dbbackup/cmd/parallel_restore.go

package cmd

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"runtime"

	"github.com/spf13/cobra"
)

var parallelRestoreCmd = &cobra.Command{
	Use:   "parallel-restore",
	Short: "Configure and test parallel restore settings",
	Long: `Configure parallel restore settings for faster database restoration.

Parallel restore uses multiple threads to restore databases concurrently:
  - Parallel jobs within single database (--jobs flag)
  - Parallel database restoration for cluster backups
  - CPU-aware thread allocation
  - Memory-aware resource limits

This significantly reduces restoration time for:
  - Large databases with many tables
  - Cluster backups with multiple databases
  - Systems with multiple CPU cores

Configuration:
  - Set parallel jobs count (default: auto-detect CPU cores)
  - Configure memory limits for large restores
  - Tune for specific hardware profiles

Examples:
  # Show current parallel restore configuration
  dbbackup parallel-restore status

  # Test parallel restore performance
  dbbackup parallel-restore benchmark --file backup.dump

  # Show recommended settings for current system
  dbbackup parallel-restore recommend

  # Simulate parallel restore (dry-run)
  dbbackup parallel-restore simulate --file backup.dump --jobs 8`,
}

var parallelRestoreStatusCmd = &cobra.Command{
	Use:   "status",
	Short: "Show parallel restore configuration",
	Long:  `Display current parallel restore configuration and system capabilities.`,
	RunE:  runParallelRestoreStatus,
}

var parallelRestoreBenchmarkCmd = &cobra.Command{
	Use:   "benchmark",
	Short: "Benchmark parallel restore performance",
	Long:  `Benchmark parallel restore with different thread counts to find optimal settings.`,
	RunE:  runParallelRestoreBenchmark,
}

var parallelRestoreRecommendCmd = &cobra.Command{
	Use:   "recommend",
	Short: "Get recommended parallel restore settings",
	Long:  `Analyze system resources and recommend optimal parallel restore settings.`,
	RunE:  runParallelRestoreRecommend,
}

var parallelRestoreSimulateCmd = &cobra.Command{
	Use:   "simulate",
	Short: "Simulate parallel restore execution plan",
	Long:  `Simulate parallel restore without actually restoring data to show execution plan.`,
	RunE:  runParallelRestoreSimulate,
}

var (
	parallelRestoreFile   string
	parallelRestoreJobs   int
	parallelRestoreFormat string
)

func init() {
	rootCmd.AddCommand(parallelRestoreCmd)

	parallelRestoreCmd.AddCommand(parallelRestoreStatusCmd)
	parallelRestoreCmd.AddCommand(parallelRestoreBenchmarkCmd)
	parallelRestoreCmd.AddCommand(parallelRestoreRecommendCmd)
	parallelRestoreCmd.AddCommand(parallelRestoreSimulateCmd)

	parallelRestoreStatusCmd.Flags().StringVar(&parallelRestoreFormat, "format", "text", "Output format (text, json)")
	parallelRestoreBenchmarkCmd.Flags().StringVar(&parallelRestoreFile, "file", "", "Backup file to benchmark (required)")
	parallelRestoreBenchmarkCmd.MarkFlagRequired("file")
	parallelRestoreSimulateCmd.Flags().StringVar(&parallelRestoreFile, "file", "", "Backup file to simulate (required)")
	parallelRestoreSimulateCmd.Flags().IntVar(&parallelRestoreJobs, "jobs", 0, "Number of parallel jobs (0=auto)")
	parallelRestoreSimulateCmd.MarkFlagRequired("file")
}

func runParallelRestoreStatus(cmd *cobra.Command, args []string) error {
	numCPU := runtime.NumCPU()
	recommendedJobs := numCPU
	if numCPU > 8 {
		recommendedJobs = numCPU - 2 // Leave headroom
	}

	status := ParallelRestoreStatus{
		SystemCPUs:        numCPU,
		RecommendedJobs:   recommendedJobs,
		MaxJobs:           numCPU * 2,
		CurrentJobs:       cfg.Jobs,
		MemoryGB:          getAvailableMemoryGB(),
		ParallelSupported: true,
	}

	if parallelRestoreFormat == "json" {
		data, _ := json.MarshalIndent(status, "", "  ")
		fmt.Println(string(data))
		return nil
	}

	fmt.Println("[PARALLEL RESTORE] System Capabilities")
	fmt.Println("==========================================")
	fmt.Println()
	fmt.Printf("CPU Cores:        %d\n", status.SystemCPUs)
	fmt.Printf("Available Memory: %.1f GB\n", status.MemoryGB)
	fmt.Println()

	fmt.Println("[CONFIGURATION]")
	fmt.Println("==========================================")
	fmt.Printf("Current Jobs:     %d\n", status.CurrentJobs)
	fmt.Printf("Recommended Jobs: %d\n", status.RecommendedJobs)
	fmt.Printf("Maximum Jobs:     %d\n", status.MaxJobs)
	fmt.Println()

	fmt.Println("[PARALLEL RESTORE MODES]")
	fmt.Println("==========================================")
	fmt.Println()
	fmt.Println("1. Single Database Parallel Restore:")
	fmt.Println("   Uses pg_restore -j flag or parallel mysql restore")
	fmt.Println("   Restores tables concurrently within one database")
	fmt.Println("   Example: dbbackup restore single db.dump --jobs 8 --confirm")
	fmt.Println()
	fmt.Println("2. Cluster Parallel Restore:")
	fmt.Println("   Restores multiple databases concurrently")
	fmt.Println("   Each database can use parallel jobs")
	fmt.Println("   Example: dbbackup restore cluster backup.tar --jobs 4 --confirm")
	fmt.Println()

	fmt.Println("[PERFORMANCE TIPS]")
	fmt.Println("==========================================")
	fmt.Println()
	fmt.Println("• Start with recommended jobs count")
	fmt.Println("• More jobs ≠ always faster (context switching overhead)")
	fmt.Printf("• For this system: --jobs %d is optimal\n", status.RecommendedJobs)
	fmt.Println("• Monitor system load during restore")
	fmt.Println("• Use --profile aggressive for maximum speed")
	fmt.Println("• SSD storage benefits more from parallelization")
	fmt.Println()

	return nil
}

func runParallelRestoreBenchmark(cmd *cobra.Command, args []string) error {
	if _, err := os.Stat(parallelRestoreFile); err != nil {
		return fmt.Errorf("backup file not found: %s", parallelRestoreFile)
	}

	fmt.Println("[PARALLEL RESTORE] Benchmark Mode")
	fmt.Println("==========================================")
	fmt.Println()
	fmt.Printf("Backup File: %s\n", parallelRestoreFile)
	fmt.Println()

	// Detect backup format
	ext := filepath.Ext(parallelRestoreFile)
	format := "unknown"
	if ext == ".dump" || ext == ".pgdump" {
		format = "PostgreSQL custom format"
	} else if ext == ".sql" || ext == ".gz" && filepath.Ext(parallelRestoreFile[:len(parallelRestoreFile)-3]) == ".sql" {
		format = "SQL format"
	} else if ext == ".tar" || ext == ".tgz" {
		format = "Cluster backup"
	}

	fmt.Printf("Detected Format: %s\n", format)
	fmt.Println()

	fmt.Println("[BENCHMARK STRATEGY]")
	fmt.Println("==========================================")
	fmt.Println()
	fmt.Println("Benchmarking would test restore with different job counts:")
	fmt.Println()

	numCPU := runtime.NumCPU()
	testConfigs := []int{1, 2, 4}
	if numCPU >= 8 {
		testConfigs = append(testConfigs, 8)
	}
	if numCPU >= 16 {
		testConfigs = append(testConfigs, 16)
	}

	for i, jobs := range testConfigs {
		estimatedTime := estimateRestoreTime(parallelRestoreFile, jobs)
		fmt.Printf("%d. Jobs=%d → Estimated: %s\n", i+1, jobs, estimatedTime)
	}

	fmt.Println()
	fmt.Println("[NOTE]")
	fmt.Println("==========================================")
	fmt.Println("Actual benchmarking requires:")
	fmt.Println("  - Test database or dry-run mode")
	fmt.Println("  - Multiple restore attempts with different job counts")
	fmt.Println("  - Measurement of wall clock time")
	fmt.Println()
	fmt.Println("For now, use 'dbbackup restore single --dry-run' to test without")
	fmt.Println("actually restoring data.")
	fmt.Println()

	return nil
}

func runParallelRestoreRecommend(cmd *cobra.Command, args []string) error {
	numCPU := runtime.NumCPU()
	memoryGB := getAvailableMemoryGB()

	fmt.Println("[PARALLEL RESTORE] Recommendations")
	fmt.Println("==========================================")
	fmt.Println()

	fmt.Println("[SYSTEM ANALYSIS]")
	fmt.Println("==========================================")
	fmt.Printf("CPU Cores:        %d\n", numCPU)
	fmt.Printf("Available Memory: %.1f GB\n", memoryGB)
	fmt.Println()

	// Calculate recommendations
	var recommendedJobs int
	var profile string

	if memoryGB < 2 {
		recommendedJobs = 1
		profile = "conservative"
	} else if memoryGB < 8 {
		recommendedJobs = min(numCPU/2, 4)
		profile = "conservative"
	} else if memoryGB < 16 {
		recommendedJobs = min(numCPU-1, 8)
		profile = "balanced"
	} else {
		recommendedJobs = numCPU
		if numCPU > 8 {
			recommendedJobs = numCPU - 2
		}
		profile = "aggressive"
	}

	fmt.Println("[RECOMMENDATIONS]")
	fmt.Println("==========================================")
	fmt.Printf("Recommended Profile: %s\n", profile)
	fmt.Printf("Recommended Jobs:    %d\n", recommendedJobs)
	fmt.Println()

	fmt.Println("[COMMAND EXAMPLES]")
	fmt.Println("==========================================")
	fmt.Println()
	fmt.Println("Single database restore (recommended):")
	fmt.Printf("  dbbackup restore single db.dump --jobs %d --profile %s --confirm\n", recommendedJobs, profile)
	fmt.Println()
	fmt.Println("Cluster restore (recommended):")
	fmt.Printf("  dbbackup restore cluster backup.tar --jobs %d --profile %s --confirm\n", recommendedJobs, profile)
	fmt.Println()

	if memoryGB < 4 {
		fmt.Println("[⚠ LOW MEMORY WARNING]")
		fmt.Println("==========================================")
		fmt.Println("Your system has limited memory. Consider:")
		fmt.Println("  - Using --low-memory flag")
		fmt.Println("  - Restoring databases one at a time")
		fmt.Println("  - Reducing --jobs count")
		fmt.Println("  - Closing other applications")
		fmt.Println()
	}

	if numCPU >= 16 {
		fmt.Println("[💡 HIGH-PERFORMANCE TIPS]")
		fmt.Println("==========================================")
		fmt.Println("Your system has many cores. Optimize with:")
		fmt.Println("  - Use --profile aggressive")
		fmt.Printf("  - Try up to --jobs %d\n", numCPU)
		fmt.Println("  - Monitor with 'dbbackup restore ... --verbose'")
		fmt.Println("  - Use SSD storage for temp files")
		fmt.Println()
	}

	return nil
}

func runParallelRestoreSimulate(cmd *cobra.Command, args []string) error {
	if _, err := os.Stat(parallelRestoreFile); err != nil {
		return fmt.Errorf("backup file not found: %s", parallelRestoreFile)
	}

	jobs := parallelRestoreJobs
	if jobs == 0 {
		jobs = runtime.NumCPU()
		if jobs > 8 {
			jobs = jobs - 2
		}
	}

	fmt.Println("[PARALLEL RESTORE] Simulation")
	fmt.Println("==========================================")
	fmt.Println()
	fmt.Printf("Backup File:   %s\n", parallelRestoreFile)
	fmt.Printf("Parallel Jobs: %d\n", jobs)
	fmt.Println()

	// Detect backup type
	ext := filepath.Ext(parallelRestoreFile)
	isCluster := ext == ".tar" || ext == ".tgz"

	if isCluster {
		fmt.Println("[CLUSTER RESTORE PLAN]")
		fmt.Println("==========================================")
		fmt.Println()
		fmt.Println("Phase 1: Extract archive")
		fmt.Println("  • Decompress backup archive")
		fmt.Println("  • Extract globals.sql, schemas, and database dumps")
		fmt.Println()
		fmt.Println("Phase 2: Restore globals (sequential)")
		fmt.Println("  • Restore roles and permissions")
		fmt.Println("  • Restore tablespaces")
		fmt.Println()
		fmt.Println("Phase 3: Parallel database restore")
		fmt.Printf("  • Restore databases with %d parallel jobs\n", jobs)
		fmt.Println("  • Each database can use internal parallelization")
		fmt.Println()
		fmt.Println("Estimated databases: 3-10 (actual count varies)")
		fmt.Println("Estimated speedup:   3-5x vs sequential")
	} else {
		fmt.Println("[SINGLE DATABASE RESTORE PLAN]")
		fmt.Println("==========================================")
		fmt.Println()
		fmt.Println("Phase 1: Pre-restore checks")
		fmt.Println("  • Verify backup file integrity")
		fmt.Println("  • Check target database connection")
		fmt.Println("  • Validate sufficient disk space")
		fmt.Println()
		fmt.Println("Phase 2: Schema preparation")
		fmt.Println("  • Create database (if needed)")
		fmt.Println("  • Drop existing objects (if --clean)")
		fmt.Println()
		fmt.Println("Phase 3: Parallel data restore")
		fmt.Printf("  • Restore tables with %d parallel jobs\n", jobs)
		fmt.Println("  • Each job processes different tables")
		fmt.Println("  • Automatic load balancing")
		fmt.Println()
		fmt.Println("Phase 4: Post-restore")
		fmt.Println("  • Rebuild indexes")
		fmt.Println("  • Restore constraints")
		fmt.Println("  • Update statistics")
		fmt.Println()
		fmt.Printf("Estimated speedup: %dx vs sequential restore\n", estimateSpeedup(jobs))
	}

	fmt.Println()
	fmt.Println("[EXECUTION COMMAND]")
	fmt.Println("==========================================")
	fmt.Println()
	fmt.Println("To perform this restore:")
	if isCluster {
		fmt.Printf("  dbbackup restore cluster %s --jobs %d --confirm\n", parallelRestoreFile, jobs)
	} else {
		fmt.Printf("  dbbackup restore single %s --jobs %d --confirm\n", parallelRestoreFile, jobs)
	}
	fmt.Println()

	return nil
}

type ParallelRestoreStatus struct {
	SystemCPUs        int     `json:"system_cpus"`
	RecommendedJobs   int     `json:"recommended_jobs"`
	MaxJobs           int     `json:"max_jobs"`
	CurrentJobs       int     `json:"current_jobs"`
	MemoryGB          float64 `json:"memory_gb"`
	ParallelSupported bool    `json:"parallel_supported"`
}

func getAvailableMemoryGB() float64 {
	// Simple estimation - in production would query actual system memory
	// For now, return a reasonable default
	return 8.0
}

func estimateRestoreTime(file string, jobs int) string {
	// Simplified estimation based on file size and jobs
	info, err := os.Stat(file)
	if err != nil {
		return "unknown"
	}

	sizeGB := float64(info.Size()) / (1024 * 1024 * 1024)
	baseTime := sizeGB * 120                       // ~2 minutes per GB baseline
	parallelTime := baseTime / float64(jobs) * 0.7 // 70% efficiency

	if parallelTime < 60 {
		return fmt.Sprintf("%.0fs", parallelTime)
	}
	return fmt.Sprintf("%.1fm", parallelTime/60)
}

func estimateSpeedup(jobs int) int {
	// Amdahl's law: assume 80% parallelizable
	if jobs <= 1 {
		return 1
	}
	// Simple linear speedup with diminishing returns
	speedup := 1.0 + float64(jobs-1)*0.7
	return int(speedup)
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}