Add 2 more durability policies that allow RDONLY tablets to send semi…

…-sync ACKs (#13698)

Signed-off-by: Manan Gupta <[email protected]>

changelog/18.0/18.0.0/summary.md

@@ -21,6 +21,8 @@
   - **[Docker](#docker)**
     - [Debian: Bookworm added and made default](#debian-bookworm)
     - [Debian: Buster removed](#debian-buster)
+  - **[Durability Policies](#durability-policies)**
+    - [New Durability Policies](#new-durability-policies)
 
 ## <a id="major-changes"/>Major Changes
 
@@ -120,4 +122,10 @@ Bullseye images will still be built and available as long as the OS build is cur
 
 Buster LTS supports will stop in June 2024, and Vitess v18.0 will be supported through October 2024. 
 To prevent supporting a deprecated buster build for several months after June 2024, we are preemptively
-removing Vitess support.
+removing Vitess support.
+
+### <a id="durability-policies"/>Durability Policies
+
+#### <a id="new-durability-policies"/>New Durability Policies
+
+2 new inbuilt durability policies have been added to Vitess in this release namely `semi_sync_with_rdonly_ack` and `cross_cell_with_rdonly_ack`. These policies are exactly like `semi_sync` and `cross_cell` respectively, and differ just in the part where the rdonly tablets can also send semi-sync ACKs. 

go/vt/vtctl/reparentutil/durability.go

@@ -43,10 +43,24 @@ func init() {
 		return &durabilityNone{}
 	})
 	RegisterDurability("semi_sync", func() Durabler {
-		return &durabilitySemiSync{}
+		return &durabilitySemiSync{
+			rdonlySemiSync: false,
+		}
 	})
 	RegisterDurability("cross_cell", func() Durabler {
-		return &durabilityCrossCell{}
+		return &durabilityCrossCell{
+			rdonlySemiSync: false,
+		}
+	})
+	RegisterDurability("semi_sync_with_rdonly_ack", func() Durabler {
+		return &durabilitySemiSync{
+			rdonlySemiSync: true,
+		}
+	})
+	RegisterDurability("cross_cell_with_rdonly_ack", func() Durabler {
+		return &durabilityCrossCell{
+			rdonlySemiSync: true,
+		}
 	})
 	RegisterDurability("test", func() Durabler {
 		return &durabilityTest{}
@@ -141,7 +155,9 @@ func (d *durabilityNone) isReplicaSemiSync(primary, replica *topodatapb.Tablet)
 
 // durabilitySemiSync has 1 semi-sync setup. It only allows Primary and Replica type servers to acknowledge semi sync
 // It returns NeutralPromoteRule for Primary and Replica tablet types, MustNotPromoteRule for everything else
-type durabilitySemiSync struct{}
+type durabilitySemiSync struct {
+	rdonlySemiSync bool
+}
 
 // promotionRule implements the Durabler interface
 func (d *durabilitySemiSync) promotionRule(tablet *topodatapb.Tablet) promotionrule.CandidatePromotionRule {
@@ -162,6 +178,8 @@ func (d *durabilitySemiSync) isReplicaSemiSync(primary, replica *topodatapb.Tabl
 	switch replica.Type {
 	case topodatapb.TabletType_PRIMARY, topodatapb.TabletType_REPLICA:
 		return true
+	case topodatapb.TabletType_RDONLY:
+		return d.rdonlySemiSync
 	}
 	return false
 }
@@ -171,7 +189,9 @@ func (d *durabilitySemiSync) isReplicaSemiSync(primary, replica *topodatapb.Tabl
 // durabilityCrossCell has 1 semi-sync setup. It only allows Primary and Replica type servers from a different cell to acknowledge semi sync.
 // This means that a transaction must be in two cells for it to be acknowledged
 // It returns NeutralPromoteRule for Primary and Replica tablet types, MustNotPromoteRule for everything else
-type durabilityCrossCell struct{}
+type durabilityCrossCell struct {
+	rdonlySemiSync bool
+}
 
 // promotionRule implements the Durabler interface
 func (d *durabilityCrossCell) promotionRule(tablet *topodatapb.Tablet) promotionrule.CandidatePromotionRule {
@@ -192,6 +212,8 @@ func (d *durabilityCrossCell) isReplicaSemiSync(primary, replica *topodatapb.Tab
 	switch replica.Type {
 	case topodatapb.TabletType_PRIMARY, topodatapb.TabletType_REPLICA:
 		return primary.Alias.Cell != replica.Alias.Cell
+	case topodatapb.TabletType_RDONLY:
+		return d.rdonlySemiSync && primary.Alias.Cell != replica.Alias.Cell
 	}
 	return false
 }