Linux-Server-Management-Toolkit/docs/MYSQL_RESTORE_DATABASE_COMPARISON.md

MySQL Restore Script — Database Comparison Feature

Date: February 27, 2026 Feature: Post-Recovery Verification via Data Comparison Status: ✅ IMPLEMENTED Script: /root/server-toolkit/modules/backup/mysql-restore-to-sql.sh

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Executive Summary

Added a comprehensive database comparison function compare_databases() that verifies the recovered database matches the original live database. This feature provides detailed analysis of schema differences and row count discrepancies without making any changes — purely read-only verification.

What was added: 1 new function + 1 menu integration Lines added: ~200 lines Syntax validation: ✅ PASSED Integration: Menu option [C] in main workflow loop

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Purpose

After successfully recovering a database and creating an SQL dump, users can verify that the recovered data matches the original before importing into production. This prevents silent data loss.

Key question this answers: "Did the recovery process successfully extract all tables and rows, or did we lose data?"

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How It Works

Step 1: User Selects [C] from Menu

════════════════════════════════════════════════════════════════
                    Restore Workflow Menu
════════════════════════════════════════════════════════════════

Completed steps:
  [✓] Step 1: Live MySQL Directory detected
  [✓] Step 3: Database selected (wordpress_db)

Choose action:
  [1] Go to Step 1 (Detect live MySQL data directory)
  [2] Go to Step 2 (Set restore data location)
  [3] Go to Step 3 (Select database)
  [4] Go to Step 4 (Configure restore options)
  [5] Go to Step 5 (Create SQL dump)
  [C] Compare original vs recovered database        ← User selects [C]
  [R] Review current state
  [0] Exit

Select action (0-5, C, R): C

Step 2: Automatic Instance Management

If the second MySQL instance (with recovered data) is not currently running:

• Script automatically starts it
• Runs comparison
• Optionally stops it (user's choice)

If the second MySQL instance is already running (e.g., from Step 5):

• Uses existing instance for comparison
• No restart needed

Step 3: Comparison Analysis

Compares three dimensions:

A. Schema Comparison

• Counts tables in both databases
• Identifies missing tables (in recovered but not original)
• Identifies extra tables (in original but not recovered)

B. Row Count Comparison

• Compares row count for each table
• Shows detailed discrepancies (original vs recovered)
• Calculates percentage difference for each table
• Shows total rows in both databases

C. Overall Assessment

Provides clear verdict:

• ✅ Databases Match: All tables present, all row counts identical
• ⚠️ Minor Discrepancies: 1-2 rows missing (likely temp/session data - safe)
• ❌ Major Discrepancies: Multiple rows or tables missing (needs investigation)

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Example Output: Successful Comparison

════════════════════════════════════════════════════════════════
DATABASE COMPARISON: Original vs Recovered
════════════════════════════════════════════════════════════════
Original database: wordpress_db (live MySQL)
Recovered database: wordpress_db (second instance)

════════════════════════════════════════════════════════════════
SCHEMA COMPARISON
════════════════════════════════════════════════════════════════

Metric                                         Result
────────────────────────────────────────────────────────────────
Original table count                           12
Recovered table count                          12
✓ Table count matches
✓ All tables present in both databases

════════════════════════════════════════════════════════════════
ROW COUNT COMPARISON
════════════════════════════════════════════════════════════════

Table                          Original Rows    Recovered Rows
────────────────────────────────────────────────────────────────────────────────
wp_commentmeta                 124              124 ✓
wp_comments                    8                8 ✓
wp_links                       0                0 ✓
wp_options                     389              389 ✓
wp_postmeta                    2,847            2,847 ✓
wp_posts                       145              145 ✓
wp_term_relationships          198              198 ✓
wp_term_taxonomy               35               35 ✓
wp_termmeta                    0                0 ✓
wp_terms                       32               32 ✓
wp_usermeta                    41               41 ✓
wp_users                       3                3 ✓

Total rows:
  Original:  3,822 rows
  Recovered: 3,822 rows

✓ All table row counts match!

════════════════════════════════════════════════════════════════
SUMMARY
════════════════════════════════════════════════════════════════

✓ DATABASES MATCH - Recovery appears successful!

The recovered database has:
  • All tables present (12 tables)
  • Matching row counts in all tables
  • Total of 3,822 rows recovered

Safe to import recovered dump into production database.

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Example Output: Discrepancies Found

════════════════════════════════════════════════════════════════
DATABASE COMPARISON: Original vs Recovered
════════════════════════════════════════════════════════════════
Original database: wordpress_db (live MySQL)
Recovered database: wordpress_db (second instance)

════════════════════════════════════════════════════════════════
SCHEMA COMPARISON
════════════════════════════════════════════════════════════════

Metric                                         Result
────────────────────────────────────────────────────────────────
Original table count                           12
Recovered table count                          12
✓ Table count matches
✓ All tables present in both databases

════════════════════════════════════════════════════════════════
ROW COUNT COMPARISON
════════════════════════════════════════════════════════════════

Table                          Original Rows    Recovered Rows
────────────────────────────────────────────────────────────────────────────────
wp_commentmeta                 124              124 ✓
wp_comments                    8                8 ✓
wp_links                       0                0 ✓
wp_options                     389              389 ✓
wp_postmeta                    2,847            2,834 ✗
wp_posts                       145              143 ✗
wp_term_relationships          198              198 ✓
wp_term_taxonomy               35               35 ✓
wp_termmeta                    0                0 ✓
wp_terms                       32               32 ✓
wp_usermeta                    41               41 ✓
wp_users                       3                3 ✓

Total rows:
  Original:  3,822 rows
  Recovered: 3,802 rows

✗ Row count mismatches found (2 tables affected)

  ✗ wp_postmeta
    Original: 2,847 rows
    Recovered: 2,834 rows
    Difference: -13 rows (-0%)

  ✗ wp_posts
    Original: 145 rows
    Recovered: 143 rows
    Difference: -2 rows (-1%)

════════════════════════════════════════════════════════════════
SUMMARY
════════════════════════════════════════════════════════════════

⚠ DISCREPANCIES DETECTED

Issues found:
  • Row count differences (2 tables)

Next steps:
  1. Review the discrepancies above
  2. If minor (1-2 rows), likely temporary/session data - safe to import
  3. If major, try a higher recovery mode (higher forces better recovery)
  4. Run comparison again after re-recovery with different mode

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Integration with Recovery Workflow

When to Use

Best time: After Step 5 completes successfully (dump created)

Why here:

• Second MySQL instance is still running with recovered data
• Dump has been created and is ready to verify
• Can immediately try different recovery mode if issues found

Menu Flow

Step 1 → Step 2 → Step 3 → Step 4 → Step 5 (Dump created)
    ↓       ↓       ↓       ↓       ↓
    └───────┴───────┴───────┴───────┴→ [C] Compare
                    ↓
            [Issue found? Retry Step 5 with higher mode]

Scenario: Using Comparison to Guide Recovery Mode Selection

User completes Step 5 with recovery mode 0
  ↓
Dump created successfully
  ↓
User selects [C] for comparison
  ↓
Comparison shows:
  - wp_postmeta: 100 rows missing
  - wp_users: 1 row missing
  ↓
User knows mode 0 is insufficient
  ↓
User goes back to Step 4 → selects mode 5
  ↓
User runs Step 5 again with mode 5
  ↓
User selects [C] again
  ↓
Comparison shows: All rows match ✓

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Function Specification

compare_databases(ORIGINAL_DB, RECOVERED_DB)

Purpose: Compare original live database with recovered database

Parameters:

• ORIGINAL_DB: Database name in live MySQL
• RECOVERED_DB: Database name in second instance (usually same name)

Returns:

• 0: All tables and rows match (safe to import)
• 1: Discrepancies found (review details)

What it does:

1. Verifies both databases exist
2. Gets list of tables from both databases
3. Compares table counts
4. Identifies missing/extra tables
5. Gets row counts for each table
6. Shows detailed discrepancies
7. Provides overall verdict and next steps

Important notes:

• Read-only: Makes no changes to either database
• Safe: Can run multiple times without side effects
• Requires: Second MySQL instance to be running (auto-starts if needed)
• Time: Takes ~5-30 seconds depending on table count

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Instance Management

Auto-Start Second Instance

If second instance is not running when user selects [C]:

Script detects: socket not found
  ↓
Starts second instance automatically
  ↓
Runs comparison
  ↓
Asks: "Keep second instance running? (y/n)"
  ↓
User choice:
  [y] → Instance stays running (user can run Step 5 again)
  [n] → Instance stops (cleanup)

Instance Already Running

If second instance is already running (e.g., from Step 5):

Script detects: socket exists
  ↓
Uses existing instance (no restart)
  ↓
Runs comparison
  ↓
Instance remains running (user hasn't exited menu)

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Data Integrity Scenarios

Scenario 1: Healthy Recovery (All Tables Match)

Original: 12 tables, 3,822 rows
Recovered: 12 tables, 3,822 rows
Status: ✅ SAFE TO IMPORT

Recommendation: Dump is ready for production database import

Scenario 2: Minor Data Loss (1-2 Rows Missing)

Original: 12 tables, 3,822 rows
Recovered: 12 tables, 3,820 rows (2 rows missing)
Status: ⚠ REVIEW NEEDED

Analysis:

• Usually temporary/session data (wp_options, wp_usermeta)
• Likely safe to import (data is ~99.95% complete)
• Recommend: Verify missing rows aren't critical

Recommendation: Safe to import (unless missing rows are critical)

Scenario 3: Major Data Loss (Multiple Tables Missing Rows)

Original: 12 tables, 3,822 rows
Recovered: 12 tables, 3,500 rows (322 rows missing, 8%)
Status: ❌ NEEDS HIGHER RECOVERY MODE

Analysis:

• Recovery mode 0-4 insufficient
• Indicates table corruption at recovery mode level

Recommendation: Try recovery mode 5 or 6, rerun dump, recompare

Scenario 4: Schema Differences (Missing Table)

Original: 12 tables
Recovered: 11 tables (wp_posts missing)
Status: ❌ TABLE NOT RECOVERED

Analysis:

• Table corruption prevents recovery at current mode
• May be unrecoverable or need much higher mode

Recommendation: Review error logs, try mode 6, or restore separately

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Actionable Recommendations

Based on comparison results, script provides specific next steps:

Finding	Severity	Recommendation
All tables match, all rows match	✅ Green	Import dump immediately
1-2 rows missing (temp data)	🟡 Yellow	Safe to import (verify critical tables first)
Multiple tables with row loss	🔴 Red	Try recovery mode 5+, rerun dump, recompare
Missing tables	🔴 Red	Investigate error logs, may need separate mysql/ restore
Extra tables in recovered	🟡 Yellow	Likely from previous recovery attempts, ignore

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Limitations

By Design

• Read-only: Comparison only, no fixing
• Row count only: Doesn't check data quality (just that rows exist)
• Same database name: Assumes recovered database has same name as original
• Live MySQL required: Original database must still be in live MySQL

Possible Future Enhancements

• Check data checksum of rows (not just count)
• Compare individual row contents
• Compare table schemas (CREATE TABLE)
• Generate detailed diff report
• Auto-fix missing rows (not implemented by design)

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Integration with Other Features

With Phase 1 (Validation)

• Phase 1 checks if files exist and system tables accessible
• Comparison validates if recovery succeeded

With Phase 2 (Error Monitoring)

• Phase 2 monitors errors during recovery
• Comparison provides data-level verification

With Phase 3 (Menu Loop)

• Phase 3 provides menu interface
• Comparison is menu option [C]
• User can run comparison → retry Step 5 if needed

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Menu Changes

Before

Choose action:
  [1] Go to Step 1 (Detect live MySQL data directory)
  [2] Go to Step 2 (Set restore data location)
  [3] Go to Step 3 (Select database)
  [4] Go to Step 4 (Configure restore options)
  [5] Go to Step 5 (Create SQL dump)
  [R] Review current state
  [0] Exit

Select action (0-5, R):

After

Choose action:
  [1] Go to Step 1 (Detect live MySQL data directory)
  [2] Go to Step 2 (Set restore data location)
  [3] Go to Step 3 (Select database)
  [4] Go to Step 4 (Configure restore options)
  [5] Go to Step 5 (Create SQL dump)
  [C] Compare original vs recovered database    ← NEW
  [R] Review current state
  [0] Exit

Select action (0-5, C, R):

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Code Changes

Added Function

• compare_databases() (~200 lines)
  • Schema comparison
  • Row count comparison
  • Detailed discrepancy reporting
  • Overall verdict with recommendations

Modified Menu

• Updated menu display to show [C] option
• Added case handler for [C] selection
• Integrated with instance management
• Instance auto-start if needed

Syntax Validation

✅ PASSED (bash -n check)

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Testing

Test Case 1: Compare Matching Databases

1. Complete Steps 1-5 with recovery mode 0
2. Select [C] for comparison
3. Expected: "Databases match - all tables and rows present"

Test Case 2: Compare with Row Loss

1. Corrupt a table in recovered instance (simulate bad recovery)
2. Select [C] for comparison
3. Expected: "Row discrepancies detected - shows missing rows"

Test Case 3: Auto-Start Instance

1. Complete Steps 1-5, then go to Step 1
2. Select [C] (instance was shut down after Step 1)
3. Expected: "Starting temporary instance... Running comparison..."

Test Case 4: Skip Comparison

1. Complete Steps 1-5
2. Select [0] to exit (skip comparison)
3. Expected: Menu should exit normally without error

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Quick Reference

# Comparison is built into menu as [C] option
# No direct command-line invocation needed

# But if called directly (for automation):
./mysql-restore-to-sql.sh

# Then from menu:
# [C] → Compare databases
# Shows detailed schema and row count analysis
# 0 if match, 1 if discrepancies

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User Benefits

1. Prevents Silent Data Loss: Know immediately if recovery was complete
2. Guides Recovery Mode Selection: See exactly which tables lost rows
3. Confidence Before Import: Verify before committing to production
4. Audit Trail: Comparison output shows what was recovered
5. No Data Changes: Read-only analysis, can't break anything

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Recommendations for Use

When to use:

• After every recovery (to verify success)
• When unsure if recovery mode was sufficient
• Before importing dump into production

When to skip:

• If database is tiny (<100 rows) - obvious if match
• If you already know recovery failed (skip to retry step)

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Files Modified

1. /root/server-toolkit/modules/backup/mysql-restore-to-sql.sh

   • Added compare_databases() function (~200 lines)
   • Updated menu display to include [C] option
   • Added menu handler for [C] selection
   • Instance management for comparison

2. /root/server-toolkit/docs/MYSQL_RESTORE_DATABASE_COMPARISON.md (this file)

   • Complete feature documentation

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Status: ✅ FEATURE COMPLETE

All requirements met:

• ✅ Database comparison implemented
• ✅ Schema and row count analysis
• ✅ Detailed discrepancy reporting
• ✅ Read-only (no data changes)
• ✅ Menu integration
• ✅ Instance auto-management
• ✅ Syntax validation passed
• ✅ Backward compatible

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Date: February 27, 2026 Status: ✅ DATABASE COMPARISON FEATURE COMPLETE Integration: Phase 3 Menu Loop Next: Optional Phase 4 features (compression, history logging, notifications)