mongodb-gridfs下载文件报Sort exceeded memory limit of 104857600 bytes异常

报错详细信息

com.mongodb.MongoQueryException: Query failed with error code 292 and error message 'Executor error during find command :: caused by :: Sort exceeded memory limit of 104857600 bytes, but did not opt in to external sorting.' on server 11.51.141.63:27017
	at com.mongodb.internal.operation.FindOperation.lambda$execute$1(FindOperation.java:670)
	at com.mongodb.internal.operation.OperationHelper.lambda$withSourceAndConnection$2(OperationHelper.java:564)
	at com.mongodb.internal.operation.OperationHelper.withSuppliedResource(OperationHelper.java:589)
	at com.mongodb.internal.operation.OperationHelper.lambda$withSourceAndConnection$3(OperationHelper.java:563)
	at com.mongodb.internal.operation.OperationHelper.withSuppliedResource(OperationHelper.java:589)
	at com.mongodb.internal.operation.OperationHelper.withSourceAndConnection(OperationHelper.java:562)
	at com.mongodb.internal.operation.FindOperation.lambda$execute$2(FindOperation.java:661)
	at com.mongodb.internal.async.function.RetryingSyncSupplier.get(RetryingSyncSupplier.java:65)
	at com.mongodb.internal.operation.FindOperation.execute(FindOperation.java:692)
	at com.mongodb.internal.operation.FindOperation.execute(FindOperation.java:86)
	at com.mongodb.client.internal.MongoClientDelegate$DelegateOperationExecutor.execute(MongoClientDelegate.java:191)
	at com.mongodb.client.internal.MongoIterableImpl.execute(MongoIterableImpl.java:135)
	at com.mongodb.client.internal.MongoIterableImpl.iterator(MongoIterableImpl.java:92)
	at com.mongodb.client.gridfs.GridFSDownloadStreamImpl.getCursor(GridFSDownloadStreamImpl.java:240)
	at com.mongodb.client.gridfs.GridFSDownloadStreamImpl.getChunk(GridFSDownloadStreamImpl.java:215)
	at com.mongodb.client.gridfs.GridFSDownloadStreamImpl.getBuffer(GridFSDownloadStreamImpl.java:277)
	at com.mongodb.client.gridfs.GridFSDownloadStreamImpl.read(GridFSDownloadStreamImpl.java:101)
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解决方式（给fs.chunks集合的files_id字段加索引）如

db.fs.chunks.find();

db.fs.chunks.getIndexes();
# 加索引
db.fs.chunks.createIndex({files_id: 1, n: 1}, {unique: true});
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加上索引后问题得以解决！

---

针对网上说的

1、直接修改系统限制内存大小的变量，如

use admin
db.auth("adminuser","passwd")
db.adminCommand({setParameter:1, internalQueryExecMaxBlockingSortBytes:335544320})
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执行这个命令需要admin用户认证成功，当时没有创建admin用户，也不好停掉MongoDB服务去创建admin用户，所以当时没有使用过此方式。当然不是所有的版本都有此变量，可以通过如下命令查询所有可修改的变量

db.adminCommand({getParameter: '*'})
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如果查到了就可以通过以上命令修改变量值，当然如MongoDB版本是5.0以上的，也可以直接修改配置文件如

setParameter:
  internalQueryExecMaxBlockingSortBytes: 335544320
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2、开启使用磁盘（allowDiskUse）如

db.getCollection('fs.chunks').aggregate([
{$group:{_id:"$title",count:{$sum:1},title:{$addToSet:"$title"},ids:{$addToSet:"$_id"}}},{$match:{count:{$gt:1}}}],
{allowDiskUse:true})
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也可以从代码层面开启使用磁盘，具体可自行搜索一下。

具体的配置含义也没有说清楚，当时试了很多次还是不行。估计是某个配置项没有配好，或者是不适用GridFs下载问题！

3、找到具体报错的集合，然后添加合适的索引。

如上面解决方式，问题得以解决。

希望能帮助到您！