Your code isn't doing what you think it is doing. You need to ensure
things aren't eliminated by the compiler.
On Mon, Jul 14, 2014 at 5:57 AM, wangzhijiang999
<wangzhijiang...@aliyun.com> wrote:
> Hi everybody, I found a problem confused me when I tested the mmap
> feature in lucene. I tested to read a file size of 800M by mmap method like
> below:
>
> RandomAccessFile raf = new RandomAccessFile(new File(path), "r");
> FileChannel rafc = raf.getChannel();ByteBuffer buff =
> rafc.map(FileChannel.MapMode.READ_ONLY, 0, rafc.size());
> int len=buff.limit(); byte[] b = new byte[len]; for (int i = 0; i < len;
> i++){ b[i] = buff.get(); }
> After the program finished, the linux cache will be consumed about 800M.
>
>
> RandomAccessFile raf = new RandomAccessFile(new File(path), "r");
> FileChannel rafc = raf.getChannel();ByteBuffer buff =
> rafc.map(FileChannel.MapMode.READ_ONLY, 0, rafc.size());
> int len=buff.limit(); for (int i = 0; i < len; i++){ Byte b=
> buff.get(); }
> But in this way, the linux cache will be consumed just 4M.
>
>
> RandomAccessFile raf = new RandomAccessFile(new File(path), "r");
> FileChannel rafc = raf.getChannel();ByteBuffer buff =
> rafc.map(FileChannel.MapMode.READ_ONLY, 0, rafc.size());
> int len=buff.limit(); byte[] b = new byte[len]; for (int i = 0; i < len;
> i++){ b[i] = buff.get();
> b[i]=0; }
> In this way, the linux cache will be also consumed 4M.
>
> The whole content of the file should be read for above three tests, but for
> the last two testings, the linux system only cached 4M .
> Would somebody give me the explaination about this? Thanks in advane.
>
> Zhijiang Wang
>
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