Thanks again, Robert. Could you please explain "preload"? Which
functionality is that? we discussed in this thread before about a preload.
Is there a Lucene url / site that i can look at for preload?
Thanks for the explanations. This thread will be useful for many folks i
believe.
Best regards
On 2/23/21 4:15 PM, Robert Muir wrote:
On Tue, Feb 23, 2021 at 4:07 PM <baris.ka...@oracle.com
<mailto:baris.ka...@oracle.com>> wrote:
What i want to achieve: Problem statement:
base case is disk based Lucene index with FSDirectory
speedup case was supposed to be in memory Lucene index with
MMapDirectory
On 64-bit systems, FSDirectory just invokes MMapDirectory already. So
you don't need to do anything.
Either way MMapDirectory or NIOFSDirectory are doing the same thing:
reading your index as a normal file and letting the operating system
cache it.
The MMapDirectory is just better because it avoids some overheads,
such as read() system call, copying and buffering into java memory
space, etc etc.
Some of these overheads are only getting worse, e.g.
spectre/meltdown-type fixes make syscalls 8x slower on my computer. So
it is good that MMapDirectory avoids it.
So I suggest just stop fighting the operating system, don't give your
J2EE container huge amounts of ram, let the kernel do its job.
If you want to "warm" a cold system because nothing is in kernel's
cache, then look into preload and so on. It is just "reading files" to
get them cached.
