Fix MUC room created_at timestamp and add updated_at field

MIGRATION_GUIDE.md

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+# Migration Guide: Add `updated_at` to MUC Rooms
+
+## Overview
+
+This migration adds an `updated_at` column to the `muc_room` table to properly track when rooms are modified, separate from when they were created.
+
+## Why This Change?
+
+Previously, the `created_at` field was incorrectly:
+1. Set to `1970-01-02 00:00:00` for new rooms
+2. Updated every time the room was modified
+3. Confused with `hibernation_time` (when room goes to sleep)
+
+This migration fixes these issues by:
+- Ensuring `created_at` is set correctly on room creation and never changes
+- Adding `updated_at` to track when room configuration is modified
+- Separating concerns between creation time, update time, and hibernation time
+
+## Prerequisites
+
+1. Backup your database before running migration
+2. Stop ejabberd or ensure no rooms are being created/modified during migration
+3. Compile the new ejabberd code
+
+## Migration Steps
+
+### Step 1: Backup Database
+
+```bash
+# MySQL
+mysqldump -u root -p ejabberd > ejabberd_backup_$(date +%Y%m%d).sql
+
+# PostgreSQL
+pg_dump ejabberd > ejabberd_backup_$(date +%Y%m%d).sql
+
+# SQLite
+cp /path/to/ejabberd.db /path/to/ejabberd_backup_$(date +%Y%m%d).db
+```
+
+### Step 2: Run Migration SQL
+
+#### For MySQL/MariaDB:
+
+```sql
+USE ejabberd;
+
+-- Add updated_at column
+ALTER TABLE muc_room ADD COLUMN updated_at timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP;
+
+-- Initialize updated_at with created_at value
+UPDATE muc_room SET updated_at = created_at;
+
+-- Verify
+SELECT name, host, created_at, updated_at FROM muc_room LIMIT 10;
+```
+
+#### For PostgreSQL:
+
+```sql
+\c ejabberd;
+
+-- Add updated_at column
+ALTER TABLE muc_room ADD COLUMN updated_at timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP;
+
+-- Initialize updated_at with created_at value
+UPDATE muc_room SET updated_at = created_at;
+
+-- Verify
+SELECT name, host, created_at, updated_at FROM muc_room LIMIT 10;
+```
+
+#### For SQLite:
+
+```sql
+-- Add updated_at column
+ALTER TABLE muc_room ADD COLUMN updated_at timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP;
+
+-- Initialize updated_at with created_at value
+UPDATE muc_room SET updated_at = created_at;
+
+-- Verify
+SELECT name, host, created_at, updated_at FROM muc_room LIMIT 10;
+```
+
+#### For MSSQL:
+
+```sql
+USE ejabberd;
+
+-- Add updated_at column
+ALTER TABLE muc_room ADD updated_at datetime NOT NULL DEFAULT CURRENT_TIMESTAMP;
+
+-- Initialize updated_at with created_at value
+UPDATE muc_room SET updated_at = created_at;
+
+-- Verify
+SELECT TOP 10 name, host, created_at, updated_at FROM muc_room;
+```
+
+### Step 3: Compile and Restart ejabberd
+
+```bash
+cd /path/to/ejabberd
+./rebar3 compile
+ejabberdctl restart
+```
+
+### Step 4: Verify
+
+```bash
+# Create a test room
+ejabberdctl create_room testroom conference.localhost localhost
+
+# Check database
+# MySQL/PostgreSQL/SQLite:
+SELECT name, created_at, updated_at FROM muc_room WHERE name='testroom';
+
+# Both timestamps should be current time and equal
+
+# Update room option
+ejabberdctl change_room_option testroom conference.localhost title "Test Room"
+
+# Check database again
+SELECT name, created_at, updated_at FROM muc_room WHERE name='testroom';
+
+# created_at should be unchanged, updated_at should be newer
+```
+
+## Rollback
+
+If you need to rollback:
+
+```sql
+-- MySQL/PostgreSQL/SQLite
+ALTER TABLE muc_room DROP COLUMN updated_at;
+
+-- MSSQL
+ALTER TABLE muc_room DROP COLUMN updated_at;
+```
+
+Then restore your backup and use the old ejabberd code.
+
+## Troubleshooting
+
+### Issue: Migration fails with "column already exists"
+
+**Solution:** The column may have been added in a previous attempt. Check if it exists:
+
+```sql
+-- MySQL
+SHOW COLUMNS FROM muc_room LIKE 'updated_at';
+
+-- PostgreSQL
+SELECT column_name FROM information_schema.columns 
+WHERE table_name='muc_room' AND column_name='updated_at';
+
+-- SQLite
+PRAGMA table_info(muc_room);
+```
+
+If it exists, skip to Step 3.
+
+### Issue: Old rooms still have `1970-01-02` in `created_at`
+
+**Solution:** This is expected for rooms created before the migration. You can optionally update them:
+
+```sql
+-- Set created_at to updated_at for old rooms
+UPDATE muc_room 
+SET created_at = updated_at 
+WHERE created_at < '1971-01-01 00:00:00';
+```
+
+### Issue: Performance concerns on large databases
+
+**Solution:** For very large `muc_room` tables (>1M rows), consider:
+
+1. Add the column without default first:
+```sql
+ALTER TABLE muc_room ADD COLUMN updated_at timestamp NULL;
+```
+
+2. Update in batches:
+```sql
+-- MySQL
+UPDATE muc_room SET updated_at = created_at WHERE updated_at IS NULL LIMIT 10000;
+-- Repeat until all rows updated
+
+-- PostgreSQL
+UPDATE muc_room SET updated_at = created_at WHERE updated_at IS NULL;
+```
+
+3. Make it NOT NULL after all rows are updated:
+```sql
+ALTER TABLE muc_room MODIFY updated_at timestamp NOT NULL;
+```
+
+## Benefits After Migration
+
+1. ✅ Accurate room creation timestamps
+2. ✅ Track when room configuration changes
+3. ✅ Better analytics and reporting
+4. ✅ Clearer separation of concerns
+5. ✅ No more `1970-01-02 00:00:00` timestamps!
+
+## Support
+
+If you encounter issues, please report them on the ejabberd GitHub repository with:
+- Database type and version
+- ejabberd version
+- Error messages
+- Output of `SELECT * FROM muc_room LIMIT 1;`