From f8c745340ff467983f840e682d7ff4601b39be3a Mon Sep 17 00:00:00 2001
From: Travis Turner <travis@pilosa.com>
Date: Mon, 10 Sep 2018 16:56:33 -0500
Subject: [PATCH] stop tracking existence if the existence field is deleted

---
 fragment_internal_test.go |  4 ++--
 index.go                  | 12 +++++++++++
 index_internal_test.go    | 44 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 57 insertions(+), 3 deletions(-)

diff --git a/fragment_internal_test.go b/fragment_internal_test.go
index c85b7e88c..a0d1354ba 100644
--- a/fragment_internal_test.go
+++ b/fragment_internal_test.go
@@ -746,7 +746,7 @@ func TestFragment_TopN_CacheSize(t *testing.T) {
 	cacheSize := uint32(3)
 
 	// Create Index.
-	index := mustOpenIndex()
+	index := mustOpenIndex(IndexOptions{})
 	defer index.Close()
 
 	// Create field.
@@ -912,7 +912,7 @@ func TestFragment_LRUCache_Persistence(t *testing.T) {
 
 // Ensure a fragment's cache can be persisted between restarts.
 func TestFragment_RankCache_Persistence(t *testing.T) {
-	index := mustOpenIndex()
+	index := mustOpenIndex(IndexOptions{})
 	defer index.Close()
 
 	// Create field.
diff --git a/index.go b/index.go
index a78fd8365..34ab01b28 100644
--- a/index.go
+++ b/index.go
@@ -421,6 +421,18 @@ func (i *Index) DeleteField(name string) error {
 		return errors.Wrap(err, "removing directory")
 	}
 
+	// If the field being deleted is the existence field,
+	// turn off existence tracking on the index.
+	if name == existenceFieldName {
+		i.trackExistence = false
+		i.existenceField = nil
+
+		// Update meta data on disk.
+		if err := i.saveMeta(); err != nil {
+			return errors.Wrap(err, "saving existence meta data")
+		}
+	}
+
 	// Remove reference.
 	delete(i.fields, name)
 
diff --git a/index_internal_test.go b/index_internal_test.go
index 1e6d592ab..de4368d2a 100644
--- a/index_internal_test.go
+++ b/index_internal_test.go
@@ -16,10 +16,11 @@ package pilosa
 
 import (
 	"io/ioutil"
+	"testing"
 )
 
 // mustOpenIndex returns a new, opened index at a temporary path. Panic on error.
-func mustOpenIndex() *Index {
+func mustOpenIndex(opt IndexOptions) *Index {
 	path, err := ioutil.TempDir("", "pilosa-index-")
 	if err != nil {
 		panic(err)
@@ -28,6 +29,10 @@ func mustOpenIndex() *Index {
 	if err != nil {
 		panic(err)
 	}
+
+	index.keys = opt.Keys
+	index.trackExistence = opt.TrackExistence
+
 	if err := index.Open(); err != nil {
 		panic(err)
 	}
@@ -44,3 +49,40 @@ func (i *Index) reopen() error {
 	}
 	return nil
 }
+
+// Ensure that deleting the existence field is handled properly.
+func TestIndex_Existence_Delete(t *testing.T) {
+	// Create Index (with existence tracking).
+	index := mustOpenIndex(IndexOptions{TrackExistence: true})
+	defer index.Close()
+
+	// Ensure existence field has been created.
+	ef := index.Field(existenceFieldName)
+	if ef == nil {
+		t.Fatalf("expected field to have been created: %s", existenceFieldName)
+	} else if !index.trackExistence {
+		t.Fatalf("expected index.trackExistence to be true")
+	} else if index.existenceField == nil {
+		t.Fatalf("expected index.existenceField to be non-nil")
+	}
+
+	// Delete existence field.
+	if err := index.DeleteField(existenceFieldName); err != nil {
+		t.Fatal(err)
+	}
+
+	// Re-open index.
+	if err := index.reopen(); err != nil {
+		t.Fatal(err)
+	}
+
+	// Ensure existence field no longer exists.
+	ef = index.Field(existenceFieldName)
+	if ef != nil {
+		t.Fatalf("expected field to have been deleted: %s", existenceFieldName)
+	} else if index.trackExistence {
+		t.Fatalf("expected index.trackExistence to be false")
+	} else if index.existenceField != nil {
+		t.Fatalf("expected index.existenceField to be nil")
+	}
+}