我正在使用 mongo-java-driver 3.0.2。
我有一个使用 MongoCollection.aggregate(List<Bson> pipeline)
的方法排序和限制:
private static MongoIterable<Document> selectTop(int n) {
BasicDBObject sortFields = new BasicDBObject("score", -1);
BasicDBObject sort = new BasicDBObject("$sort", sortFields);
BasicDBObject limit = new BasicDBObject("$limit", n);
List<BasicDBObject> pipeline = new ArrayList<>();
pipeline.add(sort);
pipeline.add(limit);
return playersCollection.aggregate(pipeline);
}
当 n
很大,它失败了:
com.mongodb.MongoCommandException: Command failed with error 16820: 'exception: Sort exceeded memory limit of 104857600 bytes, but did not opt in to external sorting. Aborting operation. Pass allowDiskUse:true to opt in.'
我发现 MongoDB shell 提供了一个方法 db.collection.aggregate(pipeline, options)
( link ) 其中 options
可以包含 allowDiskUse
字段。
我在 Java API 中找不到与此等效的内容。虽然有一个 AggregationOptions类,MongoCollection
类不提供 aggregate(List<Bson> pipeline, AggregationOptions options)
方法。
最佳答案
这仍然适用于 3.0.3 驱动程序:
MongoClient client = new MongoClient(new ServerAddress("127.0.0.1", 27017));
DB test = client.getDB("test");
DBCollection sample = test.getCollection("sample");
List<DBObject> aggregationQuery = Arrays.<DBObject>asList(
new BasicDBObject("$sort",new BasicDBObject("score",-1)),
new BasicDBObject("$limit",1)
);
System.out.println(aggregationQuery);
Cursor aggregateOutput = sample.aggregate(
aggregationQuery,
AggregationOptions.builder()
.allowDiskUse(true)
.build()
);
while ( aggregateOutput.hasNext() ) {
DBObject doc = aggregateOutput.next();
System.out.println(doc);
}
当然你也可以使用更新的类:
MongoClient client = new MongoClient(new ServerAddress("192.168.2.4", 27017));
MongoDatabase db = client.getDatabase("test");
MongoCollection<Document> collection = db.getCollection("sample");
AggregateIterable<Document> result = collection.aggregate(Arrays.asList(
new BasicDBObject("$sort", new BasicDBObject("score", -1)),
new BasicDBObject("$limit", 1)
)).allowDiskUse(true);
MongoCursor<Document> cursor = result.iterator();
while (cursor.hasNext()) {
Document doc = cursor.next();
System.out.println(doc);
}
所以 .aggregate()
在 MongoCollection 上返回 AggregateIterable
类实例,它有一个 .allowDiskuse()
方法以及其他设置聚合选项的方法。
关于java - MongoDB Java 驱动程序 3.x : How to pass allowDiskUse=true to aggregate() method?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31283479/