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小編給大家分享一下解決mongodb內(nèi)存不足的方法,希望大家閱讀完這篇文章后大所收獲,下面讓我們一起去探討方法吧!
mongodb每一個(gè)文檔默認(rèn)只有16M。聚合的結(jié)果是一個(gè)BSON文檔,當(dāng)超過(guò)16M大小時(shí),就會(huì)報(bào)內(nèi)存不夠錯(cuò)誤。
exceeded memory limit for $group.but didn't allow external sort.
可以采用打開(kāi)使用磁盤(pán)來(lái)解決大小問(wèn)題。例如
db.flowlog.aggregate([{$group:{_id:"$_id"}}], {allowDiskUse: true})
java代碼片段
AggregationOptions options = new AggregationOptions.Builder().allowDiskUse(true).build(); Aggregation agg = Aggregation.newAggregation().withOptions(options);
但是如果結(jié)果集超過(guò)了16M,那么依然會(huì)報(bào)錯(cuò)誤。
采用一個(gè)下面的聚合方法
Aggregation agg = Aggregation.newAggregation( Aggregation.group(field1 , field2 , field3) .sum(field4).as("sampleField1") .sum(field5).as("sampleField2"), Aggregation.project(field4, field5), new AggregationOperation() { @Override public DBObject toDBObject(AggregationOperationContext context) { return new BasicDBObject("$out", "test"); } }).withOptions(options); mongo.aggregate(agg, sourceCollection, Test.class);
如果要在聚合的時(shí)候增加一個(gè)常量,可采用以下形式
Aggregation agg = Aggregation.newAggregation( Aggregation.group( , OnofflineUserHistoryField.MAC , StalogField.UTC_CODE) .sum(OnofflineUserHistoryField.WIFI_UP_DOWN).as(OnofflineUserHistoryField.WIFI_UP_DOWN) .sum(OnofflineUserHistoryField.ACTIVE_TIME).as(OnofflineUserHistoryField.ACTIVE_TIME), Aggregation.project("mac","buildingId","utcCode",OnofflineUserHistoryField.ACTIVE_TIME, OnofflineUserHistoryField.WIFI_UP_DOWN).and( new AggregationExpression() { @Override public DBObject toDbObject(AggregationOperationContext context) { return new BasicDBObject( "$cond", new Object[]{ new BasicDBObject( "$eq", new Object[]{ "$tenantId", 0} ), 20161114, 20161114 }); } }).as("day").andExclude("_id"), 或者 and(new AggregationExpression() { @Override public DBObject toDbObject(AggregationOperationContext context) { return new BasicDBObject("$add", new Object[] { 20141114 }); } }).as("day").andExclude("_id"), new AggregationOperation() { @Override public DBObject toDBObject(AggregationOperationContext context) { return new BasicDBObject("$out", "dayStaInfoTmp"); } }).withOptions(options);
看完了這篇文章,相信你對(duì)解決mongodb內(nèi)存不足的方法有了一定的了解,想了解更多相關(guān)知識(shí),歡迎關(guān)注億速云行業(yè)資訊頻道,感謝各位的閱讀!
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