From e068c7332d3a2cb23ac9f291b848a3f3d36f3bee Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Tue, 5 Aug 2025 13:09:29 +0100
Subject: [PATCH] [REFACTOR] TSDB: Clarify intersectPostings

This is intended to make `intersectPostings` easier to follow.

Instead of cryptic `arr` and `cur`, name the members `postings` and
`current`.

Instead of updating `cur` to intermediate values encountered during
operations, introduce a local variable `target` meaning the ref we might
expect to find next, and only update `current` when an intersection is
found.

Name the function which implements seeking `Seek` instead of `doNext`.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
---
 tsdb/index/postings.go | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

diff --git a/tsdb/index/postings.go b/tsdb/index/postings.go
index 98369e3326..223b01b012 100644
--- a/tsdb/index/postings.go
+++ b/tsdb/index/postings.go
@@ -607,57 +607,54 @@ func Intersect(its ...Postings) Postings {
 }
 
 type intersectPostings struct {
-	arr []Postings
-	cur storage.SeriesRef
+	postings []Postings        // These are the postings we will be intersecting.
+	current  storage.SeriesRef // The current intersection, if Seek() or Next() has returned true.
 }
 
 func newIntersectPostings(its ...Postings) *intersectPostings {
-	return &intersectPostings{arr: its}
+	return &intersectPostings{postings: its}
 }
 
 func (it *intersectPostings) At() storage.SeriesRef {
-	return it.cur
+	return it.current
 }
 
-func (it *intersectPostings) doNext() bool {
+func (it *intersectPostings) Seek(target storage.SeriesRef) bool {
 	for {
 		allEqual := true
-		for _, p := range it.arr {
-			if !p.Seek(it.cur) {
+		for _, p := range it.postings {
+			if !p.Seek(target) {
 				return false
 			}
-			if p.At() > it.cur {
-				it.cur = p.At()
+			if p.At() > target {
+				target = p.At()
 				allEqual = false
 			}
 		}
 
 		// if all p.At() are all equal, we found an intersection.
 		if allEqual {
+			it.current = target
 			return true
 		}
 	}
 }
 
 func (it *intersectPostings) Next() bool {
-	for _, p := range it.arr {
+	target := it.current
+	for _, p := range it.postings {
 		if !p.Next() {
 			return false
 		}
-		if p.At() > it.cur {
-			it.cur = p.At()
+		if p.At() > target {
+			target = p.At()
 		}
 	}
-	return it.doNext()
-}
-
-func (it *intersectPostings) Seek(id storage.SeriesRef) bool {
-	it.cur = id
-	return it.doNext()
+	return it.Seek(target)
 }
 
 func (it *intersectPostings) Err() error {
-	for _, p := range it.arr {
+	for _, p := range it.postings {
 		if p.Err() != nil {
 			return p.Err()
 		}