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"""
Dual‑Write Coordination Service – Production‑Grade Implementation
Ensures data consistency across MySQL, Milvus, and MinIO
"""
import time
import uuid
import threading
from typing import Optional, List, Dict, Any
from dataclasses import dataclass, field
from enum import Enum
from concurrent.futures import ThreadPoolExecutor, as_completed
import logging
import traceback
logger = logging.getLogger(__name__)
class WriteOperation(Enum):
"""Write operation types"""
INSERT = "insert"
UPDATE = "update"
DELETE = "delete"
SYNC = "sync"
class ConsistencyLevel(Enum):
"""Consistency levels"""
STRONG = "strong"
EVENTUAL = "eventual"
CAUSAL = "causal"
@dataclass
class WriteResult:
"""Result of a single write operation"""
success: bool
operation: WriteOperation
target: str
data_id: str
error: Optional[str] = None
latency_ms: float = 0
@dataclass
class DualWriteResult:
"""Aggregated result of a dual‑write operation"""
operation_id: str
overall_success: bool
consistency_achieved: bool
results: List[WriteResult] = field(default_factory=list)
compensation_needed: bool = False
total_latency_ms: float = 0
class DualWriteCoordinator:
"""
Dual‑Write Coordinator
Core features:
1. Orchestrate write order across multiple stores
2. Handle partial failure scenarios
3. Trigger compensation mechanisms
4. Guarantee eventual consistency
"""
def __init__(
self,
mysql_client,
milvus_client,
minio_client,
consistency_level: ConsistencyLevel = ConsistencyLevel.EVENTUAL,
max_retries: int = 3,
retry_delay_base: float = 1.0,
enable_compensation_queue: bool = True
):
self.mysql = mysql_client
self.milvus = milvus_client
self.minio = minio_client
self.consistency_level = consistency_level
self.max_retries = max_retries
self.retry_delay_base = retry_delay_base
self.enable_compensation_queue = enable_compensation_queue
self.compensation_queue = []
self._queue_lock = threading.Lock()
self.stats = {
'total_operations': 0,
'successful_operations': 0,
'compensations_triggered': 0,
'avg_latency_ms': 0,
}
def execute_dual_write(
self,
operation: WriteOperation,
mysql_data: Dict = None,
milvus_data: List[Dict] = None,
minio_file_path: str = None,
minio_file_content: bytes = None,
transaction_context: Dict = None
) -> DualWriteResult:
"""
Execute a dual‑write operation
Parameters:
operation: operation type
mysql_data: dictionary of data to write to MySQL
milvus_data: list of data to write to Milvus
minio_file_path: MinIO object path
minio_file_content: file content as bytes
transaction_context: transaction context (for logging)
"""
op_id = str(uuid.uuid4())[:8]
start_time = time.time()
logger.info(f"[{op_id}] Starting dual‑write operation: {operation.value}")
results = []
all_success = True
compensation_needed = False
try:
if operation == WriteOperation.INSERT:
results = self._execute_insert(
op_id, mysql_data, milvus_data,
minio_file_path, minio_file_content
)
elif operation == WriteOperation.UPDATE:
results = self._execute_update(
op_id, mysql_data, milvus_data, minio_file_path, minio_file_content
)
elif operation == WriteOperation.DELETE:
results = self._execute_delete(op_id, mysql_data, milvus_data, minio_file_path)
failed_targets = [r for r in results if not r.success]
all_success = len(failed_targets) == 0
if not all_success:
compensation_needed = True
logger.warning(
f"[{op_id}] Partial write failure: "
f"{[f'{r.target}({r.error})' for r in failed_targets]}"
)
if self.enable_compensation_queue:
self._enqueue_compensation(
op_id, operation, mysql_data, milvus_data,
minio_file_path, minio_file_content, failed_targets
)
except Exception as e:
logger.error(f"[{op_id}] Dual‑write exception: {e}\n{traceback.format_exc()}")
all_success = False
compensation_needed = True
results.append(WriteResult(
success=False,
operation=operation,
target="coordinator",
data_id=op_id,
error=str(e)
))
elapsed_ms = (time.time() - start_time) * 1000
self.stats['total_operations'] += 1
if all_success:
self.stats['successful_operations'] += 1
result = DualWriteResult(
operation_id=op_id,
overall_success=all_success,
consistency_achieved=all_success or self.consistency_level != ConsistencyLevel.STRONG,
results=results,
compensation_needed=compensation_needed,
total_latency_ms=elapsed_ms
)
logger.info(
f"[{op_id}] Dual‑write completed: success={all_success}, "
f"latency={elapsed_ms:.0f}ms, targets={len(results)}"
)
return result
def _execute_insert(
self,
op_id: str,
mysql_data: Dict,
milvus_data: List[Dict],
minio_path: str,
minio_content: bytes
) -> List[WriteResult]:
"""
Execute insert operation (recommended order: MinIO → MySQL → Milvus)
"""
results = []
if minio_path and minio_content:
result = self._safe_write(
op_id, "minio", WriteOperation.INSERT,
lambda: self._upload_to_minio(minio_path, minio_content),
data_id=minio_path
)
results.append(result)
if not result.success:
return results
if mysql_data:
result = self._safe_write(
op_id, "mysql", WriteOperation.INSERT,
lambda: self._insert_to_mysql(mysql_data),
data_id=mysql_data.get('doc_id', '')
)
results.append(result)
if not result.success:
if minio_path:
try:
self.minio.remove_object('rag-knowledge-base', minio_path)
except:
pass
return results
if milvus_data:
result = self._safe_write(
op_id, "milvus", WriteOperation.INSERT,
lambda: self._insert_to_milvus(milvus_data),
data_id=mysql_data.get('doc_id', '') if mysql_data else ''
)
results.append(result)
return results
def _safe_write(
self,
op_id: str,
target: str,
operation: WriteOperation,
write_func,
data_id: str,
retry: int = 0
) -> WriteResult:
"""
Safely execute a write operation (with retries)
"""
start = time.time()
try:
write_func()
latency = (time.time() - start) * 1000
return WriteResult(
success=True,
operation=operation,
target=target,
data_id=data_id,
latency_ms=latency
)
except Exception as e:
latency = (time.time() - start) * 1000
if retry < self.max_retries:
delay = self.retry_delay_base * (2 ** retry)
logger.warning(
f"[{op_id}] {target} write failed (attempt {retry+1}), "
f"retrying in {delay}s: {e}"
)
time.sleep(delay)
return self._safe_write(
op_id, target, operation, write_func,
data_id, retry + 1
)
else:
logger.error(f"[{op_id}] {target} write ultimately failed: {e}")
return WriteResult(
success=False,
operation=operation,
target=target,
data_id=data_id,
error=str(e),
latency_ms=latency
)
def _upload_to_minio(self, path: str, content: bytes):
"""Upload file to MinIO"""
self.minio.put_object(
bucket_name="rag-knowledge-base",
object_name=path,
data=content,
length=len(content)
)
def _insert_to_mysql(self, data: Dict):
"""Insert data into MySQL"""
sql = """
INSERT INTO documents
(doc_id, title, source_type, business_tag, oss_key, status)
VALUES (%s, %s, %s, %s, %s, %s)
"""
self.mysql.execute(sql, (
data['doc_id'],
data['title'],
data['source_type'],
data.get('business_tag', ''),
data.get('oss_key', ''),
'completed'
))
def _insert_to_milvus(self, data_list: List[Dict]):
"""Batch insert data into Milvus"""
if data_list:
self.milvus.insert(
collection_name="rag_vectors",
data=data_list
)
def _enqueue_compensation(
self,
op_id: str,
operation: WriteOperation,
mysql_data: Dict,
milvus_data: List[Dict],
minio_path: str,
minio_content: bytes,
failed_targets: List[WriteResult]
):
"""Add failed operation to the compensation queue"""
with self._queue_lock:
compensation_item = {
'operation_id': op_id,
'operation': operation,
'mysql_data': mysql_data,
'milvus_data': milvus_data,
'minio_path': minio_path,
'minio_content': minio_content,
'failed_targets': [t.target for t in failed_targets],
'created_at': time.time(),
'retry_count': 0
}
self.compensation_queue.append(compensation_item)
self.stats['compensations_triggered'] += 1
logger.info(f"[{op_id}] Added to compensation queue, current queue length: {len(self.compensation_queue)}")
def process_compensation_queue(self, max_items: int = 100):
"""
Process failed operations in the compensation queue
Should be called by a background scheduled task
"""
with self._queue_lock:
items_to_process = self.compensation_queue[:max_items]
self.compensation_queue = self.compensation_queue[max_items:]
processed = 0
success_count = 0
for item in items_to_process:
if item['retry_count'] >= self.max_retries:
logger.error(
f"Compensation operation reached max retries, giving up: {item['operation_id']}"
)
continue
item['retry_count'] += 1
try:
result = self.execute_dual_write(
operation=item['operation'],
mysql_data=item['mysql_data'],
milvus_data=item['milvus_data'],
minio_file_path=item['minio_path'],
minio_file_content=item['minio_content']
)
if result.overall_success:
success_count += 1
logger.info(f"Compensation succeeded: {item['operation_id']}")
else:
with self._queue_lock:
self.compensation_queue.append(item)
except Exception as e:
logger.error(f"Compensation execution exception: {item['operation_id']}, {e}")
with self._queue_lock:
self.compensation_queue.append(item)
processed += 1
logger.info(
f"Compensation queue processing complete: processed={processed}, succeeded={success_count}, "
f"remaining queue length={len(self.compensation_queue)}"
)
return {'processed': processed, 'success': success_count}
def get_statistics(self) -> Dict:
"""Get statistics"""
return {
**self.stats,
'compensation_queue_size': len(self.compensation_queue),
'success_rate': (
self.stats['successful_operations'] / max(1, self.stats['total_operations']) * 100
)
}
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