h.Stop(ctx)
+
+	if logged := lastLogged(t, &logs); logged.OriginChanges != 2 {
+		t.Errorf("Stop logged %d origin changes not written, want 2",
+			logged.OriginChanges)
+	}
+}
+
 // TestASHandlerSkipsItsLastWriteAfterTheStopDeadline also checks what Stop
 // logs: the asnBatchSize entries of the held write and the entry for testASNB,
 // handled since, are not written.

internal/routewatch/dbmaintainer.go

@@ -25,6 +25,10 @@ const (
 	// analyzeInterval is how often to run ANALYZE.
 	analyzeInterval = 1 * time.Hour
 
+	// originChangesPruneInterval is how often to prune the origin_changes
+	// table.
+	originChangesPruneInterval = 1 * time.Hour
+
 	// checkpointTimeout is the max time for WAL checkpoint.
 	checkpointTimeout = 10 * time.Second
 
@@ -33,6 +37,9 @@ const (
 
 	// analyzeTimeout is the max time for ANALYZE.
 	analyzeTimeout = 5 * time.Minute
+
+	// originChangesPruneTimeout is the max time for the origin changes prune.
+	originChangesPruneTimeout = 5 * time.Minute
 )
 
 // checkpointIncompleteMessage is logged, at debug level like a completed
@@ -80,6 +87,7 @@ func (m *DBMaintainer) Start(ctx context.Context) {
 		"checkpoint_interval", checkpointInterval,
 		"vacuum_interval", vacuumInterval,
 		"analyze_interval", analyzeInterval,
+		"origin_changes_prune_interval", originChangesPruneInterval,
 	)
 }
 
@@ -111,6 +119,9 @@ func (m *DBMaintainer) run(ctx context.Context) {
 	analyzeTimer := time.NewTimer(analyzeInterval)
 	defer analyzeTimer.Stop()
 
+	pruneTimer := time.NewTimer(originChangesPruneInterval)
+	defer pruneTimer.Stop()
+
 	for {
 		select {
 		case <-m.stopCh:
@@ -127,6 +138,10 @@ func (m *DBMaintainer) run(ctx context.Context) {
 		case <-analyzeTimer.C:
 			m.runAnalyze(ctx)
 			analyzeTimer.Reset(analyzeInterval)
+
+		case <-pruneTimer.C:
+			m.runPruneOriginChanges(ctx)
+			pruneTimer.Reset(originChangesPruneInterval)
 		}
 	}
 }
@@ -175,6 +190,18 @@ func (m *DBMaintainer) runAnalyze(ctx context.Context) {
 	}
 }
 
+// runPruneOriginChanges prunes the origin_changes table.
+func (m *DBMaintainer) runPruneOriginChanges(ctx context.Context) {
+	duration, err := runWithTimeout(ctx, originChangesPruneTimeout,
+		m.db.PruneOriginChanges)
+	if err != nil {
+		m.logger.Error("Origin changes prune failed", "error", err,
+			"duration", duration)
+	} else {
+		m.logger.Debug("Origin changes pruned", "duration", duration)
+	}
+}
+
 // runWithTimeout runs operation with a context that ends after timeout and
 // returns how long it took and its error.
 func runWithTimeout(

internal/routewatch/prefixhandler.go

@@ -48,6 +48,10 @@ const (
 	// going down changes are written in about a minute.
 	maxTableChangesPerWrite = 20000
 
+	// maxOriginChangesPerWrite is the most origin changes of the routing
+	// table that one flush writes; the rest wait for the next flushes.
+	maxOriginChangesPerWrite = 20000
+
 	// maxHeldBackMessages is the most messages the handler holds back from
 	// peers whose session went down. A peer's messages are held back from
 	// the moment its session goes down until peerDown has applied them. If
@@ -81,8 +85,8 @@ const (
 // a time, and takes new messages in between. It holds back at most
 // maxHeldBackMessages messages.
 //
-// Each flush writes the table's changes to the database. It also stores each
-// prefix the updates name with the time it was first seen.
+// Each flush writes the table's changes and origin changes to the database.
+// It also stores each prefix the updates name with the time it was first seen.
 type PrefixHandler struct {
 	db      database.Store
 	logger  *logger.Logger
@@ -95,11 +99,14 @@ type PrefixHandler struct {
 	// tableChangesPerWrite is maxTableChangesPerWrite, except in tests that
 	// give a smaller one.
 	tableChangesPerWrite int
+	// originChangesPerWrite is maxOriginChangesPerWrite, except in tests that
+	// give a smaller one.
+	originChangesPerWrite int
 
-	// Batching. mu guards batch, writing and writingTableChanges: the
-	// flush goroutine takes them under mu and writes them after releasing
-	// mu, so HandleMessage waits for a database write only while batch is at
-	// batchMaxSize.
+	// Batching. mu guards batch, writing, writingTableChanges and
+	// writingOriginChanges: the flush goroutine takes them under mu and
+	// writes them after releasing mu, so HandleMessage waits for a database
+	// write only while batch is at batchMaxSize.
 	mu    sync.Mutex
 	batch []seenPrefix
 	// writing is how many updates the flush goroutine took and has not
@@ -108,6 +115,9 @@ type PrefixHandler struct {
 	// writingTableChanges is how many changes the flush goroutine took from
 	// the routing table and has not finished writing.
 	writingTableChanges int
+	// writingOriginChanges is how many origin changes the flush goroutine
+	// took from the routing table and has not finished writing.
+	writingOriginChanges int
 	// batchTaken is signalled when the flush goroutine takes batch; its L is
 	// &mu.
 	batchTaken  sync.Cond
@@ -190,17 +200,18 @@ func newPrefixHandler(
 	batchTimeout time.Duration, tableChangesPerWrite int,
 ) *PrefixHandler {
 	h := &PrefixHandler{
-		db:                   db,
-		logger:               logger,
-		table:                table,
-		batch:                make([]seenPrefix, 0, prefixBatchSize),
-		batchMaxSize:         prefixBatchMaxSize,
-		tableChangesPerWrite: tableChangesPerWrite,
-		batchFullCh:          make(chan struct{}, 1),
-		stopCh:               make(chan context.Context, 1),
-		done:                 make(chan struct{}),
-		heldBack:             make(map[string][]*ristypes.RISMessage),
-		tablePeersDown:       table.PeersDown,
+		db:                    db,
+		logger:                logger,
+		table:                 table,
+		batch:                 make([]seenPrefix, 0, prefixBatchSize),
+		batchMaxSize:          prefixBatchMaxSize,
+		tableChangesPerWrite:  tableChangesPerWrite,
+		originChangesPerWrite: maxOriginChangesPerWrite,
+		batchFullCh:           make(chan struct{}, 1),
+		stopCh:                make(chan context.Context, 1),
+		done:                  make(chan struct{}),
+		heldBack:              make(map[string][]*ristypes.RISMessage),
+		tablePeersDown:        table.PeersDown,
 	}
 	h.batchTaken.L = &h.mu
 	h.heldTaken.L = &h.mu
@@ -268,13 +279,13 @@ func (h *PrefixHandler) HeldBackCount() int {
 // back meanwhile to be applied. It gives up this wait once ctx ends. Then Stop
 // stops the flush goroutine and waits for it until ctx ends. The flush
 // goroutine makes one last flush before it returns. That flush writes at most
-// tableChangesPerWrite of the routing table's changes, and the prefixes of the
-// updates the handler holds. Once ctx has ended the flush goroutine skips that
-// last flush, and a write still running is lost when the process exits. A
-// failed write of the table's changes is not retried either. Stop logs how
-// many updates and table changes are not written. It also logs how many
-// held-back messages are not applied. The caller calls Stop once its last
-// HandleMessage has returned.
+// tableChangesPerWrite of the routing table's changes, originChangesPerWrite of
+// its origin changes, and the prefixes of the updates the handler holds. Once
+// ctx has ended the flush goroutine skips that last flush, and a write still
+// running is lost when the process exits. A failed write of the table's
+// changes is not retried either. Stop logs how many updates, table changes and
+// origin changes are not written. It also logs how many held-back messages are
+// not applied. The caller calls Stop once its last HandleMessage has returned.
 func (h *PrefixHandler) Stop(ctx context.Context) {
 	peerDownsDone := make(chan struct{})
 
@@ -299,23 +310,25 @@ func (h *PrefixHandler) Stop(ctx context.Context) {
 	unwritten := h.writing + len(h.batch)
 	tableChanges := h.writingTableChanges + h.table.ChangeCount()
 	heldMessages := h.heldCount
+	originChanges := h.writingOriginChanges + h.table.OriginChangeCount()
 	h.mu.Unlock()
 
-	if unwritten == 0 && tableChanges == 0 && heldMessages == 0 {
+	if unwritten == 0 && tableChanges == 0 && heldMessages == 0 &&
+		originChanges == 0 {
 		return
 	}
 
 	if ctx.Err() != nil {
 		h.logger.Error("Stop deadline passed before the prefix handler wrote "+
 			"its updates", "updates", unwritten, "table_changes", tableChanges,
-			"held_messages", heldMessages)
+			"held_messages", heldMessages, "origin_changes", originChanges)
 
 		return
 	}
 
 	h.logger.Error("The prefix handler stopped before it wrote everything",
 		"updates", unwritten, "table_changes", tableChanges,
-		"held_messages", heldMessages)
+		"held_messages", heldMessages, "origin_changes", originChanges)
 }
 
 // applyMessage applies msg. The caller holds mu. A peer's session going down
@@ -502,11 +515,12 @@ func (h *PrefixHandler) takeBatch() []seenPrefix {
 	return batch
 }
 
-// flushBatch writes the routing table's changes, then takes the pending batch
-// and stores the prefixes it names, without holding the mutex during the
-// writes.
+// flushBatch writes the routing table's changes and origin changes, then
+// takes the pending batch and stores the prefixes it names, without holding
+// the mutex during the writes.
 func (h *PrefixHandler) flushBatch() {
 	h.writeTableChanges()
+	h.writeOriginChanges()
 
 	batch := h.takeBatch()
 	if len(batch) == 0 {
@@ -608,6 +622,39 @@ func (h *PrefixHandler) writeTableChanges() {
 	}
 }
 
+// writeOriginChanges writes at most originChangesPerWrite of the routing
+// table's origin changes. When the write fails, they go back to the table, so
+// that a later write writes them again. A dropped change is logged as a
+// warning.
+func (h *PrefixHandler) writeOriginChanges() {
+	h.mu.Lock()
+	changes, dropped := h.table.TakeOriginChanges(h.originChangesPerWrite)
+	h.writingOriginChanges = len(changes)
+	h.mu.Unlock()
+
+	if dropped > 0 {
+		h.logger.Warn("Origin changes dropped", "dropped", dropped)
+	}
+
+	if len(changes) == 0 {
+		return
+	}
+
+	err := h.db.WriteOriginChanges(changes)
+
+	h.mu.Lock()
+	defer h.mu.Unlock()
+
+	h.writingOriginChanges = 0
+
+	if err != nil {
+		h.logger.Error("Failed to write the origin changes; the next flush "+
+			"retries", "changes", len(changes), "error", err)
+
+		h.table.PutBackOriginChanges(changes)
+	}
+}
+
 // canonicalPrefix returns prefix in the text form net/netip prints, the form
 // the prefix tables store and the IP lookup reads them in. The feed sends IPv6
 // announcements compressed ("2001:db8::/32") but IPv6 withdrawals uncompressed

internal/routewatch/prefixhandler_internal_test.go

@@ -327,13 +327,14 @@ func prefixHandlerWithoutTimer(store database.Store) *PrefixHandler {
 	table := routetable.New(routetable.Params{})
 
 	return &PrefixHandler{
-		db:                   store,
-		logger:               logger.New(),
-		table:                table,
-		batchMaxSize:         prefixBatchMaxSize,
-		tableChangesPerWrite: maxTableChangesPerWrite,
-		heldBack:             make(map[string][]*ristypes.RISMessage),
-		tablePeersDown:       table.PeersDown,
+		db:                    store,
+		logger:                logger.New(),
+		table:                 table,
+		batchMaxSize:          prefixBatchMaxSize,
+		tableChangesPerWrite:  maxTableChangesPerWrite,
+		originChangesPerWrite: maxOriginChangesPerWrite,
+		heldBack:              make(map[string][]*ristypes.RISMessage),
+		tablePeersDown:        table.PeersDown,
 	}
 }
 

internal/routewatch/prefixhandler_originchanges_internal_test.go

@@ -0,0 +1,181 @@
+package routewatch
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"log/slog"
+	"net/netip"
+	"slices"
+	"testing"
+
+	"git.eeqj.de/sneak/routewatch/internal/database"
+	"git.eeqj.de/sneak/routewatch/internal/logger"
+	"git.eeqj.de/sneak/routewatch/internal/routetable"
+)
+
+// TestPrefixHandlerWritesOriginChanges hands a running prefix handler an
+// announcement and flushes. The flush must write the origin change to the
+// database.
+func TestPrefixHandlerWritesOriginChanges(t *testing.T) {
+	t.Parallel()
+
+	db := newTestDatabase(t)
+	h := prefixHandlerWithoutTimer(db)
+
+	h.HandleMessage(peerAnnouncement(testPeerIP, testV4Prefix))
+	h.flushBatch()
+
+	got, err := db.GetOriginChanges(t.Context(),
+		netip.MustParsePrefix(testV4Prefix), 10)
+	if err != nil {
+		t.Fatalf("GetOriginChanges: %v", err)
+	}
+
+	if len(got) != 1 || !got[0].Announced || got[0].OriginASN != testASNB {
+		t.Errorf("GetOriginChanges = %+v, want one announced row for AS%d",
+			got, testASNB)
+	}
+}
+
+// errTestOriginChangeWrite is the error a test store's failing write of the
+// origin changes returns.
+var errTestOriginChangeWrite = errors.New(
+	"test: the write of the origin changes failed")
+
+// originChangesFailsStore is a real database whose first write of the origin
+// changes fails, writing nothing. writes counts the writes asked for.
+type originChangesFailsStore struct {
+	*database.Database
+
+	writes int
+}
+
+func (s *originChangesFailsStore) WriteOriginChanges(
+	changes []routetable.OriginChange,
+) error {
+	s.writes++
+	if s.writes == 1 {
+		return errTestOriginChangeWrite
+	}
+
+	return s.Database.WriteOriginChanges(changes)
+}
+
+// TestPrefixHandlerWritesAFailedOriginChangeWriteAgain runs two flushes into a
+// database whose first write of the origin changes fails. The second write must
+// hold the change of the first.
+func TestPrefixHandlerWritesAFailedOriginChangeWriteAgain(t *testing.T) {
+	t.Parallel()
+
+	db := newTestDatabase(t)
+	store := &originChangesFailsStore{Database: db}
+	h := prefixHandlerWithoutTimer(store)
+
+	h.HandleMessage(peerAnnouncement(testPeerIP, testV4Prefix))
+	h.flushBatch()
+	h.flushBatch()
+
+	got, err := db.GetOriginChanges(t.Context(),
+		netip.MustParsePrefix(testV4Prefix), 10)
+	if err != nil {
+		t.Fatalf("GetOriginChanges: %v", err)
+	}
+
+	if len(got) != 1 || !got[0].Announced || got[0].OriginASN != testASNB {
+		t.Errorf("GetOriginChanges = %+v, want one announced row for AS%d",
+			got, testASNB)
+	}
+}
+
+// originChangesWriteSizesStore is a real database that records how many
+// changes each write of the origin changes holds.
+type originChangesWriteSizesStore struct {
+	*database.Database
+
+	counts []int
+}
+
+func (s *originChangesWriteSizesStore) WriteOriginChanges(
+	changes []routetable.OriginChange,
+) error {
+	s.counts = append(s.counts, len(changes))
+
+	return s.Database.WriteOriginChanges(changes)
+}
+
+// TestPrefixHandlerWritesManyOriginChangesOverSeveralFlushes has more origin
+// changes than one write takes, then flushes three times. The first write must
+// hold one write's worth, the second the rest, and the third nothing. The
+// handler's limit is small.
+func TestPrefixHandlerWritesManyOriginChangesOverSeveralFlushes(t *testing.T) {
+	t.Parallel()
+
+	const perWrite = 10
+
+	db := newTestDatabase(t)
+	store := &originChangesWriteSizesStore{Database: db}
+	h := prefixHandlerWithoutTimer(store)
+	h.originChangesPerWrite = perWrite
+
+	announceManyPrefixes(h.table, perWrite*3/2)
+
+	h.flushBatch()
+	h.flushBatch()
+	h.flushBatch()
+
+	want := []int{perWrite, perWrite*3/2 - perWrite}
+	if !slices.Equal(store.counts, want) {
+		t.Errorf("WriteOriginChanges held %v changes, want %v", store.counts, want)
+	}
+}
+
+// TestPrefixHandlerLogsTheDroppedOriginChanges fills the routing table with
+// one origin change more than it keeps, then flushes. The warning the flush
+// logs must carry the dropped count.
+func TestPrefixHandlerLogsTheDroppedOriginChanges(t *testing.T) {
+	t.Parallel()
+
+	var logs bytes.Buffer
+
+	db := newTestDatabase(t)
+	h := prefixHandlerWithoutTimer(db)
+	h.logger = &logger.Logger{
+		Logger: slog.New(slog.NewJSONHandler(&logs,
+			&slog.HandlerOptions{Level: slog.LevelWarn})),
+	}
+
+	announceManyPrefixes(h.table, routetable.MaxWaitingOriginChanges+1)
+
+	h.flushBatch()
+
+	var warning struct {
+		Msg     string `json:"msg"`
+		Dropped *int   `json:"dropped"`
+	}
+
+	found := false
+
+	for line := range bytes.SplitSeq(bytes.TrimSpace(logs.Bytes()), []byte("\n")) {
+		warning.Dropped = nil
+
+		err := json.Unmarshal(line, &warning)
+		if err != nil {
+			t.Fatalf("want a JSON log line, got %q: %v", line, err)
+		}
+
+		if warning.Msg != "Origin changes dropped" {
+			continue
+		}
+
+		found = true
+
+		if warning.Dropped == nil || *warning.Dropped != 1 {
+			t.Errorf("the warning's dropped = %v, want 1", warning.Dropped)
+		}
+	}
+
+	if !found {
+		t.Errorf("no warning logged the dropped origin changes")
+	}
+}

internal/server/handlers.go

@@ -88,6 +88,10 @@ const (
 	ipVersionV6 = 6
 )
 
+// maxOriginChangesOnPage is the most origin changes the prefix page shows. A
+// prefix with more shows the newest ones and says so.
+const maxOriginChangesOnPage = 5000
+
 // HealthCheckResponse represents the health check response.
 type HealthCheckResponse struct {
 	Status    string            `json:"status"`
@@ -1534,27 +1538,24 @@ func (s *Server) handlePrefixDetail() http.HandlerFunc {
 
 		routes := prefixRoutes(parsed, origins)
 
-		// Prepare template data
-		data := struct {
-			Prefix      string
-			MaskLength  int
-			IPVersion   int
-			Routes      []EnhancedRoute
-			Origins     []*ASNInfo
-			PeerCount   int
-			OriginCount int
-			CSPNonce    string
-		}{
-			Prefix:      parsed.String(),
-			MaskLength:  parsed.Bits(),
-			IPVersion:   ipVersionOf(parsed),
-			Routes:      routesWithASPathHandles(routes),
-			Origins:     originInfos,
-			PeerCount:   len(routes),
-			OriginCount: len(originInfos),
-			CSPNonce:    cspNonce(r.Context()),
+		changes, moreChanges, err := s.prefixOriginChanges(r.Context(), parsed)
+		if deadlinePassed(r.Context()) {
+			http.Error(w, requestTimeoutMessage, http.StatusGatewayTimeout)
+
+			return
 		}
 
+		if err != nil {
+			s.logger.Error("Failed to get the origin changes", "error", err)
+			http.Error(w, internalErrorMessage, http.StatusInternalServerError)
+
+			return
+		}
+
+		// Prepare template data
+		data := newPrefixDetailData(parsed, routes, originInfos, changes,
+			moreChanges, cspNonce(r.Context()))
+
 		// Check if context is still valid before writing response
 		select {
 		case <-r.Context().Done():
@@ -1606,6 +1607,61 @@ func (s *Server) originASNs(
 	return infos, nil
 }
 
+// prefixOriginChanges returns prefix's origin changes for the page, newest
+// first, at most maxOriginChangesOnPage, and whether there are more.
+func (s *Server) prefixOriginChanges(
+	ctx context.Context, prefix netip.Prefix,
+) ([]routetable.OriginChange, bool, error) {
+	// One more is read to know whether there are more.
+	changes, err := s.db.GetOriginChanges(ctx, prefix, maxOriginChangesOnPage+1)
+	if err != nil {
+		return nil, false, err
+	}
+
+	more := len(changes) > maxOriginChangesOnPage
+	if more {
+		changes = changes[:maxOriginChangesOnPage]
+	}
+
+	return changes, more, nil
+}
+
+// prefixDetailData is what the prefix detail page is rendered with.
+type prefixDetailData struct {
+	Prefix            string
+	MaskLength        int
+	IPVersion         int
+	Routes            []EnhancedRoute
+	Origins           []*ASNInfo
+	PeerCount         int
+	OriginCount       int
+	OriginChanges     []routetable.OriginChange
+	MoreOriginChanges bool
+	// MaxOriginChanges is the most origin changes the page shows.
+	MaxOriginChanges int
+	CSPNonce         string
+}
+
+// newPrefixDetailData builds the prefix detail page's data.
+func newPrefixDetailData(
+	parsed netip.Prefix, routes []LiveRoute, originInfos []*ASNInfo,
+	changes []routetable.OriginChange, moreChanges bool, nonce string,
+) prefixDetailData {
+	return prefixDetailData{
+		Prefix:            parsed.String(),
+		MaskLength:        parsed.Bits(),
+		IPVersion:         ipVersionOf(parsed),
+		Routes:            routesWithASPathHandles(routes),
+		Origins:           originInfos,
+		PeerCount:         len(routes),
+		OriginCount:       len(originInfos),
+		OriginChanges:     changes,
+		MoreOriginChanges: moreChanges,
+		MaxOriginChanges:  maxOriginChangesOnPage,
+		CSPNonce:          nonce,
+	}
+}
+
 // prefixRoutes returns one route for each peer that carries prefix, by origin
 // AS in the order of origins. Each origin's kept routes come first, newest
 // first, with their AS path, next hop and time. Its other peers follow without

internal/server/prefix_originchanges_internal_test.go

@@ -0,0 +1,230 @@
+package server
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"net/netip"
+	"strings"
+	"testing"
+
+	"git.eeqj.de/sneak/routewatch/internal/config"
+	"git.eeqj.de/sneak/routewatch/internal/database"
+	"git.eeqj.de/sneak/routewatch/internal/logger"
+	"git.eeqj.de/sneak/routewatch/internal/metrics"
+	"git.eeqj.de/sneak/routewatch/internal/ristypes"
+	"git.eeqj.de/sneak/routewatch/internal/routetable"
+	"git.eeqj.de/sneak/routewatch/internal/streamer"
+)
+
+// testUncarriedASN is an AS the test's routing table does not carry for the prefix.
+const testUncarriedASN = 64501
+
+// newPrefixDetailServer returns a server whose routing table holds testPrefixV4
+// with origin AS 64500, and whose database holds the given origin changes.
+func newPrefixDetailServer(
+	t *testing.T, changes []routetable.OriginChange,
+) *Server {
+	t.Helper()
+
+	db, err := database.New(&config.Config{StateDir: t.TempDir()}, logger.New())
+	if err != nil {
+		t.Fatalf("database.New: %v", err)
+	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	table := emptyTable()
+	announce(table, testPrefixV4, 64500, testPeer(1), testRouteTime(0))
+
+	err = db.WriteOriginChanges(changes)
+	if err != nil {
+		t.Fatalf("WriteOriginChanges: %v", err)
+	}
+
+	return New(db, table, streamer.New(logger.New(), metrics.New()),
+		logger.New(), &config.Config{})
+}
+
+// TestPrefixDetailShowsOriginChanges checks that the prefix page shows the
+// origin changes newest first, with the announced and withdrawn rows and the
+// AS link. The rows use an AS the routing table does not carry for the
+// prefix, so the link comes from the origin changes table.
+func TestPrefixDetailShowsOriginChanges(t *testing.T) {
+	t.Parallel()
+
+	prefix := netip.MustParsePrefix(testPrefixV4)
+
+	s := newPrefixDetailServer(t, []routetable.OriginChange{
+		{Prefix: prefix, OriginASN: testUncarriedASN, Announced: true,
+			PeerCount: 1, Time: testRouteTime(1)},
+		{Prefix: prefix, OriginASN: testUncarriedASN, Announced: false,
+			PeerCount: 0, Time: testRouteTime(2)},
+	})
+
+	rec := httptest.NewRecorder()
+	s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/prefix/"+testPrefixV4, nil))
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status %d, want %d; body %s", rec.Code, http.StatusOK, rec.Body)
+	}
+
+	page := rec.Body.String()
+
+	withdrawn := strings.Index(page, "Withdrawn")
+	announced := strings.Index(page, "Announced")
+
+	if withdrawn < 0 || announced < 0 {
+		t.Fatalf("page does not show the announced and withdrawn rows")
+	}
+
+	// The withdrawn row is newer, so it comes first.
+	if withdrawn > announced {
+		t.Errorf("the withdrawn row is not shown before the announced row")
+	}
+
+	if !strings.Contains(page, `href="/as/64501"`) {
+		t.Errorf("page does not link to AS64501")
+	}
+}
+
+// TestPrefixDetailShowsOriginZeroAsNoKnownOrigin checks that the origin
+// changes table shows AS 0 as no known origin, without a link to AS0.
+func TestPrefixDetailShowsOriginZeroAsNoKnownOrigin(t *testing.T) {
+	t.Parallel()
+
+	prefix := netip.MustParsePrefix(testPrefixV4)
+
+	s := newPrefixDetailServer(t, []routetable.OriginChange{
+		{Prefix: prefix, OriginASN: ristypes.NoOrigin, Announced: true,
+			PeerCount: 1, Time: testRouteTime(1)},
+	})
+
+	rec := httptest.NewRecorder()
+	s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/prefix/"+testPrefixV4, nil))
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status %d, want %d; body %s", rec.Code, http.StatusOK, rec.Body)
+	}
+
+	page := rec.Body.String()
+
+	if !strings.Contains(page, "No known origin") {
+		t.Errorf("page does not say the origin change has no known origin")
+	}
+
+	if strings.Contains(page, `href="/as/0"`) {
+		t.Errorf("page links to AS0")
+	}
+}
+
+// TestPrefixDetailSaysWhenThereAreMoreChangesThanItShows checks that the
+// prefix page says so when a prefix has more origin changes than the page's
+// limit.
+func TestPrefixDetailSaysWhenThereAreMoreChangesThanItShows(t *testing.T) {
+	t.Parallel()
+
+	prefix := netip.MustParsePrefix(testPrefixV4)
+
+	changes := make([]routetable.OriginChange, 0, maxOriginChangesOnPage+1)
+	for i := range maxOriginChangesOnPage + 1 {
+		changes = append(changes, routetable.OriginChange{
+			Prefix: prefix, OriginASN: 64500, Announced: true, PeerCount: 1,
+			Time: testRouteTime(i),
+		})
+	}
+
+	s := newPrefixDetailServer(t, changes)
+
+	rec := httptest.NewRecorder()
+	s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/prefix/"+testPrefixV4, nil))
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status %d, want %d; body %s", rec.Code, http.StatusOK, rec.Body)
+	}
+
+	page := rec.Body.String()
+
+	note := fmt.Sprintf("more than %d changes", maxOriginChangesOnPage)
+	if !strings.Contains(page, note) {
+		t.Errorf("page does not say there are more than %d changes",
+			maxOriginChangesOnPage)
+	}
+
+	if got := strings.Count(page, "<td>Announced</td>"); got != maxOriginChangesOnPage {
+		t.Errorf("page shows %d change rows, want %d", got,
+			maxOriginChangesOnPage)
+	}
+}
+
+// TestPrefixDetailShowsNoNoteAtTheLimit checks that a prefix with exactly the
+// page's limit of origin changes shows all of them and no note.
+func TestPrefixDetailShowsNoNoteAtTheLimit(t *testing.T) {
+	t.Parallel()
+
+	prefix := netip.MustParsePrefix(testPrefixV4)
+
+	changes := make([]routetable.OriginChange, 0, maxOriginChangesOnPage)
+	for i := range maxOriginChangesOnPage {
+		changes = append(changes, routetable.OriginChange{
+			Prefix: prefix, OriginASN: 64500, Announced: true, PeerCount: 1,
+			Time: testRouteTime(i),
+		})
+	}
+
+	s := newPrefixDetailServer(t, changes)
+
+	rec := httptest.NewRecorder()
+	s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/prefix/"+testPrefixV4, nil))
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status %d, want %d; body %s", rec.Code, http.StatusOK, rec.Body)
+	}
+
+	page := rec.Body.String()
+
+	if strings.Contains(page, "more than") {
+		t.Errorf("page says there are more changes, but a prefix has %d",
+			maxOriginChangesOnPage)
+	}
+
+	if got := strings.Count(page, "<td>Announced</td>"); got != maxOriginChangesOnPage {
+		t.Errorf("page shows %d change rows, want %d", got,
+			maxOriginChangesOnPage)
+	}
+}
+
+// TestPrefixDetailShowsOriginChangeTimeAndPeerCount checks that a row shows
+// its time and its peer count.
+func TestPrefixDetailShowsOriginChangeTimeAndPeerCount(t *testing.T) {
+	t.Parallel()
+
+	prefix := netip.MustParsePrefix(testPrefixV4)
+
+	s := newPrefixDetailServer(t, []routetable.OriginChange{
+		{Prefix: prefix, OriginASN: 64500, Announced: true, PeerCount: 7,
+			Time: testRouteTime(5)},
+	})
+
+	rec := httptest.NewRecorder()
+	s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/prefix/"+testPrefixV4, nil))
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status %d, want %d; body %s", rec.Code, http.StatusOK, rec.Body)
+	}
+
+	page := rec.Body.String()
+
+	if !strings.Contains(page, "2026-01-02 03:09:05") {
+		t.Errorf("page does not show the origin change's time")
+	}
+
+	if !strings.Contains(page, "<td>7</td>") {
+		t.Errorf("page does not show the origin change's peer count")
+	}
+}

internal/server/server.go

@@ -7,8 +7,8 @@
 //   - the AS name search
 //
 // Every route it shows comes from the routing table in memory. AS names,
-// WHOIS details and the times a prefix and an AS were first seen come from
-// the database.
+// WHOIS details, the times a prefix and an AS were first seen, and a prefix's
+// origin changes come from the database.
 package server
 
 import (

internal/templates/prefix_detail.html

@@ -299,6 +299,41 @@
         </div>
         {{end}}
 
+        {{if .OriginChanges}}
+        <div class="origins-section">
+            <h3>Origin Changes</h3>
+            {{if .MoreOriginChanges}}
+            <p>There are more than {{.MaxOriginChanges}} changes. Showing the newest {{.MaxOriginChanges}}.</p>
+            {{end}}
+            <table class="route-table">
+                <thead>
+                    <tr>
+                        <th>Time (UTC)</th>
+                        <th>Change</th>
+                        <th>Origin AS</th>
+                        <th>Peers</th>
+                    </tr>
+                </thead>
+                <tbody>
+                    {{range .OriginChanges}}
+                    <tr>
+                        <td>{{.Time.Format "2006-01-02 15:04:05"}}</td>
+                        <td>{{if .Announced}}Announced{{else}}Withdrawn{{end}}</td>
+                        <td>
+                            {{if .OriginASN}}
+                            <a href="/as/{{.OriginASN}}" class="as-link">AS{{.OriginASN}}</a>
+                            {{else}}
+                            No known origin
+                            {{end}}
+                        </td>
+                        <td>{{.PeerCount}}</td>
+                    </tr>
+                    {{end}}
+                </tbody>
+            </table>
+        </div>
+        {{end}}
+
         {{if .Routes}}
         <div class="routes-section">
             <div class="routes-header">