support scanning across pages

chirst · Jun 26, 2024 · bcfb5cc · bcfb5cc
1 parent e813d15
commit bcfb5cc
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Showing 3 changed files with 72 additions and 3 deletions.
diff --git a/kv/kv.go b/kv/kv.go
@@ -73,9 +73,9 @@ func (kv *KV) Get(pageNumber uint16, key []byte) ([]byte, bool, error) {
 func (kv *KV) Set(pageNumber uint16, key, value []byte) error {
 	// TODO set has some issues. One being set doesn't differentiate between
 	// insert and update which isn't very intentional. Two being set cannot
-	// perform multiple insertions in the span of one transaction since page
-	// splits pull out stale pages on subsequent inserts which causes difficult
-	// bugs.
+	// perform multiple insertions in the span of one transaction. This is
+	// because page splits pull out stale pages on subsequent inserts which
+	// causes difficult to diagnose bugs.
 	if pageNumber == pager.EMPTY_PARENT_PAGE_NUMBER {
 		return errorReservedPage
 	}
@@ -146,6 +146,8 @@ func (kv *KV) splitPage(page *pager.Page) (left, right *pager.Page) {
 	rightPage := kv.pager.NewPage()
 	rightEntries := entries[len(entries)/2:]
 	rightPage.SetEntries(rightEntries)
+	leftPage.SetRightPageNumber(rightPage.GetNumber())
+	rightPage.SetLeftPageNumber(leftPage.GetNumber())
 	return leftPage, rightPage
 }
 
@@ -262,6 +264,8 @@ type Cursor struct {
 	rootPageNumber     int
 	currentPageEntries []pager.PageTuple
 	currentTupleIndex  int
+	currentLeftPage    uint16
+	currentRightPage   uint16
 	pager              *pager.Pager
 }
 
@@ -286,6 +290,8 @@ func (c *Cursor) GotoFirstRecord() bool {
 	}
 	c.currentPageEntries = candidatePage.GetEntries()
 	c.currentTupleIndex = 0
+	_, c.currentLeftPage = candidatePage.GetLeftPageNumber()
+	_, c.currentRightPage = candidatePage.GetRightPageNumber()
 	return true
 }
 
@@ -321,5 +327,16 @@ func (c *Cursor) GotoNext() bool {
 		c.currentTupleIndex += 1
 		return true
 	}
+	if c.currentRightPage != 0 {
+		candidatePage := c.pager.GetPage(c.currentRightPage)
+		if len(candidatePage.GetEntries()) == 0 {
+			return false
+		}
+		c.currentPageEntries = candidatePage.GetEntries()
+		c.currentTupleIndex = 0
+		_, c.currentLeftPage = candidatePage.GetLeftPageNumber()
+		_, c.currentRightPage = candidatePage.GetRightPageNumber()
+		return true
+	}
 	return false
 }
diff --git a/pager/pager.go b/pager/pager.go
@@ -244,6 +244,34 @@ func (p *Page) SetParentPageNumber(pageNumber uint16) {
 	copy(p.content[PARENT_POINTER_OFFSET:PARENT_POINTER_OFFSET+PAGE_POINTER_SIZE], bpn)
 }
 
+func (p *Page) GetLeftPageNumber() (hasLeft bool, pageNumber uint16) {
+	pn := binary.LittleEndian.Uint16(p.content[LEFT_POINTER_OFFSET : LEFT_POINTER_OFFSET+PAGE_POINTER_SIZE])
+	if pn == EMPTY_PARENT_PAGE_NUMBER {
+		return false, EMPTY_PARENT_PAGE_NUMBER
+	}
+	return true, pn
+}
+
+func (p *Page) SetLeftPageNumber(pageNumber uint16) {
+	bpn := make([]byte, PAGE_POINTER_SIZE)
+	binary.LittleEndian.PutUint16(bpn, pageNumber)
+	copy(p.content[LEFT_POINTER_OFFSET:LEFT_POINTER_OFFSET+PAGE_POINTER_SIZE], bpn)
+}
+
+func (p *Page) GetRightPageNumber() (hasRight bool, pageNumber uint16) {
+	pn := binary.LittleEndian.Uint16(p.content[RIGHT_POINTER_OFFSET : RIGHT_POINTER_OFFSET+PAGE_POINTER_SIZE])
+	if pn == EMPTY_PARENT_PAGE_NUMBER {
+		return false, EMPTY_PARENT_PAGE_NUMBER
+	}
+	return true, pn
+}
+
+func (p *Page) SetRightPageNumber(pageNumber uint16) {
+	bpn := make([]byte, PAGE_POINTER_SIZE)
+	binary.LittleEndian.PutUint16(bpn, pageNumber)
+	copy(p.content[RIGHT_POINTER_OFFSET:RIGHT_POINTER_OFFSET+PAGE_POINTER_SIZE], bpn)
+}
+
 func (p *Page) GetNumber() uint16 {
 	return p.number
 }

diff --git a/pager/pager_test.go b/pager/pager_test.go
@@ -60,6 +60,30 @@ func TestPageHelpers(t *testing.T) {
 			t.Errorf("got %d want %d", gotPn, wantPn)
 		}
 	})
+
+	t.Run("get set left page number", func(t *testing.T) {
+		var wantPn uint16 = 21
+		p.SetLeftPageNumber(wantPn)
+		gotHas, gotPn := p.GetLeftPageNumber()
+		if gotHas != true {
+			t.Error("want true got false")
+		}
+		if gotPn != wantPn {
+			t.Errorf("got %d want %d", gotPn, wantPn)
+		}
+	})
+
+	t.Run("get set right page number", func(t *testing.T) {
+		var wantPn uint16 = 33
+		p.SetRightPageNumber(wantPn)
+		gotHas, gotPn := p.GetRightPageNumber()
+		if gotHas != true {
+			t.Error("want true got false")
+		}
+		if gotPn != wantPn {
+			t.Errorf("got %d want %d", gotPn, wantPn)
+		}
+	})
 }
 
 func TestPageSet(t *testing.T) {