java - mongodb分片集群下,count和聚合统计问题
本文介绍了java - mongodb分片集群下,count和聚合统计问题的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
问 题
在mongodb分片集群下,直接用count统计会不准确,用聚合统计则可以
但是在java或mongodb客户端(非命令行)调用mongodb,使用聚合统计时,统计的结果和count同样不准确,请问大神们,我的代码如下,请大神指点,找不到原因!
@Test
public void testCount() throws Exception {
DynamicSqlParameter dsp = new DynamicSqlParameter();
long sT = System.currentTimeMillis();
MongoDatasource mongoDatasource = MongoDatasource.getInstance(mongoService.getDatasource());
DBCollection dbCollection = mongoDatasource.getDB().getCollection("dayFlow");
List arrayList = new ArrayList<>();
DBObject dbObject1 = new BasicDBObject();
dbObject1.put("usedDayFlow", 2);
DBObject dbObject2 = new BasicDBObject();
dbObject2.put("_id", null);
dbObject2.put("count", new BasicDBObject("$sum", 1));
arrayList.add(new BasicDBObject("$match", dbObject1));
arrayList.add(new BasicDBObject("$group", dbObject2));
System.out.println(JSON.serialize(arrayList));
AggregationOutput size = dbCollection.aggregate(arrayList);
System.out.println(size.results());
System.out.println("运行时间:" + ((System.currentTimeMillis() - sT) /1000) + "s");
}
执行结果:
[ { "$match" : { "usedDayFlow" : 2}} , { "$group" : { "_id" : null , "count" : { "$sum" : 1}}}]
[{ "_id" : null , "count" : 1002223}]
该统计结果比实际数据量要多一些,请教大神,对于分片集群的聚合统计要如何操作?
解决方案
该问题已经解决,使用的是最新驱动mongo-java-driver-3.4.0,通过下面的方法可以在分片集群模式下,准确的统计到记录数量,感谢大家的相助!
mongo shell >> db.collection.aggregate([{$match:{categories:"Bakery"},{$group:{"_id":null,"count":{$sum:1}}}}])
public long getCount() {
String user = "用户名";
String database = "admin";
String password = "密码";
MongoCredential credential = MongoCredential.createCredential(user,database, password.toCharArray());
MongoClientOptions options = MongoClientOptions.builder()
.connectionsPerHost(10)
.threadsAllowedToBlockForConnectionMultiplier(10)
.socketTimeout(20000)
.connectTimeout(15000)
.maxWaitTime(50000)
.build();
MongoClient mongoClient = new MongoClient(new ServerAddress("IP地址", "端口"), Arrays.asList(credential), options);
MongoDatabase mongoDatabase = mongoClient.getDatabase("数据库");
MongoCollection<Document> collection = mongoDatabase.getCollection("数据表");
final long[] count = new long[1];
Block<Document> printBlock = new Block<Document>() {
@Override
public void apply(final Document document) {
count[0] = (long) document.get("count");
}
};
Bson bson = Filters.eq("categories", "Bakery");
collection.aggregate(
Arrays.asList(
Aggregates.match(bson),
Aggregates.group(null, Accumulators.sum
("count", 1L))
)
).forEach(printBlock);
return count[0];
}
这篇关于java - mongodb分片集群下,count和聚合统计问题的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文