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From Shad Storhaug <s...@shadstorhaug.com>
Subject RE: Lucene.net file I/O inefficiency and a question
Date Wed, 01 Feb 2017 04:22:42 GMT
Vincent,

Right now, our priorities are:

1. Stabilize the API
2. Fix the tests that are causing NUnit to crash
3. Get a pre-release on NuGet
4. Fix remaining broken tests
5. Fix other bugs and make optimizations

So, these issues while important, are not the highest of priority right now. That said, now
that I have the my current working branch (https://github.com/apache/lucenenet/tree/api-work)
posted on the main repository, you may submit pull requests there. Please DO NOT use the master
branch or #191 branch to make changes, because it will be difficult to merge them. The api-work
branch is more than 1000 commits ahead of #191.

We do need to proceed carefully on these changes, though, because this I/O code has dependencies
with very temperamental code. Two of the "issues" you brought up previously were to reverse
2 of the bug fixes that I put into place. We need to rely on the tests to verify that we have
the correct behavior, and frankly, that is our best tool to determine if it is working correctly.

I agree that a thread-safe implementation of CreateTempFile is required. But, we also need
it to release the file handle immediately before returning. When trying to open then close
with a using block, some tests are failing (I think because there is a delay after the end
of the using block before the file handle is closed). Also, some of the code does not function
correctly if there is a BOM in the file that is created. Both of these issues were difficult
to track down.

While it might be possible to change the design, keep in mind our safest option is to try
to exactly mimic what is going on in Lucene/Java. Changing the design of this piece, means
that the design of half a dozen dependent pieces needs to be changed to work with the new
behavior. And being that we have new behavior, we are off the map as far as the tests are
concerned. We can write new tests, but how do we know the new behavior is right? It also makes
future porting efforts more difficult for changes to pieces that relied on the original behavior.
I don't object, but we need to tread carefully to go into new waters like this.

If you want to help out, I would suggest start by first helping with the effort of fixing
broken tests (currently we have some tests that are causing NUnit to crash), or if you want
to help with getting the API into shape, let me know and I will set some of the tasks aside
for you. Or, if you prefer, perhaps you could write some tests to check for thread-safety
of CreateTempFile - at least then we have a target to shoot for. But let's at least try to
get stable tests before we start changing parts of the design that could break tests that
don't currently run.

Thanks,
Shad Storhaug (NightOwl888)


-----Original Message-----
From: Prescott Nasser [mailto:geobmx540@hotmail.com] 
Sent: Tuesday, January 31, 2017 3:12 PM
To: dev@lucenenet.apache.org
Subject: RE: Lucene.net file I/O inefficiency and a question

Hey Vincent - 

We love any and all help. 

As for contributions, you can create issues in JIRA (https://issues.apache.org/jira/browse/LUCENENET/?selectedTab=com.atlassian.jira.jira-projects-plugin:issues-panel)
- admittedly we aren't great at keeping this up to date or on track. You can also submit a
pull request and state that the code is your original work and you license it under the Apache
License v2 (http://www.apache.org/licenses/LICENSE-2.0)

Best,
~Prescott

-----Original Message-----
From: Van Den Berghe, Vincent [mailto:Vincent.VanDenBerghe@bvdinfo.com] 
Sent: Monday, January 30, 2017 11:46 PM
To: dev@lucenenet.apache.org
Subject: Lucene.net file I/O inefficiency and a question

Hello everyone,

This message contains two subjects, but since the second one is more of a question, I'll use
the first subject as a "hook", hoping to get an answer  to the next one.
(start of  first subject)
There is an inefficient implementation of file I/O in Lucene.net, most notably in FSDirectory.FSIndexOutput.
The number of write calls can be reduced by a factor of 2.
First we see this, which seems to be a copy paste from the Java code:

            /// <summary>
            /// The maximum chunk size is 8192 bytes, because <seealso cref="RandomAccessFile"/>
mallocs
            /// a native buffer outside of stack if the write buffer size is larger.
            /// </summary>
            internal const int CHUNK_SIZE = 8192;

And then further on:

            protected internal override void FlushBuffer(byte[] b, int offset, int size)
            {
                //Debug.Assert(IsOpen);
                while (size > 0)
                {
                    int toWrite = Math.Min(CHUNK_SIZE, size);
                    File.Write(b, offset, toWrite);
                    offset += toWrite;
                    size -= toWrite;
                }
                //Debug.Assert(size == 0);
            }


This is not needed: in .NET FileStream.Write delegates to the native Win32 file implementation
and allocates nothing, regardless the size of the buffer.
Wouldn't it be better to write:

            protected internal override void FlushBuffer(byte[] b, int offset, int size)
            {
              //Debug.Assert(IsOpen);
              File.Write(b, offset, size);
            }

... and get rid of the CHUNK_SIZE?
The default buffer size (from the BufferedIndexOutput class) is 16384 bytes, so this will
reduce the number of I/O calls by 2.
There is a similar modification that can be done for SimpleFSIndexInput.ReadInternal.
There may be other places where similar code is used, but I couldn't conclusively prove a
similar modification would help.
(end of the first subject)

Here's my question:  This is the third suggestion I'm making, based of real-world usage of
Lucene.net:

-          Proposal to speed up implementation of LowercaseFilter/charUtils.toLower

-          CreateTempFile is not thread-safe (no, it really is not)

-          Lucene.net file I/O inefficiency
I'd like to make contributions to the Lucene.net project, but several personal and external
factors are preventing me to be a contributor (in the Apache sense). I also may not have anything
else or significant to contribute after this: there is no way to know.
How can I make sure that these suggestions are actually considered for ending up in the code?
I've seen contributors doing modifications on behalf of other people. I care about problems
being solved, and do not care about who's name is on them. What's the best way to proceed?
Would it be better to post these things on GitHub somewhere?


Vincent


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