From 054b15bc45b9d12d25e0a7932dc6fbcb60aeed07 Mon Sep 17 00:00:00 2001
From: terence tsao <terence@prysmaticlabs.com>
Date: Sat, 7 Mar 2020 00:06:01 +0100
Subject: [PATCH] Add SlotsPerArchivedPoint flag and a check (#5023)

* Flag

* Service

* Tests

* Tests and comments

* Lint

* Add to usages

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>
---
 beacon-chain/flags/base.go                  |  7 ++++++
 beacon-chain/main.go                        |  1 +
 beacon-chain/state/stategen/BUILD.bazel     |  2 ++
 beacon-chain/state/stategen/service.go      | 11 +++++++++
 beacon-chain/state/stategen/service_test.go | 27 +++++++++++++++++++++
 beacon-chain/usage.go                       |  1 +
 6 files changed, 49 insertions(+)
 create mode 100644 beacon-chain/state/stategen/service_test.go

diff --git a/beacon-chain/flags/base.go b/beacon-chain/flags/base.go
index efd4e4051..d110eb797 100644
--- a/beacon-chain/flags/base.go
+++ b/beacon-chain/flags/base.go
@@ -97,4 +97,11 @@ var (
 		Usage: "A slasher provider string endpoint. Can either be an grpc server endpoint.",
 		Value: "127.0.0.1:5000",
 	}
+	// SlotsPerArchivedPoint specifies the number of slots between the archived points, to save beacon state in the cold
+	// section of DB.
+	SlotsPerArchivedPoint = cli.IntFlag{
+		Name:  "slots-per-archive-point",
+		Usage: "The slot durations of when an archived state gets saved in the DB.",
+		Value: 128,
+	}
 )
diff --git a/beacon-chain/main.go b/beacon-chain/main.go
index bec514f80..b704c0f35 100644
--- a/beacon-chain/main.go
+++ b/beacon-chain/main.go
@@ -46,6 +46,7 @@ var appFlags = []cli.Flag{
 	flags.ArchiveValidatorSetChangesFlag,
 	flags.ArchiveBlocksFlag,
 	flags.ArchiveAttestationsFlag,
+	flags.SlotsPerArchivedPoint,
 	cmd.BootstrapNode,
 	cmd.NoDiscovery,
 	cmd.StaticPeers,
diff --git a/beacon-chain/state/stategen/BUILD.bazel b/beacon-chain/state/stategen/BUILD.bazel
index 6a17e9eab..4d1d87df5 100644
--- a/beacon-chain/state/stategen/BUILD.bazel
+++ b/beacon-chain/state/stategen/BUILD.bazel
@@ -18,6 +18,7 @@ go_library(
         "//beacon-chain/state:go_default_library",
         "//shared/bytesutil:go_default_library",
         "//shared/featureconfig:go_default_library",
+        "//shared/params:go_default_library",
         "@com_github_pkg_errors//:go_default_library",
         "@com_github_prysmaticlabs_ethereumapis//eth/v1alpha1:go_default_library",
         "@com_github_prysmaticlabs_go_ssz//:go_default_library",
@@ -31,6 +32,7 @@ go_test(
     srcs = [
         "epoch_boundary_root_test.go",
         "replay_test.go",
+        "service_test.go",
     ],
     embed = [":go_default_library"],
     deps = [
diff --git a/beacon-chain/state/stategen/service.go b/beacon-chain/state/stategen/service.go
index 65f6d9b42..1e15eba78 100644
--- a/beacon-chain/state/stategen/service.go
+++ b/beacon-chain/state/stategen/service.go
@@ -4,6 +4,7 @@ import (
 	"sync"
 
 	"github.com/prysmaticlabs/prysm/beacon-chain/db"
+	"github.com/prysmaticlabs/prysm/shared/params"
 )
 
 // State represents a management object that handles the internal
@@ -22,3 +23,13 @@ func New(db db.NoHeadAccessDatabase) *State {
 		epochBoundarySlotToRoot: make(map[uint64][32]byte),
 	}
 }
+
+// This verifies the archive point frequency is valid. It checks the interval
+// is a divisor of the number of slots per epoch. This ensures we have at least one
+// archive point within range of our state root history when iterating
+// backwards. It also ensures the archive points align with hot state summaries
+// which makes it quicker to migrate hot to cold.
+func verifySlotsPerArchivePoint(slotsPerArchivePoint uint64) bool {
+	return slotsPerArchivePoint > 0 &&
+		slotsPerArchivePoint%params.BeaconConfig().SlotsPerEpoch == 0
+}
diff --git a/beacon-chain/state/stategen/service_test.go b/beacon-chain/state/stategen/service_test.go
new file mode 100644
index 000000000..ddb958f35
--- /dev/null
+++ b/beacon-chain/state/stategen/service_test.go
@@ -0,0 +1,27 @@
+package stategen
+
+import (
+	"testing"
+
+	"github.com/prysmaticlabs/prysm/shared/params"
+)
+
+func Test_verifySlotsPerArchivePoint(t *testing.T) {
+	type tc struct {
+		input  uint64
+		result bool
+	}
+	tests := []tc{
+		{0, false},
+		{1, false},
+		{params.BeaconConfig().SlotsPerEpoch, true},
+		{params.BeaconConfig().SlotsPerEpoch + 1, false},
+		{params.BeaconConfig().SlotsPerHistoricalRoot, true},
+		{params.BeaconConfig().SlotsPerHistoricalRoot + 1, false},
+	}
+	for _, tt := range tests {
+		if got := verifySlotsPerArchivePoint(tt.input); got != tt.result {
+			t.Errorf("verifySlotsPerArchivePoint(%d) = %v, want %v", tt.input, got, tt.result)
+		}
+	}
+}
diff --git a/beacon-chain/usage.go b/beacon-chain/usage.go
index 9286b1cea..868e9f58b 100644
--- a/beacon-chain/usage.go
+++ b/beacon-chain/usage.go
@@ -91,6 +91,7 @@ var appHelpFlagGroups = []flagGroup{
 			flags.HTTPWeb3ProviderFlag,
 			flags.SetGCPercent,
 			flags.UnsafeSync,
+			flags.SlotsPerArchivedPoint,
 		},
 	},
 	{