在 PyMongo 中使用 compact 命令进行 MongoDB 碎片回收的完整操作指南如下：

一、核心执行方法

from pymongo import MongoClient
import time# 1. 连接到 MongoDB 实例
client = MongoClient("mongodb://username:password@host:27017/dbname?authSource=admin")# 2. 选择目标数据库和集合
db = client["your_database"]
collection = db["your_collection"]# 3. 执行 compact 命令
try:# 执行碎片回收（返回操作ID）result = db.command("compact", collection.name)print(f"Compact operation started. Operation ID: {result['operationTime']}")# 监控操作进度（可选）operation_id = result["operationTime"]while True:current_ops = db.command("currentOp", {"operationTime": operation_id})if not current_ops.get("inprog", []):breakprint("Compact in progress...")time.sleep(10)print("✅ Compact completed successfully!")except Exception as e:print(f"❌ Compact failed: {str(e)}")
finally:client.close()

二、关键参数配置

# 添加额外参数（副本集secondary节点需要force）
result = db.command("compact", collection.name,force=True,              # 强制在secondary节点运行compression={"type": "zlib"},  # 指定压缩算法paddingFactor=1.1,        # 预留空间因子（0-4.0）maxPaddingBytes=1024,     # 最大填充字节tieredStorage={"useRecycledSpace": True}  # Atlas专用
)

三、集群环境操作方案

1. 副本集自动滚动执行

rs_members = ["rs1/mongo1:27017","rs1/mongo2:27017","rs1/mongo3:27017"
]for member in rs_members:member_client = MongoClient(f"mongodb://user:pass@{member}/admin?replicaSet=rs1")# 检查节点类型is_primary = member_client.admin.command("isMaster").get("ismaster")# 降级主节点（每次处理前）if is_primary:member_client.admin.command("replSetStepDown", 300)  # 降级300秒try:db = member_client["your_db"]db.command("compact", "your_collection", force=True)print(f"✅ Compact completed on {member}")except Exception as e:print(f"❌ Failed on {member}: {str(e)}")finally:member_client.close()

2. 分片集群自动处理

# 通过Config Server获取分片列表
config_client = MongoClient("mongodb://config_server:27019")
shards = config_client.config.shards.find()for shard in shards:shard_name = shard["_id"]shard_host = shard["host"].split("/")[-1]  # 提取主机地址try:shard_client = MongoClient(f"mongodb://{shard_host}/admin")# 确认是分片主节点if shard_client.admin.command("isMaster").get("ismaster"):db = shard_client["your_db"]db.command("compact", "your_collection")print(f"✅ Compact on shard {shard_name} completed")else:print(f"⚠️ {shard_host} is not primary, skipped")except Exception as e:print(f"❌ Shard {shard_name} failed: {str(e)}")finally:shard_client.close()

四、操作结果验证

# 对比前后存储状态
pre_stats = collection.stats()
# ... compact 执行 ...
post_stats = collection.stats()print(f"存储优化报告:")
print(f"- 原始大小: {pre_stats['storageSize'] / 1024**2:.2f} MB")
print(f"- 优化后: {post_stats['storageSize'] / 1024**2:.2f} MB")
print(f"- 节省空间: {(pre_stats['storageSize'] - post_stats['storageSize']) / 1024**2:.2f} MB")
print(f"- 碎片率: {100 * (pre_stats['size'] / pre_stats['storageSize'] - 1):.1f}% → "f"{100 * (post_stats['size'] / post_stats['storageSize'] - 1):.1f}%")

五、安全操作注意事项

阻塞机制处理

# 检查当前操作是否被阻塞
if db.current_op({"command.compact": {"$exists": True}}):print("⚠️ Another compact already running")exit()# 设置超时自动中断
client = MongoClient(connectTimeoutMS=30000, socketTimeoutMS=3600000)

磁盘空间保障

# 检查磁盘空间
disk_stats = client.admin.command("fsInfo")
free_space = disk_stats["fsUsedSize"] - disk_stats["fsTotalSize"]
coll_size = collection.stats()["storageSize"]if free_space < coll_size * 1.5:print(f"❌ Insufficient disk space. Need {coll_size*1.5} bytes, only {free_space} available")exit()

Atlas 云服务专用

# Atlas需要特殊授权
client = MongoClient(connect_string, authMechanism="MONGODB-AWS")# 使用分层存储API
compact_opts = {"tieredStorage": {"useRecycledSpace": True,"reclaimSpace": True}
}

六、替代方案实现

无损在线重建方案：

def online_recompact(db_name, coll_name):temp_name = f"{coll_name}_compact_{int(time.time())}"# 1. 创建临时集合db.command("create", temp_name)# 2. 逐步复制数据（避免大事务阻塞）source = db[coll_name]dest = db[temp_name]batch_size = 1000total_docs = source.count_documents({})for skip in range(0, total_docs, batch_size):docs = source.find().skip(skip).limit(batch_size)dest.insert_many(list(docs))# 3. 原集合原子替换source.rename(f"old_{coll_name}", dropTarget=True)dest.rename(coll_name)db[f"old_{coll_name}"].drop()

最佳实践总结

执行窗口选择

# 获取当前时间并判断
from datetime import datetime
current_hour = datetime.now().hour
if 0 <= current_hour < 5:  # 凌晨执行run_compact()
else:print("⚠️ Operation declined: Not in maintenance window")

定时清理脚本框架

import schedule
import timedef weekly_compact():shard_cluster_compact()  # 调用前述集群函数# 每周日凌晨1点执行
schedule.every().sunday.at("01:00").do(weekly_compact)while True:schedule.run_pending()time.sleep(60)

健康检查指标

HEALTH_THRESHOLD = 0.8  # 碎片率阈值def needs_compact(collection):stats = collection.stats()fragmentation = 1 - (stats["size"] / stats["storageSize"])return fragmentation > HEALTH_THRESHOLD# 自动检测执行
if needs_compact(collection):run_compact(collection)