Autonomous Database provides 3 service names:
- HIGH: Dedicated CPU, highest performance, **3x cost of LOW**
- MEDIUM: Shared CPU, balanced
- LOW: Most sharing, cheapest, sufficient for OLTP

# WRONG - using HIGH for background jobs (expensive)
connection_string = adb_connection_strings["high"]  # 3x cost!

# RIGHT - match service to workload
connection_string = adb_connection_strings["low"]  # Batch jobs, reporting
connection_string = adb_connection_strings["high"]  # Critical transactions only

# WRONG assumption - "stopped" database is free
Stop ADB at night to save costs

# Reality:
Stopped ADB charges:
- Storage: $0.025/GB/month continues
- Backups: Retention charges continue
- Compute: ZERO (only part that stops)

Example: 1TB ADB stopped 16 hrs/day
- Compute savings: $584/month × 67% = $391 saved
- Storage cost: $25.60/month (still charged)
- Net savings: $391/month (not $610 expected)

OCI Database password requirements (strict regex):
- 12-30 characters
- 2+ uppercase, 2+ lowercase
- 2+ numbers, 2+ special (#-_)
- NO username in password
- NO repeating chars (aaa, 111)

# WRONG - fails validation
--admin-password "MyPass123"  # Only 1 special char, < 12 chars

# RIGHT - meets requirements
--admin-password "MyP@ssw0rd#2024"  # 2 upper, 2 lower, 2 num, 2 special, 16 chars

| Clone Type | Use Case | Cost | Refresh | When Source Deleted |
|------------|----------|------|---------|---------------------|
| **Full clone** | Prod → Dev (one-time) | Full ADB cost | Cannot refresh | Clone survives |
| **Refreshable clone** | Prod → Test (weekly refresh) | Storage only (~30%) | Manual refresh | Clone deleted |
| **Metadata clone** | Schema-only copy | Minimal | N/A | Clone survives |

# WRONG - full clone for dev environment that needs weekly prod data
oci db autonomous-database create-from-clone-adb \
  --clone-type FULL  # Wastes $500/month, no refresh capability

# RIGHT - refreshable clone for test environments
oci db autonomous-database create-refreshable-clone \
  # Costs $150/month storage, can refresh from prod weekly

# WRONG - deletes Container Database with PDBs inside (data loss)
oci db database delete --database-id <cdb-ocid>
# All pluggable databases deleted with no warning!

# RIGHT - check for PDBs first
oci db pluggable-database list --container-database-id <cdb-ocid>
# If PDBs exist, decide: unplug, clone, or explicitly delete each

# WRONG - application uses ADMIN credentials
app_config = {
    'user': 'ADMIN',
    'password': admin_password  # Full database control!
}

# RIGHT - create app-specific user with least privilege
CREATE USER app_user IDENTIFIED BY <password>;
GRANT CONNECT, RESOURCE TO app_user;
GRANT SELECT, INSERT, UPDATE ON app_schema.* TO app_user;
# ADMIN only for DBA tasks, never in application code

Always-Free Autonomous Database limits:
- 1 OCPU max (cannot scale beyond)
- 20 GB storage max
- 1 database per tenancy per region
- NO private endpoints
- NO auto-scaling

# WRONG - trying to scale always-free database
oci db autonomous-database update \
  --autonomous-database-id <adb-ocid> \
  --cpu-core-count 2  # FAILS: Always-free max is 1 OCPU

# RIGHT - convert to paid tier first, THEN scale
oci db autonomous-database update \
  --autonomous-database-id <adb-ocid> \
  --is-free-tier false  # Convert to paid
# Now can scale to 2+ OCPUs

"Connection refused" or "Wallet error"?
│
├─ Wallet file issues?
│  ├─ Check: TNS_ADMIN env variable set?
│  │  └─ export TNS_ADMIN=/path/to/wallet
│  ├─ Check: sqlnet.ora has correct wallet location?
│  │  └─ WALLET_LOCATION = (SOURCE = (METHOD = file) (METHOD_DATA = (DIRECTORY="/path/to/wallet")))
│  └─ Check: Wallet password correct?
│
├─ Network security?
│  ├─ Private endpoint ADB?
│  │  └─ Check: Source IP in NSG/security list?
│  │  └─ Check: VPN/FastConnect for on-premises access?
│  └─ Public endpoint ADB?
│     └─ Check: Database whitelisted your IP? (Access Control List)
│
├─ Database state?
│  └─ Check: Lifecycle state = AVAILABLE (not STOPPED, UPDATING)?
│     └─ oci db autonomous-database get --autonomous-database-id <ocid> --query 'data."lifecycle-state"'
│
└─ Service name wrong?
   └─ Check: Using correct service name from tnsnames.ora?
      └─ HIGH: <dbname>_high
      └─ MEDIUM: <dbname>_medium
      └─ LOW: <dbname>_low

Usage: 8 hrs/day × 5 days = 40 hrs/week (24% utilization)
Compute cost: $0.36/OCPU-hr × 2 × 40 × 4.3 weeks = $124/month
Storage cost: $0.025/GB/month × 1000 = $25/month
Total: $149/month

Compute cost: $0.36/OCPU-hr × 1 × 730 hrs = $263/month
Storage cost: $25/month
Total: $288/month

# DANGER - unbounded auto-scaling
resource "oci_database_autonomous_database" "prod" {
  cpu_core_count = 2
  is_auto_scaling_enabled = true  # Can scale to 3× (6 OCPUs!)
}

# Cost: 2 OCPUs × $0.36 × 730 = $526/month baseline
# If auto-scales to 6 OCPUs during peak: $1,578/month (3× surprise bill!)

# SAFER - set scaling limit
# (Not available via API, must set in console: Manage Scaling → Max OCPU count)

Scenario: 1 TB ADB, keep 2 years of backups for compliance

Wrong assumption: Automatic backups are free forever
Reality: Automatic backups deleted 60 days after ADB deletion

Right approach: Manual backup before deleting ADB
Cost: $0.025/GB × 1000 GB × 24 months = $600 for 2-year retention

DB System or Exadata
└─ Container Database (CDB)
   └─ Pluggable Database (PDB)  ← Application connects here
      └─ Schemas, tables, etc.

# WRONG - trying to connect to CDB
sqlplus admin/pass@cdb-host:1521/ORCLCDB

# RIGHT - connect to PDB inside CDB
sqlplus app_user/pass@cdb-host:1521/PDB1

# Unplug PDB → creates XML metadata file
oci db pluggable-database unplug --pdb-id <ocid>
# PDB still exists in storage, can re-plug elsewhere
# Charges continue until DELETE