Java在序列化期间堆空间不足 [英] Java out of heap space during serialization

问题描述

以下代码导致OutOfMemmoryError：约300万行的堆空间。
分配给JVM的内存为4 GB，使用64位安装。

pre $ while（rs.next（））
{

ArrayList< String> arrayList = new ArrayList< String>（）;
for（int i = 1; i< = columnCount; i ++）
{
arrayList.add（rs.getString（i））;
}

objOS.writeObject（arrayList）;



$ b

ArrayList引用的内存有资格在每次迭代中进行垃圾回收while循环和内部JVM调用垃圾回收（ System.gc（）），因为堆空间引发OutOfMemory错误。

那么为什么会发生异常？

解决方案

是 objOS ObjectOutputStream ？

如果是这样，那么这是您的问题： ObjectOutputStream 保持对每一个对象的强烈引用，这是为了避免两次写同一个对象（它只会写一个引用，说我之前编写的那个对象id x ）。

这意味着您正在有效泄漏所有 ArrayList istances。

您可以通过调用 ObjectOutputStream reset（） < C>。由于您似乎并不是使用这个特性，所以您可以直接在 writeObject（）之后调用 reset（） ）呼叫。

The following code is causing a OutOfMemmoryError: heap space for some 3 million rows. Memory allocated to JVM is 4 GB, using 64 bit installation.

while (rs.next())
{

    ArrayList<String> arrayList = new ArrayList<String>();
    for (int i = 1; i <= columnCount; i++)
    {
        arrayList.add(rs.getString(i));
    }

    objOS.writeObject(arrayList);
}

The memory referenced by the ArrayList is eligible for garbage collection in each iteration of the while loop, and internally JVM calls garbage collection (System.gc()) before throwing an OutOfMemory Error because of heap space.

So why is the exception occurring?

解决方案

Is objOS an ObjectOutputStream?

If so, then that's your problem: An ObjectOutputStream keeps a strong reference to every object that was ever written to it in order to avoid writing the same object twice (it will simply write a reference saying "that object that I wrote before with id x").

This means that you're effectively leaking all ArrayList istances.

You can reset that "cache" by calling reset() on your ObjectOutputStream. Since you don't seem to be using that feature anyway, you could call reset() directly after the writeObject() call.

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