一次MongoDB分頁查詢致使的OOM問題

OOM描述信息：

2018-09-18 14:46:54.338 [http-nio-8099-exec-8] ERROR o.a.c.c.C.[.[.[.[dispatcherServlet] - Servlet.service() for servlet [dispatcherServlet] in context with path [/party-data-center] threw exception [Handler dispatch failed; nested exception is java.lang.OutOfMemoryError: GC overhead limit exceeded] with root cause
java.lang.OutOfMemoryError: GC overhead limit exceeded
	at org.bson.io.ByteBufferBsonInput.readString(ByteBufferBsonInput.java:154)
	at org.bson.io.ByteBufferBsonInput.readString(ByteBufferBsonInput.java:126)
	at org.bson.BsonBinaryReader.doReadString(BsonBinaryReader.java:245)
	at org.bson.AbstractBsonReader.readString(AbstractBsonReader.java:461)
	at org.bson.codecs.BsonStringCodec.decode(BsonStringCodec.java:31)
	at org.bson.codecs.BsonStringCodec.decode(BsonStringCodec.java:28)
	at org.bson.codecs.BsonArrayCodec.readValue(BsonArrayCodec.java:102)
	at org.bson.codecs.BsonArrayCodec.decode(BsonArrayCodec.java:67)
	at org.bson.codecs.BsonArrayCodec.decode(BsonArrayCodec.java:37)
	at org.bson.codecs.BsonDocumentCodec.readValue(BsonDocumentCodec.java:101)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:84)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:41)
	at org.bson.codecs.configuration.LazyCodec.decode(LazyCodec.java:47)
	at org.bson.codecs.BsonDocumentCodec.readValue(BsonDocumentCodec.java:101)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:84)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:41)
	at org.bson.codecs.configuration.LazyCodec.decode(LazyCodec.java:47)
	at org.bson.codecs.BsonDocumentCodec.readValue(BsonDocumentCodec.java:101)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:84)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:41)
	at org.bson.codecs.configuration.LazyCodec.decode(LazyCodec.java:47)
	at org.bson.codecs.BsonArrayCodec.readValue(BsonArrayCodec.java:102)
	at org.bson.codecs.BsonArrayCodec.decode(BsonArrayCodec.java:67)
	at org.bson.codecs.BsonArrayCodec.decode(BsonArrayCodec.java:37)
	at org.bson.codecs.BsonDocumentCodec.readValue(BsonDocumentCodec.java:101)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:84)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:41)
	at org.bson.codecs.BsonDocumentCodec.readValue(BsonDocumentCodec.java:101)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:84)
	at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:41)
	at com.mongodb.connection.ReplyMessage.<init>(ReplyMessage.java:51)
	at com.mongodb.connection.InternalStreamConnection.receiveCommandMessageResponse(InternalStreamConnection.java:301)

根據以上信息，好像是MongoDB查詢數據的時候佔用內存過大，致使的OOM

導出dump文件而且分析一下 使用MAT打開文件後有個 Problem Suspect 1（最有可能致使內存溢出的提示）

The thread org.apache.tomcat.util.threads.TaskThread @ 0xf9b19fa0 http-nio-8099-exec-8 keeps local variables with total size 58,255,056 (60.49%) bytes.
The memory is accumulated in one instance of "java.lang.Object[]" loaded by "<system class loader>".
The stacktrace of this Thread is available. See stacktrace.


Keywords
java.lang.Object[]

Details »

點擊 See stacktrace

信息量仍是很龐大的，慢慢分析。 找到

at com.mongodb.DB.command(Lcom/mongodb/DBObject;Lcom/mongodb/ReadPreference;Lcom/mongodb/DBEncoder;)Lcom/mongodb/CommandResult; (DB.java:496)
  at com.mongodb.DB.command(Lcom/mongodb/DBObject;Lcom/mongodb/ReadPreference;)Lcom/mongodb/CommandResult; (DB.java:512)
  at com.mongodb.DB.command(Lcom/mongodb/DBObject;)Lcom/mongodb/CommandResult; (DB.java:467)

咱們能夠發現是執行Mongo命令出的錯誤，MongoResult，，，這不是返回的Mongo查詢結果集嗎？？難道是返回的結果集過大？？頗有可能！！！ 繼續往下看。。。

at com.fosung.data.party.dao.DetailDao.detailQuery(Lcom/fosung/data/party/dto/PartyItemDto;)Lcom/fosung/data/party/vo/OutDetailCountVo; (DetailDao.java:314)
  at com.fosung.data.party.dao.DetailDao$$FastClassBySpringCGLIB$$caf49f16.invoke(ILjava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object; (Unknown Source)

此處看到咱們業務代碼的方法，頗有可能就是此處方法致使的OOM，進一步分析咱們的業務方法： 通過咱們仔細分析終於找出問題的緣由： 上面出現問題的緣由是在獲取總條數的時候，沒有加分頁條件（skip和limit）致使查詢全部符合條件的記錄（符合條件的記錄有6w多條），所有加載到內存中，所以致使了OOM問題。

解決： MongoDB使用管道查詢後獲取符合條件的總條數

db.getCollection('user_order').aggregate([
     { "$match" : { "code" : "100002255842358"}} , 
     { "$project" : { "code" : 1 , "yearInfo" : 1 , "personInfo" : 1}} , 
     { "$unwind" : "$yearInfo.counts"} , 
     { "$unwind" : "$yearInfo.counts.code"} , 
     { "$match" : { "yearInfo.counts.code" : { "$in" : [ "1"]}}} , 
     { "$sort" : { "code" : 1 , "yearInfo.counts.sort" : 1}} ,
     { "$lookup" : { "from" : "user_info" , "localField" : "yearInfo.counts.detail" , "foreignField" : "_id" , "as" : "personInfo"}} , 
     { "$unwind" : "$personInfo"} , 
      {"$group":{"_id":null,"totalCount":{"$sum":1}}},
      {"$project":{"totalCount":"$totalCount","_id":0}}
    ])

不須要每次去獲取全部記錄數，再取記錄的條數。

修改完後測試完美經過。。。