From 165d9a534e27be3f53903e7ec5c1d8557c0f11ea Mon Sep 17 00:00:00 2001
From: Thejas-bhat <thejas.orkombu@couchbase.com>
Date: Wed, 9 Aug 2023 11:47:31 +0530
Subject: [PATCH] implementing the Count() API for the postings list, updated
 todos

---
 build.go                |  2 +-
 section_vector_index.go |  4 ++++
 vector_search.go        | 12 ++++++++++--
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/build.go b/build.go
index d9aadadd..d5686bfd 100644
--- a/build.go
+++ b/build.go
@@ -24,7 +24,7 @@ import (
 	"github.com/blevesearch/vellum"
 )
 
-const Version uint32 = 16
+const Version uint32 = 15
 
 const Type string = "zap"
 
diff --git a/section_vector_index.go b/section_vector_index.go
index d12ce49e..7d7673e8 100644
--- a/section_vector_index.go
+++ b/section_vector_index.go
@@ -141,6 +141,10 @@ func (vo *vectorIndexOpaque) writeVectorIndexes(w *CountHashWriter) (offset uint
 
 		// fixme: this can cause a write amplification. need to improve this.
 		// todo: might need to a reformating to optimize according to mmap needs.
+		// reformating idea: storing all the IDs mapping towards the end of the
+		// section would be help avoiding in paging in this data as part of a page
+		// (which is to load a non-cacheable info like index). this could help the
+		// paging costs
 		for vecID, docIDs := range docIDsMap {
 			// write the vecID
 			_, err := writeUvarints(w, vecID)
diff --git a/vector_search.go b/vector_search.go
index 2ccb4f10..1b6d0f72 100644
--- a/vector_search.go
+++ b/vector_search.go
@@ -36,6 +36,9 @@ func (vp *VecPosting) Size() int {
 // the score is actually a float32 value and in order to store it as a uint32 in
 // the bitmap, we use the IEEE 754 floating point format.
 type VecPostingsList struct {
+	// todo: perhaps we don't even need to store a bitmap if there is only
+	// one similar vector the query, but rather store it as a field value
+	// in the struct
 	except   *roaring64.Bitmap
 	postings *roaring64.Bitmap
 }
@@ -90,8 +93,13 @@ func (vpl *VecPostingsList) Size() int {
 	return 0
 }
 
-func (vpl *VecPostingsList) Count() uint64 {
-	return 0
+func (p *VecPostingsList) Count() uint64 {
+	n := p.postings.GetCardinality()
+	var e uint64
+	if p.except != nil {
+		e = p.postings.AndCardinality(p.except)
+	}
+	return n - e
 }
 
 func (vpl *VecPostingsList) ResetBytesRead(val uint64) {