radio: make SongStorage.LastPlayed use a from-key

This switches the LastPlayed pagination from limit/offset to keyset
pagination which should help performance.

ircbot/commands_impl.go

@@ -66,7 +66,7 @@ func NowPlaying(e Event) error {
 func LastPlayed(e Event) error {
 	const op errors.Op = "irc/LastPlayed"
 
-	songs, err := e.Storage.Song(e.Ctx).LastPlayed(0, 5)
+	songs, err := e.Storage.Song(e.Ctx).LastPlayed(radio.LPKeyLast, 5)
 	if err != nil {
 		return errors.E(op, err)
 	}
@@ -230,7 +230,23 @@ func FaveTrack(e Event) error {
 
 		// count the amount of `last`'s used to determine how far back we should go
 		index := strings.Count(e.Arguments["relative"], "last") - 1
-		songs, err := ss.LastPlayed(int64(index), 1)
+
+		key := radio.LPKeyLast
+		if index > 0 {
+			// if our index is higher than 0 we need to lookup the key for that
+			prev, _, err := ss.LastPlayedPagination(radio.LPKeyLast, 1, 50)
+			if err != nil {
+				return errors.E(op, err)
+			}
+			// make sure our index exists in the list
+			if index >= len(prev) {
+				return errors.E(op, "index too far")
+			}
+
+			key = prev[index]
+		}
+
+		songs, err := ss.LastPlayed(key, 1)
 		if err != nil {
 			return errors.E(op, err)
 		}

radio.go

@@ -804,6 +804,10 @@ type SongStorageService interface {
 	SongTx(context.Context, StorageTx) (SongStorage, StorageTx, error)
 }
 
+type LastPlayedKey uint32
+
+const LPKeyLast = LastPlayedKey(math.MaxUint32)
+
 // SongStorage stores information about songs
 //
 // A song can be anything that plays on stream, unlike a track which is a specific
@@ -818,7 +822,9 @@ type SongStorage interface {
 
 	// LastPlayed returns songs that have recently played, up to amount given after
 	// applying the offset
-	LastPlayed(offset, amount int64) ([]Song, error)
+	LastPlayed(key LastPlayedKey, amountPerPage int) ([]Song, error)
+	// LastPlayedPagination looks up keys for adjacent pages of key
+	LastPlayedPagination(key LastPlayedKey, amountPerPage, pageCount int) (prev, next []LastPlayedKey, err error)
 	// LastPlayedCount returns the amount of plays recorded
 	LastPlayedCount() (int64, error)
 	// PlayedCount returns the amount of times the song has been played on stream

storage/mariadb/track.go

@@ -2,11 +2,13 @@ package mariadb
 
 import (
 	"database/sql"
+	"slices"
 	"strings"
 	"time"
 
 	radio "github.com/R-a-dio/valkyrie"
 	"github.com/R-a-dio/valkyrie/errors"
+	"github.com/R-a-dio/valkyrie/util"
 	"github.com/go-sql-driver/mysql"
 	"github.com/jmoiron/sqlx"
 )
@@ -234,20 +236,22 @@ LEFT JOIN
 	users ON djs.id = users.djid
 LEFT JOIN
 	themes ON djs.theme_id = themes.id
+WHERE
+	eplay.id < ?
 ORDER BY
 	eplay.dt DESC, eplay.id DESC
-LIMIT ? OFFSET ?;
+LIMIT ?;
 `)
 
 // LastPlayed implements radio.SongStorage
-func (ss SongStorage) LastPlayed(offset, amount int64) ([]radio.Song, error) {
+func (ss SongStorage) LastPlayed(key radio.LastPlayedKey, amountPerPage int) ([]radio.Song, error) {
 	const op errors.Op = "mariadb/SongStorage.LastPlayed"
 	handle, deferFn := ss.handle.span(op)
 	defer deferFn()
 
-	var songs = make([]radio.Song, 0, amount)
+	var songs = make([]radio.Song, 0, amountPerPage)
 
-	err := sqlx.Select(handle, &songs, songLastPlayedQuery, amount, offset)
+	err := sqlx.Select(handle, &songs, songLastPlayedQuery, key, amountPerPage)
 	if err != nil {
 		return nil, errors.E(op, err)
 	}
@@ -264,6 +268,60 @@ func (ss SongStorage) LastPlayed(offset, amount int64) ([]radio.Song, error) {
 	return songs, nil
 }
 
+func (ss SongStorage) LastPlayedPagination(key radio.LastPlayedKey, amountPerPage, pageCount int) (prev, next []radio.LastPlayedKey, err error) {
+	const op errors.Op = "mariadb/SongStorage.LastPlayedPagination"
+	handle, deferFn := ss.handle.span(op)
+	defer deferFn()
+
+	total := amountPerPage * pageCount
+	tmp := make([]radio.LastPlayedKey, 0, total)
+
+	query := `
+		SELECT
+			id
+		FROM
+			eplay
+		WHERE
+			id < ?
+		ORDER BY
+			dt DESC, id DESC
+		LIMIT ?;
+	`
+
+	err = sqlx.Select(handle, &tmp, query, key, total)
+	if err != nil {
+		return nil, nil, errors.E(op, err)
+	}
+	// reduce to just the page boundaries
+	next = util.ReduceWithStep(tmp, amountPerPage)
+
+	// reset tmp for the next set
+	tmp = tmp[:0]
+	query = `
+	SELECT
+		id
+	FROM
+		eplay
+	WHERE
+		id >= ?
+	ORDER BY
+		dt ASC, id ASC
+	LIMIT ?;
+	`
+
+	err = sqlx.Select(handle, &tmp, query, key, total)
+	if err != nil {
+		return nil, nil, errors.E(op, err)
+	}
+
+	// reduce to just the page boundaries
+	prev = util.ReduceWithStep(tmp, amountPerPage)
+	// reverse since they're in ascending order
+	slices.Reverse(prev)
+
+	return prev, next, nil
+}
+
 // LastPlayedCount implements radio.SongStorage
 func (ss SongStorage) LastPlayedCount() (int64, error) {
 	const op errors.Op = "mariadb/SongStorage.LastPlayedCount"