From 7f2374b703e5ac779cfab3feefb8ade3fbf2487d Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Fri, 30 Sep 2022 15:31:32 +0100
Subject: [PATCH] tsdb: faster postings sort with generic slices.Sort (#11054)

Use new experimental package `golang.org/x/exp/slices`.

Some of the speedup comes from comparing SeriesRef (which is an int64)
directly rather than through an interface `.Less()` call; some comes
from exp/slices using "pattern-defeating quicksort(pdqsort)".

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
---
 go.mod                 |  1 +
 go.sum                 |  2 ++
 tsdb/index/postings.go | 12 ++----------
 3 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/go.mod b/go.mod
index 8d693cae65..6e6be80f40 100644
--- a/go.mod
+++ b/go.mod
@@ -167,6 +167,7 @@ require (
 	go.opentelemetry.io/otel/metric v0.32.0 // indirect
 	go.opentelemetry.io/proto/otlp v0.19.0 // indirect
 	golang.org/x/crypto v0.0.0-20220722155217-630584e8d5aa // indirect
+	golang.org/x/exp v0.0.0-20220722155223-a9213eeb770e
 	golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4 // indirect
 	golang.org/x/term v0.0.0-20210927222741-03fcf44c2211 // indirect
 	golang.org/x/text v0.3.7 // indirect
diff --git a/go.sum b/go.sum
index 8d1b6ef975..c765a770a3 100644
--- a/go.sum
+++ b/go.sum
@@ -915,6 +915,8 @@ golang.org/x/exp v0.0.0-20191227195350-da58074b4299/go.mod h1:2RIsYlXP63K8oxa1u0
 golang.org/x/exp v0.0.0-20200119233911-0405dc783f0a/go.mod h1:2RIsYlXP63K8oxa1u096TMicItID8zy7Y6sNkU49FU4=
 golang.org/x/exp v0.0.0-20200207192155-f17229e696bd/go.mod h1:J/WKrq2StrnmMY6+EHIKF9dgMWnmCNThgcyBT1FY9mM=
 golang.org/x/exp v0.0.0-20200224162631-6cc2880d07d6/go.mod h1:3jZMyOhIsHpP37uCMkUooju7aAi5cS1Q23tOzKc+0MU=
+golang.org/x/exp v0.0.0-20220722155223-a9213eeb770e h1:+WEEuIdZHnUeJJmEUjyYC2gfUMj69yZXw17EnHg/otA=
+golang.org/x/exp v0.0.0-20220722155223-a9213eeb770e/go.mod h1:Kr81I6Kryrl9sr8s2FK3vxD90NdsKWRuOIl2O4CvYbA=
 golang.org/x/image v0.0.0-20190227222117-0694c2d4d067/go.mod h1:kZ7UVZpmo3dzQBMxlp+ypCbDeSB+sBbTgSJuh5dn5js=
 golang.org/x/image v0.0.0-20190802002840-cff245a6509b/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
diff --git a/tsdb/index/postings.go b/tsdb/index/postings.go
index 8df2bccf67..a9898fc4a2 100644
--- a/tsdb/index/postings.go
+++ b/tsdb/index/postings.go
@@ -21,6 +21,7 @@ import (
 	"sync"
 
 	"github.com/pkg/errors"
+	"golang.org/x/exp/slices"
 
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/storage"
@@ -239,11 +240,9 @@ func (p *MemPostings) EnsureOrder() {
 
 	for i := 0; i < n; i++ {
 		go func() {
-			var sortable seriesRefSlice
 			for job := range workc {
 				for _, l := range *job {
-					sortable = l
-					sort.Sort(&sortable)
+					slices.Sort(l)
 				}
 
 				*job = (*job)[:0]
@@ -830,13 +829,6 @@ func (it *bigEndianPostings) Err() error {
 	return nil
 }
 
-// seriesRefSlice attaches the methods of sort.Interface to []storage.SeriesRef, sorting in increasing order.
-type seriesRefSlice []storage.SeriesRef
-
-func (x seriesRefSlice) Len() int           { return len(x) }
-func (x seriesRefSlice) Less(i, j int) bool { return x[i] < x[j] }
-func (x seriesRefSlice) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
-
 // FindIntersectingPostings checks the intersection of p and candidates[i] for each i in candidates,
 // if intersection is non empty, then i is added to the indexes returned.
 // Returned indexes are not sorted.