I think its just a compromise in the design, though it could be
improved. You only ever want a single Writer at a time on the index.
Those two flags are really just hints for when a Writer is first
opened...should it auto-commit and should it overwrite/create...if a
thread tries to writer concurrently with another thread, they will
briefly share a Writer, but generally a new Writer is created fairly often.
The general strategy should be to pick constant values and always pass
them. There is an opening for the issue that you have a Writer and are
adding a doc, and then before releasing that Writer, another Writer from
another thread tries to clear the index with a create=true, and it won't
work. That's not a big concern though.
So the problem really is that these params control what happens when a
new writer is created, but your not guaranteed to be creating a Writer,
it may be cached. You really should pass the same autocommit flag ,
though its not necessary. I am open to suggestions for a more coherent
design, but functionally, it does work. I am also thinking about how to
handle the Analyzer, and I think the solution (the need to init some
indexaccessor params) might involve all these issues.
- Mark
Jay Yu wrote:
Mark,
Looking at your implementation of the DefaultIndexAccessor regarding
the writer, I think there could be a problem: you have only one cached
writer but the getWriter(boolean, boolean) allows 2 booleans, so
ideally, you need 4 cached writer. Otherwise if one starts with a
writer that over writes the existing index, then later he cannot
append docs to the index.
Do I miss sth here or you have not finished the implementation of
getWriter yet?
Thanks!
Jay
Mark Miller wrote:
Ah, thanks for catching that. One of the pieces I did not
finish...the keyword analyzer was placeholder code.
I will take your comments into account and update the code.
I have some other pieces to polish as well. Previously, I extended
and built upon the original code, but I can't give it away, so this
is my attempt at something lessor, but cleaner.
Jay Yu wrote:
Thanks for the tip.
One small improvement on the IndexAccessorFactory might be to allow
user to specify the Analyzer instead of using a default
KeywordAnalyzer, which of course will make your static init of the
cached accessors difficult unless you add more interfaces to the
accessor to allow reset analyzer/Dir as in my own version.
Jay
Mark Miller wrote:
One final note....if you are using the IndexAccessor and you are
only accessing the index from one JVM, you can use the
NoLockFactory and save some sync cost there.
Jay Yu wrote:
Mark,
Great effort getting the original lucene index accessor package in
this shape. I am sure this will benefit a lot of people using
Lucene in a multithread env.
I have a quick question to ask you:
Do you have to use the core Lucene 2.3-dev in order to use the
accessor?
I will take a look at your codes to see if I could help. I used a
slightly modified version of the original package in my project
but it breaks some of my tests. I hope your version works better.
Thanks a lot!
Jay
Mark Miller wrote:
I have sat down and rewrote IndexAccessor from scratch. I copied
in the same reference counting logic, pruned some things, and
tried to make the whole package a bit simpler to use. I have a
few things to do, but its pretty solid already. The only major
thing I'd still like to do is add an option to warm searchers
before putting them in the Searcher cache. Id like to writer some
more tests as well. Any help greatly appreciated if your
interested in using the thing.
http://myhardshadow.com/indexaccessor/trunk/src/test/com/mhs/indexaccessor/SimpleSearchServer.java
Here is a an example of a class that can be instantiated in one
of multiple threads and read /modify a single index without
worrying about what any
of the other threads are doing to the index at any given time.
This is a very simple example of how to use the IndexAccessor and
not necessarily an
example of best practices. The main idea is that you get your
Writer, Searcher, or Reader, and then be sure to release it as
soon as your done with it
in a finally block. For loading, you will want to load many docs
with a Writer (batch them) before releasing it, but remember that
Readers will not get a new view
of the index until you release all of the Writers. So beware
hogging a Writer unless you thats what your intending.
JavaDoc:
http://myhardshadow.com/indexaccessorapi/
Code:
http://myhardshadow.com/indexaccessor/trunk/
Jar:
http://myhardshadow.com/indexaccessorreleases/indexaccessor.jar
Your synchronized block concerns:
The synchronized blocks that control accesss to the IndexAccessor
do not have a huge impact on performance. Keep in mind that all
of the work is not done in a synchonrized block, just the
retrieval of the Searcher, Writer, Reader. Even if the
synchronization makes the method twice as expensive, it is still
overpowered by the cost of parsing queries and searching the
index. This applies with or without contention. I wrote a simple
test and included the output below. You might use the IBM Lock
Analyzer for Java to further analyze these costs. Trust me, this
thing is speedy. Its many times better than using IndexModifier.
Without Contention
Just retrieve and release Searcher 100000 times
----
avg time:6.3E-4 ms
total time:63 ms
Parse query and search on 1 doc 100000 times
----
avg time:0.03107 ms
total time:3107 ms
With Contention (40 other threads running 80000 searches)
Just retrieve and release Searcher 100000 times
----
avg time:0.04643 ms
total time:4643 ms
Parse query and search on 1 doc 100000 times
----
avg time:0.64337 ms
total time:64337 ms
- Mark
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