README.md

@@ -142,7 +142,11 @@ 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: each time an origin
+  AS gained its first peer or lost its last, with the time, announced or
+  withdrawn, the origin AS and the peer count. It shows at most the newest
+  5,000.
 - `/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 +520,8 @@ 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
@@ -638,7 +643,7 @@ 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.
 - 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
@@ -809,6 +814,10 @@ 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
+One question waits for sneak: which fields the IP lookup answer gains
-(https://git.eeqj.de/sneak/routewatch/issues/161), and which fields the IP
+(https://git.eeqj.de/sneak/routewatch/issues/203).
-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 +56,13 @@ problem the run finds.
 
 # Completed Steps
 
+- 2026-11-05: the prefix page lists the prefix's origin changes, newest first:
+  each time an origin AS gained its first peer or lost its last, with the time,
+  announced or withdrawn, the origin AS and the peer count. 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 and 72 hours. The page shows at most the newest 5,000 (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

@@ -55,6 +55,14 @@ 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"
+)
+
+// maxOriginChangesPerPrefix is how many origin changes the prune keeps for
+// each prefix: the newest ones. A prefix with more has its older rows deleted.
+const maxOriginChangesPerPrefix = 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
+// maxOriginChangesPerPrefix.
+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
+// maxOriginChangesPerPrefix rows, the rows older than originChangesRetention
+// that are not among its newest maxOriginChangesPerPrefix. 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,
+		maxOriginChangesPerPrefix)
+	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, maxOriginChangesPerPrefix-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 +1,160 @@
+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 every row newer than 72
+// hours, keeps the newest 500 rows of each prefix, deletes the rest, and
+// leaves other prefixes alone.
+func TestOriginChangesPrune(t *testing.T) {
+	t.Parallel()
+
+	db := newRoutesTestDatabase(t)
+	oldPrefix := netip.MustParsePrefix(tablePrefixV4)
+	newPrefix := netip.MustParsePrefix(tablePrefixShortV4)
+	other := netip.MustParsePrefix("10.20.0.0/16")
+
+	now := time.Now()
+
+	changes := make([]routetable.OriginChange, 0, 1201)
+
+	// 600 rows for oldPrefix, all older than 72 hours, oldest first. The
+	// prune keeps the newest 500 and deletes the oldest 100.
+	for i := range 600 {
+		changes = append(changes, routetable.OriginChange{
+			Prefix: oldPrefix, OriginASN: asA, Announced: true, PeerCount: 1,
+			Time: now.Add(-100 * time.Hour).Add(time.Duration(i) * time.Minute),
+		})
+	}
+
+	// 600 rows for newPrefix, all newer than 72 hours, oldest first. The
+	// prune keeps all of them.
+	for i := range 600 {
+		changes = append(changes, routetable.OriginChange{
+			Prefix: newPrefix, OriginASN: asA, Announced: true, PeerCount: 1,
+			Time: now.Add(-71 * time.Hour).Add(time.Duration(i) * time.Minute),
+		})
+	}
+
+	// One row for other, which the prune leaves alone.
+	changes = append(changes, routetable.OriginChange{
+		Prefix: other, OriginASN: asA, Announced: true, PeerCount: 1,
+		Time: now.Add(-100 * time.Hour),
+	})
+
+	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)
+	}
+
+	gotOld, err := db.GetOriginChanges(t.Context(), oldPrefix, 1000)
+	if err != nil {
+		t.Fatalf("GetOriginChanges: %v", err)
+	}
+
+	if len(gotOld) != 500 {
+		t.Errorf("GetOriginChanges(oldPrefix) = %d rows, want 500", len(gotOld))
+	}
+
+	gotNew, err := db.GetOriginChanges(t.Context(), newPrefix, 1000)
+	if err != nil {
+		t.Fatalf("GetOriginChanges: %v", err)
+	}
+
+	if len(gotNew) != 600 {
+		t.Errorf("GetOriginChanges(newPrefix) = %d rows, want 600", len(gotNew))
+	}
+
+	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))
+	}
+}
+
+// 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/schema.sql

@@ -120,3 +120,18 @@ 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 and 72
+-- hours. 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 +1,88 @@
+package routetable
+
+import (
+	"net/netip"
+	"slices"
+	"time"
+)
+
+// maxWaitingOriginChanges is the most origin changes the table keeps waiting
+// for the prefix handler to write. A 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(),
+	}
+
+	if len(t.originChanges) == maxWaitingOriginChanges {
+		// The oldest change is dropped to make room.
+		t.originChanges = t.originChanges[1:]
+		t.originChangesDropped++
+	}
+
+	t.originChanges = append(t.originChanges, change)
+}
+
+// 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.
+func (t *Table) PutBackOriginChanges(changes []OriginChange) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	t.originChanges = append(changes, 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 +1,224 @@
+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()
+
+	const limit = 100000
+
+	table := routetable.New(routetable.Params{})
+	addr := netip.MustParseAddr("10.0.0.0")
+
+	for range limit + 1 {
+		prefix := netip.PrefixFrom(addr, 32)
+		table.Announce(prefix, asA, routeOf(peerA, asA, 10))
+
+		addr = addr.Next()
+	}
+
+	changes, dropped := table.TakeOriginChanges(limit)
+	if dropped != 1 {
+		t.Errorf("dropped = %d, want 1", dropped)
+	}
+
+	if len(changes) != limit {
+		t.Errorf("len(changes) = %d, want %d", len(changes), limit)
+	}
+}
+
+// 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)
 		}),
@@ -469,6 +488,8 @@ 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 +503,10 @@ 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
@@ -549,6 +574,7 @@ 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/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
@@ -111,6 +118,9 @@ 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 +137,10 @@ 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 +189,18 @@ 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
@@ -507,6 +511,7 @@ func (h *PrefixHandler) takeBatch() []seenPrefix {
 // writes.
 func (h *PrefixHandler) flushBatch() {
 	h.writeTableChanges()
+	h.writeOriginChanges()
 
 	batch := h.takeBatch()
 	if len(batch) == 0 {
@@ -608,6 +613,30 @@ func (h *PrefixHandler) writeTableChanges() {
 	}
 }
 
+// writeOriginChanges writes at most maxOriginChangesPerWrite 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() {
+	changes, dropped := h.table.TakeOriginChanges(maxOriginChangesPerWrite)
+
+	if dropped > 0 {
+		h.logger.Warn("Origin changes dropped", "dropped", dropped)
+	}
+
+	if len(changes) == 0 {
+		return
+	}
+
+	err := h.db.WriteOriginChanges(changes)
+	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_originchanges_internal_test.go

@@ -0,0 +1,84 @@
+package routewatch
+
+import (
+	"errors"
+	"net/netip"
+	"testing"
+
+	"git.eeqj.de/sneak/routewatch/internal/database"
+	"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)
+	}
+}

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
+		changes, moreChanges, err := s.prefixOriginChanges(r.Context(), parsed)
-		data := struct {
+		if deadlinePassed(r.Context()) {
-			Prefix      string
+			http.Error(w, requestTimeoutMessage, http.StatusGatewayTimeout)
-			MaskLength  int
+
-			IPVersion   int
+			return
-			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()),
 		}
 
+		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 +1607,58 @@ 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
+	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,
+		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 +1,148 @@
+package server
+
+import (
+	"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"
+)
+
+// 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.
+func TestPrefixDetailShowsOriginChanges(t *testing.T) {
+	t.Parallel()
+
+	prefix := netip.MustParsePrefix(testPrefixV4)
+
+	s := newPrefixDetailServer(t, []routetable.OriginChange{
+		{Prefix: prefix, OriginASN: 64500, Announced: true, PeerCount: 1,
+			Time: testRouteTime(1)},
+		{Prefix: prefix, OriginASN: 64500, 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/64500"`) {
+		t.Errorf("page does not link to AS64500")
+	}
+}
+
+// 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")
+	}
+}
+
+// TestPrefixDetailSaysWhenMoreThan5000Changes checks that the prefix page says
+// so when a prefix has more than 5,000 origin changes.
+func TestPrefixDetailSaysWhenMoreThan5000Changes(t *testing.T) {
+	t.Parallel()
+
+	prefix := netip.MustParsePrefix(testPrefixV4)
+
+	changes := make([]routetable.OriginChange, 0, 5001)
+	for i := range 5001 {
+		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 5,000 changes") {
+		t.Errorf("page does not say there are more than 5,000 changes")
+	}
+}

internal/templates/prefix_detail.html

@@ -297,6 +297,41 @@
                 {{end}}
             </div>
         </div>
+{{end}}
+
+        {{if .OriginChanges}}
+        <div class="origins-section">
+            <h3>Origin Changes</h3>
+            {{if .MoreOriginChanges}}
+            <p>There are more than 5,000 changes. Showing the newest 5,000.</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}}