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

问题描述

以下代码导致大约300万行的OutOfMemmoryError: heap space.

The following code is causing a OutOfMemmoryError: heap space for some 3 million rows.

使用64位安装，分配给JVM的内存为4 GB.

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);
}

ArrayList引用的内存在while循环的每次迭代中都可以进行垃圾回收，并且由于堆空间的原因，JVM内部会在抛出OutOfMemoryError之前在内部调用垃圾回收(System.gc()).

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 OutOfMemoryError because of heap space.

那为什么会发生异常?

推荐答案

objOS是ObjectOutputStream吗?

如果是这样，那就是您的问题:ObjectOutputStream强烈引用曾经写入过的每个对象，以避免重复写入同一对象(它只会写一个引用说我之前写过的ID为 x 的那个对象").

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").

这意味着您实际上在泄漏所有 ArrayList个项目.

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

您可以通过调用 reset() 在您的ObjectOutputStream上.由于无论如何在writeObject调用之间似乎都没有使用该缓存，因此可以在writeObject()调用之后直接调用reset().

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

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