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From Jørgen Løland <Jorgen.Lol...@Sun.COM>
Subject Re: Lucene integration
Date Wed, 18 Mar 2009 07:46:07 GMT
Geoffrey Hendrey wrote:
> Yeah, that's exactly what I had in mind. The lucene server would receive the binary data,
unpack it, and use the Lucene API to create and modify the Lucene index. 
> Does derby have utilities for unmarshalling the ".dat" format? There must be. Otherwise
there must at least be a clear spec for the binary format.

I'm afraid it's not as easy as unmarshalling the log. The main problem 
is that Derby uses a physical log format; when you do an

"UPDATE employee SET salary=50000 WHERE empid=123"

... the corresponding log record looks something like this:

"Type=update, Table=employee, Page=4321, Index=4, field 3=50000"

Not accurate format, but you get the idea.

Without knowing which record is in index 4 on page 4321, there's no way 
to know which record is updated. Hence, there's nothing to feed into Lucene.

I'm not saying there's no way to hook Lucene and Derby replication 
together, but I doubt that it can be done without having the entire 
database in the receiving end.

> I'd like to clarify that lucene doesn't expect anything as "input". I think this is a
common misconception about lucene. In fact, although lucene does have some sample index builders
for document formats like HTML, the reality is that almost all applications that use lucene
simply parse the data that needs to be indexed and use the lucene IndexWriter to manually
stuff the desired information into the index. There is no need to retain the original data
source. In my current project I build a 12gb lucene index from parsing 1,950,000 source data
> On Mar 16, 2009, at 7:00 AM, Jørgen Løland <Jorgen.Loland@Sun.COM> wrote:
> Geoffrey Hendrey wrote:
> Would it be possible for the derby team to implement lucene support in the following
way? Hook into the asynchronous replication protocol to send committed transactions to a lucene
receiver. I think it is acceptable for the free text search to only "see" committed data.
Alterative to opening the protocol would be to create an abstract ReceiverServer for asynchronous
data, then LuceneReceiver is just a subclass. Thoughts? 
> What does Lucene expect as input? I doubt that the replication code can be easily integrated
with Lucene because...
> 1) The information replication sends from a master to a slave is a physical transaction
log, which is in a derby-internal format. It is not human readable. To get an idea of what
it looks like, you can take a look at logN.dat in one of your databases' log/ directories.
> 2) Replication does not distinguish between committed and uncommitted data; log for all
transactions, committed or not, is sent to the slave.
> This means that before anything is fed into Lucene, the information has to be processed.
This processing is effectively Derby's crash recovery code and is non-trivial to extract.
> Note that I'm not familiar with Lucene.

Jørgen Løland

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