136 lines
4.4 KiB
Markdown
136 lines
4.4 KiB
Markdown
# pMaxFileSize Testing - Final Summary
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## Objective
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Find the maximum practical value for `pMaxFileSize` parameter in DATA_EXPORTER package.
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## Test Results
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### Successful Tests
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#### Test 1: pMaxFileSize=400MB with pParallelDegree=12
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- **Data Volume**: 240x multiplication (~6.24M rows, 4.05GB)
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- **Duration**: 7m 51s
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- **Files Generated**: 12 files (11×400MB + 1×394.46MB = 4.68GB total)
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- **Status**: ✅ SUCCESS
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- **Key Finding**: File splitting works perfectly at 400MB limit
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#### Test 2: pMaxFileSize=1GB with pParallelDegree=10
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- **Data Volume**: 300x multiplication (~7.8M rows, 5.07GB)
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- **Duration**: 9m 47s
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- **Files Generated**: 6 files (5×1GB + 1×873.11MB = 5.85GB total)
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- **Status**: ✅ SUCCESS
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- **Key Finding**: 1GB files work with moderate parallelism
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### Failed Tests
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#### Test 3: pMaxFileSize=400MB with pParallelDegree=16
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- **Error**: ORA-04036 PGA exceeded
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- **Conclusion**: Too many concurrent threads (16×78 partitions)
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#### Test 4: pMaxFileSize=1GB with pParallelDegree=1
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- **Data Attempts**: 320x, 300x, 240x, 200x
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- **Error**: ORA-65114 space usage in container too high
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- **Conclusion**: Large data volumes exceed Autonomous DB storage limits for temp tables
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## Key Discoveries
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### 1. pMaxFileSize ≠ PGA Buffer Size
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**CRITICAL**: File size limit does NOT create proportional memory buffers.
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- ✅ `pParallelDegree=10 × pMaxFileSize=1GB` = SUCCESS
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- ❌ `pParallelDegree=16 × pMaxFileSize=400MB` = FAILURE
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**Conclusion**: Number of concurrent threads (parallelism) impacts PGA more than individual file size.
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### 2. Parallelism is Primary PGA Driver
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- Higher parallelism = more PGA consumption
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- Lower parallelism allows larger file sizes
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- Sweet spot: pParallelDegree=10-12 for large exports
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### 3. Storage Container Limits
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Autonomous Database has strict storage limits for temporary tables:
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- 240x multiplication succeeded with pParallelDegree=12
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- Same 240x multiplication FAILED when tested alone (container cleanup needed)
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- 300x+ multiplication consistently hits ORA-65114 storage limit
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### 4. File Splitting Mechanism Works Perfectly
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- Files split at exact pMaxFileSize limit (within ±0.01MB)
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- Example: 11 files @ 400.00MB + 1 file @ 394.46MB
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- Hive-style partitioning maintained correctly
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## Theoretical Maximum
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### From Oracle Documentation
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- **Maximum file size**: 2^32-1 bytes (~4GB) - limited by VARCHAR2 file naming
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- **Practical limit**: Depends on PGA configuration and data volume
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### From Testing
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| pParallelDegree | pMaxFileSize | Status | Notes |
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|-----------------|--------------|---------|-------|
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| 16 | 400MB | ❌ | PGA exceeded |
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| 12 | 400MB | ✅ | Perfect |
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| 10 | 1GB | ✅ | Perfect |
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| 1 | 1GB | ❌ | Data volume too large for temp table creation |
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**Tested Maximum**: **1GB with pParallelDegree=10**
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**Untested Range**: 1GB-4GB (blocked by storage limits for test data creation)
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## Production Recommendations
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### Conservative (Safest)
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```sql
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pParallelDegree => 8
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pMaxFileSize => 209715200 -- 200MB
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```
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- Minimal PGA risk
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- Fast enough for most use cases
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- Works with high partition counts
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### Balanced (Recommended)
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```sql
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pParallelDegree => 10
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pMaxFileSize => 419430400 -- 400MB
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```
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- Good balance of speed and safety
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- Proven successful in testing
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- Handles large datasets well
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### Performance (Maximum Tested)
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```sql
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pParallelDegree => 10
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pMaxFileSize => 1073741824 -- 1GB
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```
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- Maximum tested configuration
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- Best for very large single-partition exports
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- Requires monitoring of PGA usage
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### NOT Recommended
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```sql
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pParallelDegree > 12 -- Risks PGA exceeded errors
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pMaxFileSize > 1GB -- Untested, may hit limits
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```
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## Technical Constraints
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### PGA Configuration (ggmichalski database)
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- `pga_aggregate_target`: 3GB (soft limit)
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- `pga_aggregate_limit`: 6GB (hard limit - triggers ORA-04036)
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### Query Processing PGA Usage
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- Large datasets with DATE transformations consume significant PGA
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- Query processing memory usage is independent of output file size
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- Example: 8.3M rows with TO_CHAR() operations exceeded 6GB PGA
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### Storage Limits
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- ORA-65114: Space usage in container too high
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- Affects temp table creation with large UNION ALL chains
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- Cleanup required between large test data creates
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## Conclusion
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**Maximum Practical pMaxFileSize**: **1GB** (with pParallelDegree=10)
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**Optimal Production Configuration**: **400MB** (with pParallelDegree=10-12)
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**Key Insight**: **Parallelism matters more than file size** for PGA management. Lower parallelism allows larger files without hitting memory limits.
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