feat(entities) Adds speculation tree entity and sql schema

entity/BUILD.bazel

@@ -8,6 +8,7 @@ go_library(
         "build.go",
         "change_provider.go",
         "request.go",
+        "speculation_tree.go",
     ],
     importpath = "github.com/uber/submitqueue/entity",
     visibility = ["//visibility:public"],

entity/speculation_tree.go

@@ -0,0 +1,37 @@
+package entity
+
+// SpeculationPathAction defines the possible actions for a speculation path.
+type SpeculationPathAction string
+
+const (
+	// SpeculationPathActionUnknown is the default zero value for SpeculationPathAction.
+	SpeculationPathActionUnknown SpeculationPathAction = ""
+	// TODO: Add comprehensive list of actions
+)
+
+// SpeculationInfo represents metadata about a single speculation path, including the path through the dependency graph, its current state, and the predicted build score.
+type SpeculationInfo struct {
+	// Path represents the speculation path; which is an ordered list of batches.
+	Path []string
+	// Action is a state that this path is in.
+	Action SpeculationPathAction
+	// Score is score for this speculation path.
+	Score float32
+}
+
+// SpeculationTree represents the set of speculation paths constructed for a batch based on its dependency graph.
+type SpeculationTree struct {
+	// BatchID is the batch for which this speculation tree is constructed.
+	BatchID string
+	// Speculations is a list of speculation paths for this batch based on a graph of its
+	// dependents.
+	//
+	// For e.g - Consider batches - queueA/batch/1, queueA/batch/2, queueA/batch/3
+	// such that - queueA/batch/2 and queueA/batch/3 depend on queueA/batch/1
+	//
+	// Speculations for queueA/batch/1 - [{Path: []string{"queueA/batch/1"}, State: "scheduled", Score: 0.1}]
+	// Speculations for queueA/batch/2 - [{Path: []string{"queueA/batch/2"}, State: "scheduled", Score: 0.9}, {Path: []string{"queueA/batch/1", "queueA/batch/2"}, State: "scheduled", Score: 0.3}]
+	// Speculations for queueA/batch/3 - [{Path: []string{"queueA/batch/3"}, State: "scheduled", Score: 0.9}, {Path: []string{"queueA/batch/1", "queueA/batch/3"}, State: "scheduled", Score: 0.3}]
+	//
+	Speculations []SpeculationInfo
+}

extension/storage/mysql/schema/speculation_tree.sql

@@ -0,0 +1,5 @@
+CREATE TABLE IF NOT EXISTS speculation_tree (
+    batch_id VARCHAR(255) NOT NULL,
+    speculations JSON NOT NULL,
+    PRIMARY KEY (batch_id)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;