From 1e55b7987f0252706adc1412edb0546e9065d285 Mon Sep 17 00:00:00 2001
From: Fabian Reinartz <fab.reinartz@gmail.com>
Date: Fri, 22 Dec 2017 09:43:34 +0100
Subject: [PATCH] Improve comments, handle allPostingsKey properly

---
 block.go          |  6 +++---
 chunks/chunks.go  |  3 ---
 compact.go        |  2 +-
 index/postings.go | 16 +++++++++++++---
 querier.go        |  3 +--
 5 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/block.go b/block.go
index 4ef58e913..400cdac78 100644
--- a/block.go
+++ b/block.go
@@ -63,7 +63,7 @@ type IndexReader interface {
 	// and indices.
 	Symbols() (map[string]struct{}, error)
 
-	// LabelValues returns the possible label values
+	// LabelValues returns the possible label values.
 	LabelValues(names ...string) (index.StringTuples, error)
 
 	// Postings returns the postings list iterator for the label pair.
@@ -81,10 +81,10 @@ type IndexReader interface {
 	// Returns ErrNotFound if the ref does not resolve to a known series.
 	Series(ref uint64, lset *labels.Labels, chks *[]chunks.Meta) error
 
-	// LabelIndices returns the label pairs for which indices exist.
+	// LabelIndices returns a list of string tuples for which a label value index exists.
 	LabelIndices() ([][]string, error)
 
-	// Close released the underlying resources of the reader.
+	// Close releases the underlying resources of the reader.
 	Close() error
 }
 
diff --git a/chunks/chunks.go b/chunks/chunks.go
index d07cf11a6..e32ea0f99 100644
--- a/chunks/chunks.go
+++ b/chunks/chunks.go
@@ -63,9 +63,6 @@ var (
 	errInvalidChecksum = fmt.Errorf("invalid checksum")
 )
 
-// The table gets initialized with sync.Once but may still cause a race
-// with any other use of the crc32 package anywhere. Thus we initialize it
-// before.
 var castagnoliTable *crc32.Table
 
 func init() {
diff --git a/compact.go b/compact.go
index 9a73ca07b..5c532759f 100644
--- a/compact.go
+++ b/compact.go
@@ -516,7 +516,7 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 			allSymbols[s] = struct{}{}
 		}
 
-		all, err := indexr.Postings("", "")
+		all, err := indexr.Postings(index.AllPostingsKey())
 		if err != nil {
 			return err
 		}
diff --git a/index/postings.go b/index/postings.go
index bc63b4dac..f942edaad 100644
--- a/index/postings.go
+++ b/index/postings.go
@@ -23,6 +23,13 @@ import (
 	"github.com/prometheus/tsdb/labels"
 )
 
+var allPostingsKey = labels.Label{}
+
+// AllPostingsKey returns the label key that is used to store the postings list of all existing IDs.
+func AllPostingsKey() (name, value string) {
+	return allPostingsKey.Name, allPostingsKey.Value
+}
+
 // MemPostings holds postings list for series ID per label pair. They may be written
 // to out of order.
 // ensureOrder() must be called once before any reads are done. This allows for quick
@@ -83,11 +90,9 @@ func (p *MemPostings) Get(name, value string) Postings {
 
 // All returns a postings list over all documents ever added.
 func (p *MemPostings) All() Postings {
-	return p.Get(allPostingsKey.Name, allPostingsKey.Value)
+	return p.Get(AllPostingsKey())
 }
 
-var allPostingsKey = labels.Label{}
-
 // EnsureOrder ensures that all postings lists are sorted. After it returns all further
 // calls to add and addFor will insert new IDs in a sorted manner.
 func (p *MemPostings) EnsureOrder() {
@@ -126,13 +131,18 @@ func (p *MemPostings) EnsureOrder() {
 func (p *MemPostings) Delete(deleted map[uint64]struct{}) {
 	var keys []labels.Label
 
+	// Collect all keys relevant for deletion once. New keys added afterwards
+	// can by definition not be affected by any of the given deletes.
 	p.mtx.RLock()
 	for l := range p.m {
 		keys = append(keys, l)
 	}
 	p.mtx.RUnlock()
 
+	// For each key we first analyse whether the postings list is affected by the deletes.
+	// If yes, we actually reallocate a new postings list.
 	for _, l := range keys {
+		// Only lock for processing one postings list so we don't block reads for too long.
 		p.mtx.Lock()
 
 		found := false
diff --git a/querier.go b/querier.go
index 48d7ba9c2..d4dad9306 100644
--- a/querier.go
+++ b/querier.go
@@ -334,11 +334,10 @@ func postingsForUnsetLabelMatcher(ix IndexReader, m labels.Matcher) (index.Posti
 		rit = append(rit, it)
 	}
 
-	allPostings, err := ix.Postings("", "")
+	allPostings, err := ix.Postings(index.AllPostingsKey())
 	if err != nil {
 		return nil, err
 	}
-
 	return index.Without(allPostings, index.Merge(rit...)), nil
 }