From 843a5378aa9101c0e2aba61e0c2c11b3f122f08f Mon Sep 17 00:00:00 2001
From: you06 <you1474600@gmail.com>
Date: Sat, 9 Oct 2021 12:30:03 +0800
Subject: [PATCH] add readable flag (#320)

Signed-off-by: you06 <you1474600@gmail.com>
---
 internal/unionstore/memdb.go       | 10 +++++-----
 internal/unionstore/memdb_arena.go |  2 +-
 kv/keyflags.go                     | 17 +++++++++++++++--
 3 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/internal/unionstore/memdb.go b/internal/unionstore/memdb.go
index 7833d966..cd0703e0 100644
--- a/internal/unionstore/memdb.go
+++ b/internal/unionstore/memdb.go
@@ -792,7 +792,7 @@ type memdbNode struct {
 	right memdbArenaAddr
 	vptr  memdbArenaAddr
 	klen  uint16
-	flags uint8
+	flags uint16
 }
 
 func (n *memdbNode) isRed() bool {
@@ -814,7 +814,7 @@ func (n *memdbNode) setBlack() {
 func (n *memdbNode) getKey() []byte {
 	var ret []byte
 	hdr := (*reflect.SliceHeader)(unsafe.Pointer(&ret))
-	hdr.Data = uintptr(unsafe.Pointer(&n.flags)) + 1
+	hdr.Data = uintptr(unsafe.Pointer(&n.flags)) + kv.FlagBytes
 	hdr.Len = int(n.klen)
 	hdr.Cap = int(n.klen)
 	return ret
@@ -822,8 +822,8 @@ func (n *memdbNode) getKey() []byte {
 
 const (
 	// bit 1 => red, bit 0 => black
-	nodeColorBit  uint8 = 0x80
-	nodeFlagsMask       = ^nodeColorBit
+	nodeColorBit  uint16 = 0x8000
+	nodeFlagsMask        = ^nodeColorBit
 )
 
 func (n *memdbNode) getKeyFlags() kv.KeyFlags {
@@ -831,5 +831,5 @@ func (n *memdbNode) getKeyFlags() kv.KeyFlags {
 }
 
 func (n *memdbNode) setKeyFlags(f kv.KeyFlags) {
-	n.flags = (^nodeFlagsMask & n.flags) | uint8(f)
+	n.flags = (^nodeFlagsMask & n.flags) | uint16(f)
 }
diff --git a/internal/unionstore/memdb_arena.go b/internal/unionstore/memdb_arena.go
index 0db8090b..5addc883 100644
--- a/internal/unionstore/memdb_arena.go
+++ b/internal/unionstore/memdb_arena.go
@@ -214,7 +214,7 @@ func (a *nodeAllocator) getNode(addr memdbArenaAddr) *memdbNode {
 }
 
 func (a *nodeAllocator) allocNode(key []byte) (memdbArenaAddr, *memdbNode) {
-	nodeSize := 8*4 + 2 + 1 + len(key)
+	nodeSize := 8*4 + 2 + kv.FlagBytes + len(key)
 	addr, mem := a.alloc(nodeSize, true)
 	n := (*memdbNode)(unsafe.Pointer(&mem[0]))
 	n.vptr = nullAddr
diff --git a/kv/keyflags.go b/kv/keyflags.go
index 64146779..133e5079 100644
--- a/kv/keyflags.go
+++ b/kv/keyflags.go
@@ -34,10 +34,13 @@
 
 package kv
 
-// KeyFlags are metadata associated with key
-type KeyFlags uint8
+// KeyFlags are metadata associated with key.
+// Notice that the highest bit is used by red black tree, do not set flags on it.
+type KeyFlags uint16
 
 const (
+	// FlagBytes is the byte size of type KeyFlags
+	FlagBytes               = 2
 	flagPresumeKNE KeyFlags = 1 << iota
 	flagKeyLocked
 	flagNeedLocked
@@ -45,6 +48,7 @@ const (
 	flagNeedCheckExists
 	flagPrewriteOnly
 	flagIgnoredIn2PC
+	flagReadable
 
 	persistentFlags = flagKeyLocked | flagKeyLockedValExist
 )
@@ -84,6 +88,11 @@ func (f KeyFlags) HasIgnoredIn2PC() bool {
 	return f&flagIgnoredIn2PC != 0
 }
 
+// HasReadable returns whether the in-transaction operations is able to read the key.
+func (f KeyFlags) HasReadable() bool {
+	return f&flagReadable != 0
+}
+
 // AndPersistent returns the value of current flags&persistentFlags
 func (f KeyFlags) AndPersistent() KeyFlags {
 	return f & persistentFlags
@@ -115,6 +124,8 @@ func ApplyFlagsOps(origin KeyFlags, ops ...FlagsOp) KeyFlags {
 			origin |= flagPrewriteOnly
 		case SetIgnoredIn2PC:
 			origin |= flagIgnoredIn2PC
+		case SetReadable:
+			origin |= flagReadable
 		}
 	}
 	return origin
@@ -147,4 +158,6 @@ const (
 	SetPrewriteOnly
 	// SetIgnoredIn2PC marks the key will be ignored in 2pc.
 	SetIgnoredIn2PC
+	// SetReadable marks the key is readable by in-transaction read.
+	SetReadable
 )